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Abstract

The installation of dense granular columns by various construction techniques can be used to mitigate liquefaction through a combination of densification, increase of lateral stresses, reinforcement, and drainage. The contributing mechanism of shear reinforcement is isolated and explored using nonlinear three-dimensional (3D) finite-element (FE) analysis. FE models representing both dry and saturated conditions were developed to evaluate cases with and without generation and dissipation of excess pore-water pressures. The shear stress and strain distributions between the granular columns and surrounding soil, and the level of shear stress reduction, were investigated for a practical range of treatment geometries, relative stiffness ratios, vertical stresses, and relative densities of the surrounding soil. A set of 10 acceleration time histories were used as input motions. The FE results show that granular columns undergo a shear strain deformation pattern that is noncompatible with the surrounding soil. As such, the achieved reduction in cyclic stress ratios imposed on the treated soil is far less than that predicted by the conventional shear strain compatibility design approach. Reductions in cyclic stress ratios are insensitive to the applied surface pressure, granular column length/diameter ratio (L/D), and relative density of the surrounding soil for the range of area replacement ratio and column-soil shear modulus ratio examined. A modified design equation to estimate the reduction in cyclic stress ratio provided by dense granular columns is shown to provide good agreement with the FE simulation results.

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... Among the available methods, the implementation of stone columns stands out as a cost-effective, straightforward, and convenient approach for ground improvement. Further, stone columns combine the beneficial effects of densification, reinforcement, and increased drainage, effectively mitigating lateral spreading effects and enhancing the seismic performance of structures during earthquakes (Seed and Booker 1977;Mitchell et al. 1995;Boulanger et al. 1998;Ashford et al. 2000;Adalier et al. 2003;Adalier and Elgamal 2004;Elgamal et al. 2009;Rayamajhi et al. 2016;Badanagki et al. 2018;Lu et al. 2019;Tang et al. 2022). For instance, Jackura and Abghari (1994) discussed the seismic remediation of two California bridge sites, where one site implemented stone columns with actual diameters of 0.9 m, placed at 2.4 m center-to-center spacing to enhance ...
... To potentially mitigate the extent of liquefaction-induced lateral deformation, this study investigates remediation through stone columns (Mitchell et al. 1995;Adalier et al. 2003;Adalier and Elgamal 2004;Elgamal et al. 2009;Rayamajhi et al. 2016;Badanagki et al. 2018;Lu et al. 2019;Tang et al. 2022) for the 3D bridgefoundation-ground system (Figs. 1 and 5). With the same bridge structures and soil materials, five different remediation scenarios (i.e., Scenarios 1-5) employing stone columns are explored (Fig. 5), and Scenario 6 serves as the benchmark unremediated scenario. ...
... In addition to the increased stiffness, stone columns provide drainage paths that play an important role in reducing the extent of excess pore-pressure buildup (Mitchell et al. 1995;Adalier and Elgamal 2004;Elgamal et al. 2009;Rayamajhi et al. 2016;Badanagki et al. 2018;Lu et al. 2019). For illustration, Fig. 9 displays theexcess pore pressure ratio r u contours at the end of shaking [i.e., 15 s in Fig. 6(c)], demonstrating the effects of the earthquake on pore pressure immediately after the shaking stops (before any significant dissipation occurs). ...
Article
Sustainability has emerged as a paramount concern in the construction and development of built infrastructure. This study delves into the environmental impact and vulnerability of an idealized bridge–foundation–ground system using stone columns as a liquefaction countermeasure, focusing on the seismic response in the transverse direction. For that purpose, a nonlinear three-dimensional (3D) finite element framework is established, exploring the influence of stone columns on the vulnerability of the bridge–foundation system. To enhance the reliability of the analysis outcomes, an optimal intensity measure is identified through comprehensive evaluations of efficiency, correlation, coefficient of variation, and sufficiency. Further, systematic assessments of total cost and carbon emissions associated with ground improvement are performed using three different life-cycle assessment (LCA) approaches, including process-based LCA (P-LCA), economic input–output LCA (EIO-LCA), and a hybrid approach that combines P-LCA and EIO-LCA. The results demonstrate that stone columns noticeably reduce liquefaction-induced damage to pile foundations, proving their effectiveness in improving seismic resilience. While several factors influence overall ground improvement design (such as material availability and demobilization), the overall analysis techniques and derived insights systematically quantify sustainability, thereby offering an additional dimension in decision-making when implementing such liquefaction mitigation techniques in seismic-prone regions.
... There are several commonly used approaches to mitigate the liquefaction hazard, such as pile-pinning, granular columns, cementation, and deep soil mixing approaches [3,5,14,22,29,31]. Among these approaches, the installation of dense granular columns has been regarded as an effective tool to improve the dynamic resistance of liquefiable soils, because of the effects of densification, shear reinforcement, and improved drainage capacity [1,6,27]. Specifically, installing granular columns makes a closer arrangement of adjacent soil particles, yielding the densification of soil layers. ...
... In existing studies [5,14,[27][28][29], uniform soil layers are generally considered in modeling the soil-granular column system. For example, Elgamal et al. [14] investigated the effect of granular columns on the lateral deformation of soil-granular column systems, in which homogeneous soil properties were incorporated. ...
... In this study, the PDMY02 model parameters for sands and granular columns reported by Rayamajhi et al. [28] are employed, which are summarized in Table 2. Specifically, the three sets of loose-sand parameters are used to model the stress-strain behavior of the intermediate liquefiable layer with various relative densities, while the dense-sand category is used to describe the stress-strain behavior of both the bottom and top dense-sand layers. These model parameters were calibrated by the produced cyclic resistance ratios with the standard penetration test-based liquefaction correlations under a confining pressure of 100 kPa [27,28]. Specifically, direct simple shear element responses were estimated based on the model parameters and the results were validated with published empirical correlations [15]. ...
Article
Full-text available
In this paper, three-dimensional nonlinear dynamic finite-element analyses are conducted to examine the effect of soil property variability on the lateral displacement (D) of liquefiable ground reinforced by granular columns. A suite of 20 ground motions is selected from the NGA-West2 database as input. A soil-granular column ground system consisting of an intermediate liquefiable layer is modeled in OpenSees. Both the random variable (RV) and random filed (RF) methods are adopted to model the variability of soil property parameters. Dynamic analyses are then conducted to estimate the earthquake-induced deformation of the soil-granular column system. It is found that modeling the variability of soil parameters based on the RV method generally increases the geometric mean and standard deviation (σlnD) of D for the soil-granular column system. Enlarging the spatial correlation of soil parameters in the RF model brings in a slight increase of the mean D and comparable σlnD values, respectively. Hence, incorporating the spatially correlated soil property parameters may not be necessarily increase the variation of D for the soil-granular column system. Specifically, the statistical distribution of D is more sensitive to the vertical scale of fluctuation rather than the horizontal one. The results presented could aid in addressing the variability issue for performance-based design of granular column-reinforced liquefiable ground in engineering applications.
... The dynamic numerical analysis is a fundamental means to study the earthquake response of granular columns composite foundation in liquefiable soils, among which the FE analysis based on Biot's dynamic consolidation equation can fully couple the pore pressure with the dynamic response of the soil skeleton and becomes one of the most extensively used approaches [14]. In order to assess the effectiveness and mitigation of stone columns, three-dimensional FE simulations were implemented on OpenSees in various studies [15][16][17][18][19] with the same computational formulation. These studies assumed the saturated soils to be solid-fluid material following the u-p formulation which is developed based on Biot's theory by Chan [20] and Zienkiewicz et al. [21]. ...
... The constitutive model of soils plays a critical role in this fully coupled numerical approach and decides its prediction capability. The multi-yield surface elastoplastic constitutive PDMY can well describe the cyclic mobility and irreversible shear strain accumulation behavior of liquefiable sand under seismic excitation, which has been verified in many research applications [15][16][17][18][19]26,27]. In addition, with a total of 17 input parameters, the PDMY model allows for a comprehensive multi-factor analysis. ...
... The measured data at the in situ site are also utilized to obtain the parameters. The parameters of the material of the stone columns are determined using the calibration method adopted by Rayamajhi et al. [17] as well as by the design scheme proposed in the last section, as listed in Table 3. Noted that the elastic shear modulus of the stone columns is determined by the design schemes proposed in the last section; the elastic bulk modulus can be calculated as follows [35], where G r is the elastic shear modulus, and ϑ is the Poisson's ratio which is taken as 0.33. ...
Article
Full-text available
To optimize the design of stone columns composite foundation for liquefiable ground improvement in the Tibar Bay Port Project, a 3D Finite Element (FE) analysis is implemented on the earthquake response and liquefaction mitigation effect. Nine improvement schemes are designed with the orthogonal design method. Taking peak ground acceleration and peak excess pore pressure ratio as the target indicators, the influences of four factors, including diameter, replacement ratio, stiffness, permeability ratio, of stone columns are analyzed by means of range analysis, and subsequently, the optimal ground improvement design is obtained. The analysis results indicate that the responses of ground acceleration and excess pore pressure ratio are relatively sensitive to stone columns’ permeability ratio and a little sensitive to the replacement ratio. The stiffness and diameter ranging in the prescribed boundary only have negligible effect. The mitigation effect of drainage is rather significant when the ratio of the stone columns’ permeability to the soils’ permeability is greater than 100.
... The results indicated that the seismic performance of the granular columns is effective in reducing lateral displacements and increasing excess pore pressure dissipation rate. Rayamajhi et al. (2016) and Lu et al. (2019) parametrically investigated to examine the influence of granular columns on liquefaction-induced deformations. 3D numerical analyses showed that granular columns effectively decrease lateral soil displacements depending on the permeabilities of the granular column and the surrounding soil. ...
... Most of the above numerical research has provided useful information in understanding the behavior of HMCs in liquefiable soils. On the other hand, while these studies highlight the effectiveness of HMCs on liquefaction mitigation, some other researches (Demir 2019;Demir andOzener 2019, 2020;Green et al. 2008;Rayamajhi et al. 2016Rayamajhi et al. , 2014 discussed the effectiveness of HMCs in terms of shear reinforcement mechanism which is commonly applied in engineering practice by using conventional design chart proposed by Baez (1995). These numerical studies showed that role of columnar reinforcement in reducing the seismic shear stress in liquefiable soil is less than as it is assumed in engineering practice. ...
... In 2014, a new seismic shear stress reduction factor ( R rd ) and a new shear strain relationship that depends on G r were suggested by Rayamajhi et al. (2014) as a result of 3D linear-elastic parametric analyses as given in Fig. 2. The relationship proposed by Rayamajhi et al. (2014) has not been confirmed with detailed laboratory studies or full-scale field tests. Rayamajhi et al. (2016) carried out nonlinear parametric analyses in order to evaluate the contribution of the shear reinforcement provided by granular columns with and without the generation of excess pore pressures. Nonlinear simulations showed that K G and r estimated from Rayamajhi et al. (2014) can be used for limited G r values. ...
Article
Full-text available
Nowadays, investigating the effectiveness of high modulus columns in liquefaction mitigation is one of the important tasks in earthquake geotechnical engineering. Although there is limited data from the field and laboratory to verify the performance of high modulus columns (HMCs), available case histories, physical model tests, and reliable numerical methods provide important information in order to analyze the role of HMCs in liquefaction mitigation. In this paper, the seismic performance of a liquefied site improved with rammed aggregate piers (RAPs) is investigated through the results of a full-scale field test. Results of cone penetration test (CPT) and cross-hole shear wave velocity (Vs) test before and after RAP treatment at the test site are assessed to achieve properties of the natural (unimproved) soil, RAP, and the surrounding (improved) soil. The effectiveness of RAPs in liquefaction mitigation is evaluated in terms of pre-and post-improvement factor of safeties against liquefaction, liquefaction-induced deformations, and ground failure indices, which are calculated using shear strain compatibility and incompatibility approaches. The research results showed that RAPs exhibit a satisfying performance when computations are made considering shear strain compatibility in the computation of seismic shear stress reduction factor. On the contrary, the effectiveness of RAPs during the shear strain incompatibility approach is significantly smaller than the ones computed from the current design method based on shear strain compatibility approach. The findings of this study provide a basis for the performance-based ground improvement design through HMCs to mitigate soil liquefaction and also extend knowledge about HMC-improved seismic soil response by presenting the results of liquefaction vulnerability parameters before and after soil improvement of a field test study.
... Over the past few decades, dense granular columns (DGCs) have become a common soil improvement strategy for critical geostructures founded on potentially liquefiable deposits (Adalier and Elgamal 2004). Case histories from previous earthquakes using DGCs as a liquefaction countermeasure (Hausler 2002;Nikolaou et al. 2016), as well as previous experimental and numerical studies (e.g., Adalier et al. 2003;Elgamal et al. 2009;Asgari et al. 2013;Rayamajhi et al. 2014Rayamajhi et al. , 2016aBadanagki et al. 2018Badanagki et al. , 2019Tiznado et al. 2020), have generally shown DGCs to be effective in mitigating the consequences of soil liquefaction. However, the influence of various mitigation mechanisms provided by DGCs and their seismic interactions with site and ground motion characteristics are not yet well understood in the context of liquefaction triggering and softening in the treated ground. ...
... Current design procedures, which are based on a conventional liquefaction-triggering analysis (e.g., Boulanger and Idriss 2014) with DGC-modified cyclic stress ratios (CSRs) per Rayamajhi et al. (2016a) do not explicitly account for (1) the activity of each mitigation mechanism provided by DGCs (e.g., ground densification, enhanced drainage, shear reinforcement) and their possible interactions; (2) the influence of DGCs on the dynamic response of the improved soil profile and intensity measure (IM) estimation (i.e., PGA at the soil surface); (3) soil-DGC and layer-to-layer cross-interactions; (4) the most efficient and sufficient IMs that would reduce uncertainty and dependence on other source parameters; and (5) various degrees of soil softening. The primary purpose of this paper is, first, to identify the trends and key predictors of liquefaction in layered soil deposits treated with DGCs and, second, to set the stage for a DGC design methodology that explicitly accounts for the activity of each mechanism of mitigation, soil nonlinearity, soil-DGC and layer-to-layer interactions, the optimum IM (s), and the extent of softening in critical layers. ...
... This simple approach was judged acceptable for these two layers because of their small thickness. Properties for DGCs were selected based on (1) recommendations of Rayamajhi et al. (2016a), who calibrated model properties of DGCs to match empirical design correlations, and (2) strength and permeability tests performed at CU on the same soil type representing DGCs in the centrifuge Li et al. 2018). Fig. 1 shows representative results from the calibration of PDMY02 soil model parameters for Ottawa sand (the critical layer) at different relative densities based on isotropically consolidated, strain-controlled, cyclic, undrained triaxial tests, a free-field centrifuge test, and empirical field observations. ...
Article
This paper presents a probabilistic model for evaluating the liquefaction-triggering hazard in level, layered, and saturated granular soil profiles improved with dense granular columns (DGCs). The model is developed using the results of a comprehensive numerical parametric study, validated with a dynamic centrifuge test, and subsequently tested with the available case histories involving DGCs as a liquefaction countermeasure. The numerical database includes a total of 30,000, three-dimensional (3D), fully coupled, nonlinear, dynamic finite-element simulations with a statistically determined range of layer-, profile-, DGC-, and ground motion-specific input parameters. The criteria for the predicted degree of liquefaction (i.e., full, marginal, and no liquefaction) are based on the peak values of excess pore pressure ratio and shear strain anticipated within each soil layer. A machine learning approach that performs multinomial logistic regression along with variable selection and regularization is used to develop a set of functional forms for estimating the probabilities of full-, marginal-, and no-liquefaction in sites improved with DGCs. The proposed probabilistic model is the first of its kind that explicitly considers variations in the area replacement ratio (A r), stiffness, and drainage capacity of the DGC; the thickness, depth, relative density, and hydraulic conductivity range of each layer; the evolutionary characteristics of ground motions; and the underlying uncertainty in the prediction of pore pressures and shear strains within each layer.
... Phase transformation angle is used to define Table 1. Stone column is assumed to be fully bonded with sand for simplicity [4,6,19,20,24,25]. The sand strata, stone column material and pervious concrete are discretized into 8 noded brick element with u-p formulation. ...
... The thickness of finite element mesh used is 0.5 m. Similar mesh is adopted by Tang et al. [19,20] and Rayamajhi et al. [6,24,25]. Smaller mesh thickness is selected to ensure correct prediction of liquefaction behaviour [22]. ...
... This is due to the presence of rigid PCC column. The similar increase in surface peak acceleration of rigid inclusion is well stated [4,24,25]. Figure 9 shows excess pore pressure generation of PCC case (at depths of 2 m, 4 m, 6 m and 8 m) in comparison with stone column case and free-field case. It is found that the excess pore pressure generated during earthquake shaking is very limited for pervious concrete column improved ground. ...
Article
In this study, liquefaction mitigation potential of improved ground using pervious concrete column is being investigated. The seismic performance of pervious concrete column improved ground is compared with conventional stone column improved ground. Three-dimensional finite element analysis using OpenSeesPL software is conducted to study the ground lateral deformation and excess pore water pressure generation of pervious concrete column improved ground on a mildly sloping soil strata of infinite extent under seismic loading. The soil strata considered is fully saturated sand with an inclination of 4°. The parameters influencing seismic performance of improved ground like area ratio, founding depth of columns, diameter of columns and hydraulic conductivity of columns are considered. It is found from various response parameters that the pervious concrete column improved ground has better seismic performance than conventional stone column improved ground. The lateral deformation profile of pervious concrete column is found to be similar to that of concrete pile, allowing excess pore water pressure to dissipate through the pores of pervious concrete column. It is also concluded that pervious concrete columns could be used as an alternative to conventional stone columns to mitigate liquefaction to a larger extent.
... Stone columns are widely used all over the world for reducing liquefaction. The performance of stone column is well documented during seismic events using full scale field tests, centrifuge tests and numerical modelling [1][2][3][4][5][6][7][8][9]. Recently, the behaviour of encased stone columns subjected to earthquake loading is reported [10,11]. ...
... The materials are modelled with PressureDependMultiYield02 (PDMY02) soil model available in OpenSeesPL software. Half of unit-cell model is analysed because of symmetry [4,5,7,8,10,18]. A 4° inclined sloping strata fully saturated up to ground level is modelled with stone column and pervious concrete column as shown in Fig.1. ...
... Default values available for cohensionless sand of 75% relative density with gravel permeability is used for modelling stone column and pervious concrete column respectively. The column-surrounding soil interface is assumed to be fully bonded for simplicity [4,[6][7][8]10,18]. As the pervious concrete properties are reported similar to concrete, values corresponding to normal concrete properties are selected as model input parameters for pervious concrete. ...
Article
Full-text available
This paper investigates the performance of pervious concrete column improved ground subjected to seismic loading. The seismic performance of pervious concrete column improved ground is also compared with conventional stone column improved ground in responses of lateral displacement, excess pore pressure, ground surface acceleration, shear stress-strain behaviour and stress path. A fully saturated mildly sloping sand strata is considered as unimproved ground. OpenSeesPL software is used to analyse soil models representing unimproved ground and improved ground with stone column and pervious concrete column inclusions. It is found that the pervious concrete column improved ground has better seismic performance than stone column improved ground. The lateral displacement of ground is found to be significantly reduced while using pervious concrete column. Also the use of pervious concrete column has reduced excess pore pressure generation than stone column indicating that the improved ground with pervious concrete column inclusion is efficient in mitigating liquefaction than conventional stone column improved ground.
... However, these effects are not well established yet, and more research is needed for a better understanding in this regard. Rayamajhi et al. (2016) investigated the contribution mechanism of shear reinforcement, increment in lateral stress, and drainage effects with the help of three-dimensional finite-element analyses. They reported that the granular columns undergo a shear strain deformation pattern, which is noncompatible with the surrounding soil contrasting with the conventional design assumption of shear strain compatibility. ...
... The liquefaction in the ground resulted in the mobilisation of shear strength during the shaking, Khosravifar et al. (2018). **The parameters for the granular column are selected per Elgamal, Lu, and Forcellini 2009;Rayamajhi et al. 2016, andKhosravifar et al. (2018). which lead to the excessive deformation of the ground. ...
... The granular column and associated ground (Toyoura Sand) is assigned a uniform permeability value of 0.0066 and 0.0002 m/s, respectively. The assigned uniform properties for the granular column is corresponding to (N1) 60cs of 30 (D R ∼ 80%), per Rayamajhi et al. (2016) and Khosravifar et al. (2018). The random field of (N1) 60cs values with calibrated parameters of the PDMY02 Model are implemented into the OpenSees numerical model with the help of Matlab code. Figure 14 shows the typical variation of the mean and standard deviation of the average settlement and horizontal displacement of the top surface (Z = 0 plane, see Figure 2) of the ground with the granular column. ...
Article
Full-text available
Granular columns have been widely used to mitigate the liquefaction-induced ground deformation. Granular columns steer the quick dissipation of excess pore water pressure generated during the dynamic event. Besides, densification during installation, increment in lateral stress, and apparent shear reinforcement believed to increase the liquefaction resistance of the ground treated with granular columns. However, several case histories and recent research development exhibited the limitations of the effectiveness of granular columns under strong earthquakes. In addition, the mechanism of shear reinforcement because of granular columns is poorly understood. Moreover, the ground is prone to spatial nonuniformity and should to be taken into account for a reliable engineering assessment of the performance of granular columns. A series of three-dimensional nonlinear stochastic analyses are carried out using the OpenSees framework with PDMY02 elasto-plastic soil constitutive model to map the reliability of the overall performance of equally-spaced granular columns. Soil variability is implemented with stochastic realizations of overburden and energy-corrected, equivalent clean sand, (N1)60cs values using spatially correlated Gaussian random field. The reliability of the performance of granular column is assessed based on the stochastic distributions of average surface settlement and horizontal ground displacement and associated degree of confidence. The implications of cumulative absolute velocity, Arias Intensity and peak acceleration of different ground motions on the efficacy of the granular column to mitigate the ground deformation are also discussed.
... Different ground improvement mechanisms such as densification, drainage, reinforcement, or a combination of these mechanisms are commonly used in engineering practice to prevent or minimize the liquefaction-induced soil deformations and its associated damages. These mechanisms are applied in liquefiable soils in order to reduce the risk of liquefaction and its related hazards with different improvement techniques called high modulus columns (HMCs) such as stone columns, rammed aggregate piers, jet grout columns [1][2][3][4][5][6][7][8][9][10][11][12][13]. ...
... In recent years, the performance of HMCs in liquefiable soils has been investigated through available case histories, physical model tests and well-calibrated numerical models [1,2,5,8,9,[14][15][16][17]. In particular, these researches questioned the performance of HMCs in liquefaction mitigation in terms of shear stress distribution or site response effects [2,8,15,[17][18][19]. ...
... In recent years, the performance of HMCs in liquefiable soils has been investigated through available case histories, physical model tests and well-calibrated numerical models [1,2,5,8,9,[14][15][16][17]. In particular, these researches questioned the performance of HMCs in liquefaction mitigation in terms of shear stress distribution or site response effects [2,8,15,[17][18][19]. Although various researches have been carried out on the effectiveness of HMCs in liquefaction mitigation, many questions still remain regarding the use of HMCs as a reinforcing element for liquefaction remediation. ...
Article
In this paper, an extensive parametric study is carried out in order to examine the effectiveness of high modulus columns (HMCs) in liquefaction mitigation using a nonlinear three-dimensional (3D) finite-element (FE) software. For this purpose, a hypothetical liquefiable soil profile of 20 m thick is modeled and parametric analyses are performed by considering different area replacement ratios, shear modulus ratios, improvement depth (slenderness) ratios and input motion intensities. The results of the parametric analyses are evaluated by examining shear stress reduction, shear strain distribution, peak surface acceleration, maximum horizontal acceleration, factor of safety against soil liquefaction, excess pore water pressure ratio, surface settlements, lateral displacements and response spectra. Comparative analyses between unimproved liquefiable soil and improved soil are performed to show the influence of high modulus columns on the response of liquefiable soil. The seismic performance of liquefiable soil reinforced with HMCs is specifically investigated by focusing on the shear strain and shear stress distribution between liquefiable soil and high modulus columns. Therefore, the analysis results are discussed in terms of assumption of shear strain compatibility by comparing the modified equations for shear stress reduction factors suggested in the literature with the one developed in this paper. Additionally, the reliability of the current design methodology for evaluating shear reinforcement of HMCs is discussed by showing effects of shear strain compatibility and incompatibility on the values of factor of safety against liquefaction and recommendations are made related to the use of HMCs in engineering practice.
... Prior numerical parametric studies representing DGCs as unit cells have demonstrated their effectiveness in reducing lateral displacements owing to a combination of drainage and shear reinforcement (e.g., Elgamal et al. 2009;Asgari et al. 2013;Rayamajhi et al. 2016b). They have also provided valuable insight into shear deformations between the columns and their surrounding soil (e.g., Rayamajhi et al. 2016a), and have shown that DGCs can significantly improve site performance, particularly for A r values ranging from about 20% to 30% (again greater than the range reported in successful case histories). Nevertheless, the final settlements predicted by these studies may not be reliable, particularly in thicker liquefiable profiles, because of the limitations in the available soil constitutive models and, in general, the use of a continuum framework to capture sedimentation type volumetric strains (Rayamajhi et al. 2016b;Ramirez et al. 2018). ...
... Recently, based on results from both 3D linear elastic and nonlinear finite-element analyses of DGCs as unit cells, Rayamajhi et al. (2014Rayamajhi et al. ( , 2016a proposed the following modified expression for R rd , limited to cases where r u ≤ 0.8 in the native soil: ...
... This implies that the assumption of a purely shear beam behavior is no longer valid. It also implies that the columns attract significantly less load than predicted by the strain-compatibility assumption (Rayamajhi et al. 2014(Rayamajhi et al. , 2016a. ...
Article
Dense granular columns (DGCs) are generally known to mitigate the liquefaction hazard through a combination of (1) installation-induced ground densification, (2) enhanced drainage, and (3) shear reinforcement. However, the relative contribution of these mitigation mechanisms remains poorly understood. A recent case history of successful embankment performance on a liquefiable site treated with DGCs that had relatively low area replacement ratios (A r) (where drainage is not notably enhanced) suggested that shear reinforcement and installation-induced ground densification may be the two dominant mitigation mechanisms provided by DGCs. In this paper, we present a series of four dynamic centrifuge experiments designed and conducted to test this hypothesis under controlled conditions. Consistent with case history observations and supporting our initial working hypothesis, densification combined with shear reinforcement was shown to be primarily responsible for limiting the embankment's seismic deformations. Additional drainage led to minor improvements in terms of embankment settlement, while increasing its permanent lateral displacement. The results suggest that the combined effects of A r and ratio of maximum shear modulus of the DGCs to that of the surrounding soil (G r) can play a key role in the distribution of stress between DGCs and soil prior to shaking and the extent of softening and strain accumulation in various layers during shaking. For example, it was observed that densification of the liquefiable sand layer around DGCs shifted the generation of larger excess pore pressures to greater depths compared to the DGC-treated test without densification. This led to a base isolation effect that reduced accelerations, degree of softening, and accumulation of shear and volumetric strains at shallower depths, producing a notably improved performance for the soil-embankment system even when the DGC's drainage capacity was inhibited. These observations were attributed to the reinforcement effect of DGCs, the simultaneous reduction in G r due to densification, and a more even transfer of the embankment load onto the soil-column matrix, increasing the stiffness and strength and reducing shear strains in the shallower and looser layer. The presented experimental results point to the importance of accounting for pre-and postinstallation soil density and stiffness in relation to DGCs, confining pressure distributions, kinematic constraints, and activity of various mitigation mechanisms when evaluating the potential influence of DGCs on seismic demand, liquefaction triggering, and deformations near embankment structures.
... However, these effects are not well established yet, and more research is needed in this direction. Raymajhi et al. [9] and Kumar and Takahashi [10] investigated the contribution mechanism of shear reinforcement, increment in lateral stress, and drainage effects with the help of three-dimensional finite-element analyses. They reported that the granular columns undergo a shear strain deformation pattern, which is noncompatible with the surrounding soil contrasting with the conventional design assumption of shear strain compatibility. ...
... The granular column and associated ground (Toyoura Sand) is assigned a uniform permeability value of 0.0066 and 0.0002 m/s, respectively. The assigned uniform properties for the granular column is corresponding to (N1) 60cs of 30 (D R~8 0%), per Raymajhi et al. [9] and Khosravifar et al. [20]. The random field of (N1) 60cs values with calibrated parameters of the PDMY02 Model are implemented into the OpenSees numerical model with the help of Matlab code. ...
Chapter
Granular columns have been widely used to mitigate the liquefaction-induced effects on the built environment. Previous studies based on physical and numerical modeling and post-earthquake site investigations consolidate the efficacy of granular columns to mitigate the liquefaction-induced effects under small earthquakes. The increment in lateral stress due to densification, shear reinforcement, and drainage capacity of granular columns are believed to increase the liquefaction resistance of the ground. However, several case histories and recent research development exhibited the limitations of the effectiveness of granular columns under strong earthquakes. Therefore, a series of dynamic centrifuge experiments are carried out to investigate the effectiveness of granular columns in the liquefiable ground under strong ground motion recorded at Hachinohe Port during the 1968 Tokachi-Oki Earthquake. The performance of granular columns is evaluated by examining the evolution of excess pore water pressure, evolution of co-shaking and post-shaking settlement of foundation-structure system. A series of three-dimensional nonlinear stochastic analyses are also carried out using the OpenSees framework with PDMY02 elasto-plastic soil constitutive model to map the reliability of the performance of equally-spaced granular columns. The spatial nonuniformity of the ground should be considered for a reliable engineering assessment of the performance of granular columns which is implemented with stochastic realizations of overburden and energy-corrected, equivalent clean sand, (N1)60cs values using spatially correlated Gaussian random field. The reliability of the performance of the granular column is assessed based on the stochastic distributions of average surface settlement and horizontal ground displacement associated with the degree of confidence.
... Stone columns are considered as an effective liquefaction mitigation measure. The effectiveness of stone column in reducing liquefaction and seismic performance of stone column remediated ground are well documented by conducting field tests (Ashford et al. 2000), centrifuge studies (Adalier et al. 2003;Rayamajhi et al. 2014), and numerical modeling (Asgari, Oliaei, and Bagheri 2013;Elgamal, Lu, and Forcellini 2009;Rayamajhi et al. 2016a;Tang et al. 2015;Tang, Zhang, and Ling 2016). The various parameters affecting the seismic performance of geosynthetic-encased stone columns are also investigated and reported the necessity of confining the discrete gravels with encasement for seismic resilience (Geng et al. 2017;Tang et al. 2015;Tang, Zhang, and Ling 2016). ...
... The lower dissipation of water through the pores of stone column is attributed to the dilation of stone column, thereby disturbing the drainage path. Additionally, the dilation of dense gravel pile under seismic shaking is well stated (Rayamajhi et al. 2016a). This inference is also published in Rashma, Jayalekshmi, and Shivashankar (2021). ...
Article
The effectiveness of pervious concrete column remediation in homogeneous and sandwiched soil strata for mitigating liquefaction-induced lateral spreading is being investigated in this study. The seismic performance of pervious concrete column improved ground is compared with stone column improved ground. The efficacy of pervious concrete column on three types of soil strata in mitigating liquefaction along with the parameters influencing ground lateral deformation such as thickness of sandwiched liquefiable soil layer, permeability of surrounding soil, ground surface inclination, peak ground acceleration and surcharge load are reported. Three-dimensional nonlinear finite element software OpenSeesPL is used to analyze remediated ground with stone column and pervious concrete column inclusions. Liquefaction-induced lateral deformation is found to be lesser in pervious concrete column improved ground in comparison with stone column improved ground. The lateral deformation of pervious concrete column remediated ground is found to be independent of surrounding soil permeability. The pervious concrete column inclusion is found to be a better alternative to stone column in mitigating liquefaction in susceptible soils like loose sand, medium-dense sand, silt strata and sandwiched liquefiable soil deposits.
... Rigid columns like deep cement mixing columns are also used in very soft soils. The seismic performance of conventional stone column improved ground in mitigating liquefaction is extensively reported in literature (Ashford et al. 2000;Elgamal et al. 2009;Asgari et al. 2013;Tang et al. 2015Tang et al. , 2016Rayamajhi et al. 2016a). ...
... Shear strength at zero effective confining pressure ( cohesionless material with 40% relative density.The shear wave velocity of sand strata is considered as 225 m/s. The stone column is modelled as dense cohesionless material with gravel permeability (Elgamal et al. 2009;Tang et al. 2015;Rayamajhi et al. 2016a). Pervious concrete is also modelled as dense cohesionless material with gravel permeability, but with non-linear properties similar to normal concrete. ...
Article
Full-text available
In this paper, the influence of earthquake characteristics on the seismic performance of ground improved with pervious concrete columns in place of conventional stone columns is presented. Two scaled earthquake ground motions with different seismic characteristics are applied to the finite element models of ground with and without column inclusions. Total stress analysis is also conducted and compared with effective stress analysis on maximum response profile along the depth of column improved ground. The study is further extended to sandwiched liquefiable soil deposits of varying thickness. It is noted that the average lateral displacement reduction of the pervious concrete column improved ground is 90% when compared to unimproved sand strata when subjected to two different earthquake excitations. It is found that the generation of excess pore pressure reaches near zero values when the permeability of pervious concrete column is greater than 0.3 m/s irrespective of the characteristics of the earthquake events. From total stress analysis and effective stress analysis, it is observed that for column improved ground, in addition to pore pressure build-up, the maximum response profile is highly influenced by significant duration and frequency of seismic excitation. The pervious concrete column performed better in homogeneous sand deposit as well as sandwiched liquefiable soil of varying thickness when subjected to different seismic excitations with different characteristics.
... Recent studies [10,11,[13][14][15] suggest that the stone column deformation is a combination of flexural and shear modes. Hence, the stone columns are far less effective in reducing shear stresses in surrounding soils than predicted by the shear strain compatibility theory. ...
... The model input parameters are correlated to the standard penetration field test corrected number of blows [27] as seen in Eqs. [13][14][15]. ...
... Generally, = . Rayamajhi et al. [21,22,23,24] ...
... Yee et al. [26] also investigated the effect of saturation ( ) on seismic compression volumetric strain and found that ( ) ≥60% = ( ) =0% (23) Although further verification studies are needed, it is the opinion of the authors that Eq. (22) and Eq. (23) should also be applicable to any liquefaction-induced volume change calculations, i.e., Figure 8 shows a comparison of the calculated liquefaction-induced settlement ( ) using the data from Grid A (SPT-1, pre-grout CPT-1, and post-grout CPT-1A). For comparison, the pre-grout SPT results are also included. ...
Conference Paper
Full-text available
Ground improvement is one method used for liquefaction mitigation. Various ground improvement techniques , such as vibro-compaction, vibro-replacement stone columns and grouting are used in construction to mitigate liquefaction. Varying methods of mitigation have different advantages and limitations. In this paper, the effectiveness of liquefaction mitigation using compaction grouting is evaluated by the comparison of pre-and post-grouting cone penetration testing (CPT) results. Detailed discussions of the factors affecting the evaluation of post-grouting performance of the compaction grout method are made. In the comparison of pre-and post-grout CPT data, a pseudo-sandification phenomenon was noticed. A correction method for this pseudo-sandification phenomenon is proposed. Future research needs and improvements used for liquefaction mitigation using compaction grouting are also discussed.
... R CSR is defined as ratio of CSR in treated ground to untreated ground. The empirical relationship proposed by Rayamajhi et al. 2014Rayamajhi et al. , 2016 has been used for estimation and comparison. The R CSR was estimated using Eq. 4. ...
Article
Full-text available
Soil liquefaction significantly contributes to inducing catastrophic damage to the infrastructures. Different ground improvement methods were used widely to improve the seismic resistance of liquefiable deposits to mitigate liquefaction. Use of granular column technique is a popular and well-recognized improvement technique due to its drainage, shear reinforcement, and densification characteristics. However, studies relating to seismic resistance of stone column-reinforced ground against multiple shaking events were limited. Recent seismic events also have shown the possibility of liquefaction and reliquefaction due to multiple seismic events. Considering this, the performance assessment of the granular column technique in liquefiable soil under repeated shaking events is addressed in this study. The possibility of re-using construction and demolition waste concrete aggregates as an alternative to natural aggregates is also attempted to propose sustainability in ground improvement. For experimental testing, a saturated ground having 40% density was prepared and subjected to sequential incremental acceleration loading conditions, i.e., 0.1 g, 0.2 g, 0.3 g, and 0.4 g at 5 Hz loading frequency for 40 s shaking duration using a 1 g Uni-axial shake table. The efficiency of selected ground improvement was evaluated and compared with untreated ground. The experimental results showed that ground reinforced with granular columns performs better up to 0.2 g shaking events in minimizing pore water pressure and settlement. Possibility of column clogging, and inadequate area replacement ratio (5%) affects the performance of column during repeated shaking. Also, irrespective of improvement in in-situ ground density; continuous generation of pore water pressure due to absence of drainage posing reliquefaction potential in untreated ground under repeated shaking events.
... Among various techniques available (Ghorbani and Rabanifar 2021;Krishnan and Shukla 2021;Seyedi-Viand and Eseller-Bayat 2022;Chavan et al. 2022;Zhang et al. 2024), the implementation of Stone Columns (SCs) has emerged as a cost-effective and widely adopted method to mitigate the risk of liquefaction in saturated sandy deposits (Mitchell et al. 1995;Adalier and Elgamal 2004). The use of gravel drains has captured the attention of numerous researchers, including Noorzad et al. (1997Noorzad et al. ( , 2007, Brennan and Madabhushi (2002), Adalier et al. (2003), , Rayamajhi et al. (2016), Li et al. (2018), Agah Nav et al. (2020), Ardakani et al. (2020), Gholaminejad et al. (2020Gholaminejad et al. ( , 2021, Thakur et al. (2021), Kumar and Takahashi (2022), Chen et al. (2022), Bhochhibhoya et al. (2023), Abdelhamid et al. (2023), Chakraborty and Sawant (2023), Chaloulos et al. (2023), and Sun et al. (2024). The SCs effectively enhance soil density, improve drainage capacity, and provide a shear reinforcement effect to the ground (Shenthan et al. 2003;Zhou et al. 2021). ...
Article
Full-text available
One effective technique for mitigating the earthquake-induced liquefaction potential is the installation of stone columns. The permeability coefficients of stone columns are high enough to cause a high seepage velocity or expedited drainage. Under such conditions, the fluid flow law in porous media is not linear. Nevertheless, this nonlinear behavior in stone columns has not been evaluated in dynamic numerical analyses. This study proposes a dynamic finite element method that integrates nonlinear fluid flow law to evaluate the response of liquefiable ground improved by stone columns during seismic events. The impact of non-Darcy flow on the excess pore pressure and stress path compared to conventional Darcy law has been investigated numerically in stone columns. Furthermore, the effects of different permeability coefficients and stone column depths have been studied under near and far field strong ground motions. The results indicate that the non-Darcy flow increases the excess pore water pressure as high as 100% in comparison to the Darcy flow.
... (18). Finally, the design value of CSR (CSR Design ) of the improved soil was calculated by multiplying the CSR with the S R reduction factor (Eq. 19) [37,38]. ...
Article
The Manisa-Menemen Railway Project, located west of Türkiye was planned to modernize due to improving the transportation infrastructure in its area. Sandy soils with the potential for liquefaction were identified during the site investigation. Considering the project's location in a region with high seismic activity and soil composed primarily of sand units, it is necessary to design a soil improvement methodology to mitigate the risk of liquefaction. Consequently, liquefaction analyses are conducted to design a suitable soil improvement system. A soil improvement method with deep soil mixing (DSM) columns was proposed to prevent related liquefaction problems. The factor of safety against liquefaction, the liquefaction potential index (LI), and the liquefaction severity index (LS) were calculated both for unimproved and improved soil conditions. To design DSM columns more economically, the length of the columns is reduced while still ensuring that they remained within acceptable limits for LI and LS. The performance of the DSM columns was evaluated under dynamic conditions by Finite Element Method. Based on the results obtained from the analysis, the performance of the columns was satisfactory. This study shows that a performance-based design can be used to design DSM columns in liquefiable soils. This approach can help create more efficient and cost-effective solutions for preventing liquefaction.
... At depth or below structures (larger confinement), test results showed that in both cases high excess pore pressures develop in the soil, however, for the improved ground, acceleration attenuation and subsequent strength loss as a result of liquefaction was less severe and slower. More recently, several numerical studies focusing on the response of stone columns were made both as a result of advancements in soil constitutive modeling as well as of the increase in computational power (e.g., [48][49][50][51][52][53][54][55]). The various studies agree that stiffening is the prevailing beneficial mechanism. ...
Article
The seismic performance of an LNG tank on liquefiable soil improved with stone columns is assessed through 3D effective stress time history analyses. The numerical methodology, which is validated against centrifuge tests, uses the Ta-Ger model to capture the complex sand response under earthquake loading while it simultaneously accounts for Soil-Foundation-Structure interaction by incorporating tank inertial response and both convective and impulsive hydrodynamic actions through a system of properly calibrated oscillators. The methodology introduces a novel technique for incorporating the "improvement" effect of the stone columns by means of "equivalent" soil properties calibrated through separate analyses of a representative remediated 3D soil "cell" explicitly simulating the stone columns within the soil. The analyses show that the presence of the stone columns substantially reduces shear deformations in the improved soil. During shaking, tank settlements accumulate through a rocking, downwards ratcheting, mechanism, which is however constrained by the formation of a stable, nonliquefied soil zone below the tank. Post-seismic, reconsolidation settlements, primarily originating from unimproved zones below the stone columns, are also assessed. Once the complex soil behavior-and dynamic load-mechanisms are comprehensively addressed, differential settlements remain well below allowable limits, demonstrating adequate structure performance even under the high design shaking levels.
... YMK'lar üzerinde geçmişte pek çok araştırmacı tarafından vaka analizleri ( [11][12][13][14][15][16]), laboratuvar deneyleri ( [10,17]) ve sayısal analizler ( [18][19][20][21][22][23][24] ...
Thesis
Full-text available
The behavior of liquefiable soils where the seismic damage potential is very high is among the important issues of geotechnical earthquake engineering. The structures located on the liquefiable soils can be severely damaged due to excessive ground deformations during earthquakes. Therefore, in order to reduce the damage that may occur in the superstructure, it is necessary to improve the liquefiable soils and to support the superstructure. Such an improvement can be made in the soil by forming high modulus columns (HMC). With this improvement, high rigidity columns are formed in the soil and the overall stiffness of the soil is increased, so it is aimed that the soil is less deformed and less exposed to seismic effects under seismic loadings. In general, a liquefiable soil has a complex behavior and it exhibits more complex behavior with ground improvement by forming HMCs. Therefore, a good interpretation and evaluation of this complex behavior will cause a more precise determination of the performance of a liquefiable soil improved by high modulus columns under seismic effects. In this study, the behavior of a liquefiable soil improved with HMCs under seismic effects was investigated with numerical analysis and the response of liquefiable soil was investigated by comparing with the unimproved condition. For this purpose, a series of centrifugal experiments in the literature, which have an improved soil profile with HMCs, were numerically modelled and the results of the numerical analysis were validated by the results obtained from the experiments. Numerical modeling was carried out in twodimensional and three-dimensional conditions by using different numerical programs. The behaviors observed from the analysis results were discussed under detailed headings and compared with the findings obtained from the previous studies in the literature. Finally, parametrical analyses were performed by creating a hypothetical liquefiable soil profile. In parametric analyses, factors such as different area displacement ratios, different shear modulus ratios, different slenderness ratios, different input motion amplitudes were taken into consideration and the behavior of HMC under these conditions in liquefiable soils was examined. As a result of the numerical analysis, it is found that in an improved soil profile, no shear strain compatibility between the HMC and the surrounding soil is seen to take place and the seismic shear stress reduction that will occur in the surrounding soil is much more less than the predicted by the assumption of shear strain compatibility. In addition, HMCs formed in loose liquefiable soils caused an increase in PGA values at the ground surface due to the general stiffness increase in the soil profile. As a result, it is recommended that the shear reinforcement mechanism of the HMCs should not be considered as a primary improvement mechanism in cohesionless soils with regard to shear stress reduction. Therefore, it is concluded that, in design, HMCs should be used with great attention and understanding in terms of shear stress reinforcing mechanism in the surrounding soil. This thesis presents a comprehensive numerical analysis output that aims to elaborate the behavior of HMCs under seismic effects formed in a ground having a liquefiable profile in detail and to improve our understanding of the basic reinforcing mechanism of HMCs. The results of numerical analysis indicate that specific site response analyses should be performed in the liquefaction zone that is improved with HMCs and the performance of composite system should be investigated by performing necessary sensitivity analyses. In summary, the overall evaluation of the finite element analysis results obtained in this thesis call into questioning the assumption of shear strain compatibility by analyzing the response of a liquefiable soil improved with HMC. It should be pointed out that, the behavior of HMCs in a liquefiable soil needs to be examined in more detail by performing additional physical and numerical models considering various soil and structure under different input earthquake motion characteristics. The mechanism of liquefiable soils improved with high modulus columns calls for more experimental and field data from case histories.
... The Poisson's ratio of the geosynthetic encasement was selected as 0.1 to simulate the behaviour of woven geotextile (Soderman and Giroud 1995). The installation effect during the stone column construction process was numerically considered by setting the lateral earth pressure coefficient of the stone column as 0.8, according to Rayamajhi et al. (2016). The friction angles of the stone column and the surrounding soil are 42°and 32°, respectively. ...
Article
This paper presents a numerical study to evaluate the contribution of geosynthetic on the shear strength of geosynthetic encased stone column (GESC) under direct shear loading conditions. The backfill soil was characterized using the linearly elastic-plastic Mohr-Coulomb model. The geosynthetic encasement was simulated using linearly elastic liner elements. The interaction between the geosynthetic encasement and soils on both sides was modeled through two interfaces. The three-dimensional numerical model was validated using experimental data from direct shear tests of GESC models. The shear stress-strain response and the development of longitudinal and circumferential strains of GESC during the shear process were first discussed, and then a parametric study was conducted to investigate the effects of various design parameters on the shear strength of GESC and the contribution of geosynthetic. Results indicate that the shear resistance provided by the geosynthetic encasement develops slowly, which depends on the mobilization of tensile strains. At the failure condition, the longitudinal strains are larger than the circumferential strains, which indicates that the longitudinal tensile rupture is more critical for GESC under shear loading. The vertical stress, geosynthetic encasement stiffness, stone column diameter and spacing have the most important influences on the shear strength contribution of geosynthetic encasement.
... The salient features of the dynamic soil response are wellcaptured with advanced constitutive soil models, after calibration with laboratory test results to reproduce soil nonlinearity effects [31][32][33][34]. Several numerical studies have been carried out to evaluate the seismic response of ground improvements in liquefiable soils, considering free field condition [35][36][37][38][39]. Shahir et al. [40] and Bray and Macedo [41] performed parametric site response analyses including soil-foundation-structure interactions to derive analytical formulations that could be used to estimate the liquefaction-induced settlements of shallow foundations underlain by sand layers with various relative densities. ...
Article
Remedial ground densification techniques are widely employed in seismically active regions to mitigate geotechnical hazards and reduce the potential for damage to structures. These techniques can substantially modify the local soil conditions and the seismic site response characteristics of the profile. This study provides a quantitative insight into the local site amplification in remedially densified soils. Parametric site response analyses are performed using various subsoil conditions and extents of ground densification. The free-field site responses obtained with and without ground densification are compared using two-dimensional (2-D) finite element models. The results show that the frequency content of ground motions propagating in densified sites is modified, with a shift of soil response harmonics towards higher frequencies. When a densified crust is implemented with unimproved soft soil layers underneath, the PSAs at the ground surface are generally reduced, at frequencies between 5 and 10 Hz. However, the levels of de-amplification decrease as the depth of ground densification increases. In particular, the densification of the full depth of liquefiable soil layers leads to higher PSAs at the ground surface. The results presented provide a better understanding of the geometry and density of the improved zones that can lead to the amplification of ground surface motions in the frequency range of interest for building response, prior to investigating more complex problems that include soil-structure interaction.
... The square pile spacing arrangement was investigated herein to take advantage of symmetry and because the overall response of the composite system is driven by the area replacement ratio rather than the specific spacing pattern. Due to symmetry and the application of unidirectional ground motions, the timber pile-improved ground was simulated using a half unit cell [5,[17][18][19]. This approach simulates the dynamic response expected for the middle of a wide zone of improved ground, but does not capture the response along the boundaries of the improved zone. ...
Article
Driven timber displacement piles are being increasingly used to densify and reinforce soils against earthquake-induced ground deformations. However, the role of timber piles to reinforce the soils and redistribute cyclic stresses to timber piles has not been established, despite their excellent flexural properties. This study presents a series of dynamic 3D, linear-elastic, numerical simulations set with the unit cell framework to evaluate the role of the tapered timber pile and design variables such as pile length, spacing and relative density on the amplification and stress redistribution possible with this ground improvement technique. The simulations indicate that the depth-dependent shear strain and shear stress redistribution variously depend on the pile length, spacing, relative density, and input motion frequency. Further, the previously-accepted shear strain compatibility assumption developed for stone columns served to greatly overestimate the magnitude in cyclic shear stress reduction. Due to the tapered pile geometry and the depth-varying soil properties implemented, the accuracy of a recently proposed approach to estimate shear stress redistribution to account for column flexure was found to depend on the flexibility of the composite soil-pile system: longer, more flexible piles and lower relative density were predicted more accurately than shorter, stiffer timber piles with higher relative density. In general, the average shear strain ratio between the improved and unimproved soil is most sensitive to pile length, moderately sensitive to relative density, and least sensitive to pile spacing, and the average ratio of shear stress reduction coefficients is most sensitive to pile spacing, moderately sensitive to pile length, and is least sensitive to relative density.
... Initially, based on the 3D linear-elastic¯nite element analyses, Boulanger et al. [2014] showed that such an assumption leads to an overestimation of the shear stress redistribution from the soil to the dense granular columns. The in°uence of parameters such as area ratio, relative sti®ness ratio (a ratio of the shear modulus of the granular column to the shear modulus of the surrounding soil À À À G r Þ, surface pressure (P Þ and characteristics of input motion on the performance of the mitigated soil and foundation system was investigated with a 3D fully coupled nonlinear e®ective stress analysis based on the simplistic unit cell approach of granular column [Rayamajhi et al. 2016]. However, the impact of these parameters was not assessed with due considerations for the overlying structures. ...
Article
Shallow footings are the most preferred foundations for buildings due to low cost and ease of construction. However, under seismic loads, these foundations may suffer excessive settlements, particularly when there is a risk of soil liquefaction. This paper explores the effectiveness of granular columns in mitigating the liquefaction-induced ground deformations under shallow foundations, using FLAC2D program. PM4Sand, a critical state-based bounding surface plasticity model is used to simulate the stress–strain response of sand to cyclic loading. The responses of granular columns are also simulated using the same soil model. Validation of the numerical model is presented against the experimental results of mildly sloping ground. The application of granular column groups resulted in maximum reduction of the settlement of footing by 60% when soil densification is included along with drainage and stress redistribution effects. Though excess pore water pressure is relatively low in treated deposit compared to the untreated deposit, its contribution to the reduction in settlement of footing is found to be minimal.
... More index properties of the model ground (Toyoura sand) and granular columns can be found in Kumar et al. [13]. The assigned properties for the granular column is corresponding to (N1)60cs of 30 (DR ~ 80 %) as suggested by Raymajhi et al. [23]. The calibrated values of the granular column are shown in Table 1. ...
Conference Paper
Elastic response spectra based on the equivalent linear site response method do not account for the nonlinear elastoplastic deformation and complex soil-structure-interaction of liquefiable ground. Seismic demand observed on the foundation-structure system largely depends on the ground deformation rather than the ground surface acceleration for low-frequency content of input shaking for liquefiable ground. However, the attenuation or amplification of input waves primarily governed by the liquefaction extent of the ground. Moreover, inherent soil variability should be taken into account for the reliable engineering judgment of liquefiable ground deformations and associated displacement response spectra. A dynamic centrifuge test is performed to investigate the liquefaction-induced effects on the foundation-structure system treated with granular columns. The centrifuge test results are used to validate the numerical modeling scheme which is carried out using the OpenSees framework with PDMY02 elastoplastic soil constitutive model. Soil variability is implemented with stochastic realizations of overburden and energy-corrected, equivalent clean sand, (N1)_60cs values using spatially correlated Gaussian random field. Three-dimensional finite element simulations are performed for the sufficient number of realizations to map the scale of fluctuation of stochastic displacement spectra. The ground densification due to the installation of granular columns is also incorporated during the numerical simulations. Efforts are made to trace the correlation between spectral displacement and surface settlement of the ground along with the fluctuation in the peak ground displacement. Besides, the implications of the lower frequency content/range of amplified ground surface displacement spectra are also investigated.
... Granular columns have also been used to mitigate the adverse effects of seismic actions. The rapid drainage provided by granular columns has been utilized to reduce liquefaction risks [21,22]. Moreover, Liu and Hutchinson [23] have investigated the prospect of using granular columns as a means of increasing the subgrade reaction in rocking foundations to benefit from structural support and drainage properties of granular columns simultaneously. ...
Article
Ordinary stone columns and Geosynthetic Encased Stone columns are used in remediation of soft soils with low bearing capacities. Primary objective of granular columns is to provide structural support to the overlying foundation layers. Given that the granular columns implemented in soft soil conditions support a large portion of the surcharge pressure, developing an understanding of settlement response and pressure bearing characteristics of granular columns under seismic loading conditions is of paramount importance. This study aims to present experimental findings of granular column load bearing response under simulated seismic loads and the effects of lateral boundary conditions on column behavior. In order to mimic the seismic behavior of columns supporting a sustained surcharge load, two different large-scale experimental assemblies are used in 1-g shaking table tests. The assemblies used were a laminar box and a rigid box which were intended as physical analogies for free-field and rigid boundary conditions. The reinforcement strains, pressure concentration on column heads, and settlement of the unit cells enhanced with granular columns with varying reinforcement stiffness-es are studied. The relationship between unit cell settlement and two important earthquake intensity measures namely, Arias Intensity and Shaking Intensity Rate, are also investigated.
... Mitchell, 2008;Adalier and Elgamal, 2004). However, recent numerical studies by Rayamajhi et al. (2014Rayamajhi et al. ( , 2016 and Green et al. (2008) demonstrated that discrete columns may deform in both flexure and shear, being less effective in reducing shear stresses than what shear stress compatibility implies. Investigations based on vibroseis "T-Rex" and/or cross-hole tests in New Zealand and Ecuador (Wissmann et al., 2015;Smith and Wissmann, 2018) provided evidence that RAP reinforced ground is significantly stiffer than the untreated natural soil. ...
Article
In the engineering geology field increased attention has been posed in recent years to potential liquefaction mitigation interventions in susceptible sand formations. In silty sands this is a major challenge because, as the fines content increases, vibratory methods for densification become progressively less effective. An alternative mitigation technique can be the installation of Rammed Aggregate Pier® (RAP) columns that can increase the resistance of the soil, accounting for its lateral stress increase and for the stiffness increase from soil and RAP composite response. To investigate the influence of these factors on liquefaction resistance, full-scale blast tests were performed at a silty sand site in Bondeno (Ferrara, Italy) where liquefaction was observed after the 2012 Emilia-Romagna earthquake. A multidisciplinary team of forty researchers carried out devoted experimental activities aimed at better understanding the liquefaction process at the field scale and the effectiveness of the treatment using inter-related methods. Both natural and improved areas were investigated by in-situ tests and later subjected to controlled blasting. The blast tests were monitored with geotechnical and geophysical instrumentation, topographical surveying and geological analyses on the sand boils. Results showed the RAP effectiveness due to the improvement of soil properties within the liquefiable layer and a consequent reduction of the blast-induced liquefaction settlements, likely due to soil densification and increased lateral stress. The applied multidisciplinary approach adopted for the study allowed better understanding of the mechanism involved in the liquefaction mitigation intervention and provided a better overall evaluation of mitigation effectiveness.
... Rayamajhi et al. [3] numerical findings question the validity of the strain-compatibility assumption for design. Rayamajhi et al. [5] suggested a better performance when these rigid elements are fixed against rocking and Rayamajhi et al. [6] suggested a modified design equation to estimate the reduction in cyclic stress ratio provided by dense granular columns. This paper presents a case history in Aydin, Turkey, where a composite ground reinforcement system was constructed by GCC, a type of cemented rigid inclusion, and Impact ® RAP stone column elements, recommended to control excessive settlements and a mitigation solution against liquefaction triggering. ...
Chapter
Within the scope of this manuscript, the mitigation performance of a composite ground improvement solution, which is composed of 18 m long 40 cm diameter GeoConcrete® Column (GCC) and 50 cm diameter Impact® Rammed Aggregate Pier® (RAP) along with 40 m long 80 diameter piles is assessed by pre- and post-cone penetration testing (CPT). These elements are designed for controlling excessive total and differential settlements, and liquefaction triggering at a paper mill site. In this paper, the site geology, geotechnical model, design aspects of GCC and Impact® RAP patented systems and QA/QC measures are discussed. As a mitigation solution, 18 m and 40 m long elements are designed to be constructed in the soft to medium stiff silty clay with scattered silt and sand interlayers. Improvement expectations from GCC and Impact® RAP elements are partially verified by pre- and post-CPT data, and are listed as: (i) densification of cohesionless silt and sand layers, (ii) shear stress transfer to rigid columns during cyclic (seismic) loading, reducing seismic demand from foundation soils (iii) increased horizontal stresses, leading to increased soil (and column) stiffness and strength, (iv) vertical drainage through aggregate columns to dissipate cyclically – induced excess pore water pressures. The results show that due to ramming and vibration induced-densification, cone tip resistance has increased by a factor of 1.3–1.6 in cohesionless layers.
... The typical pile-pinning liquefaction mitigation technique implements piles that are arranged in a square or triangular grid pattern, the former with different pile orientations as shown in Fig. 2. The unit cell method is used to model the pile group-improved slope for computational efficiency. This approach is appropriate for simulation of broadly-distributed improvements ranging from pre-fabricated vertical drains [31,32], stone columns [33][34][35][36][37], and deep soil mixed columns [38]. This approach simplifies large volumes of improved ground to a single unit of improvement representative of its tributary area. ...
Article
Recent 1-g shake table experiments have shown that the relatively new X-shaped cast-in-place piles can improve the seismic response of slopes susceptible to lateral-spreading as compared to conventional bored piles when mitigated using the pile-pinning method. This paper presents three-dimensional (3D) nonlinear dynamic numerical simulations of groups of piles with X-shaped cross-sections subjected to lateral spreading to broaden the understanding of their effectiveness in mitigating slope displacements. The unit cell method is used with the stress-ratio controlled and critical state-compatible Dafalias-Manzari model to capture appropriate cyclic behavior of the liquefiable soil surrounding the piles subjected to seismic ground motions. The numerical simulations facilitate the evaluation of various parameters controlling soil-pile interaction and the structural pile response, including the effect of pile spacing, pile fixity, pile orientation, slope angle, and geometrical effects of the pile cross-section with emphasis on the X-shaped section. The results demonstrate that X-shaped pile groups can significantly reduce lateral slope displacements compared to the unimproved or circular pile-improved ground, and that the spacing, pile orientation and pile fixity play a critical role in the deformation response. These findings provide insight to the design of pile-improved ground as well as the structural design of piling adjacent to or within liquefiable slopes.
Article
The use of permeable piles as an effective drainage method in liquefiable sites has become widely accepted. In this study, the seismic response of both the liquefiable soil and the pile was simulated using FLAC3D software to validate the anti-liquefaction performance of the permeable pile. A group of permeable piles designed according to the China foundation code were numerically modeled with various opening ratios (i.e. area of openings/total surficial area). The numerical results showed that the permeable pile is able to enhance liquefaction resistance by dissipating excess pore water through the drainage holes. The bending moments and axial force of the permeable pile decrease but the ultimate bearing capacity increases in the process of drainage. It is found that the excess pore water pressure ratio (EPWPR) of soil around permeable pile under seismic loading reduces rapidly with increasing opening ratio, but the excess pore water pressure tends to keep nearly a stable level once the opening ratio is beyond a critical value of 0.5%. As a result, the critical value of the opening ratio may be considered as the optimum parameter to design the permeable pile against liquefaction.
Article
A series of undrained cyclic triaxial tests were carried out on loose sand specimens, including encased and non-encased granular columns, to evaluate the cyclic behavior and liquefaction resistance of the ground improved by granular columns. It was found that using geogrid encasements could effectively reduce cumulative settlements and mitigate the liquefaction potential when its tensile stiffness was high enough. Another finding was the inefficiency of flexible geosynthetic encasements to delay and mitigate the liquefaction in granular columns with the possibility of clogging. Findings indicated that the improvement of a loose ground with encased granular columns not only decreased the liquefaction-induced ground deformation but also significantly reduced the effect of earthquake magnitude on the ground deformation. It was also found that using the granular column and encasing it with a high-stiffness encasement not only slowed down the rate of ground softening during the cyclic loading experience but also decreased the dissipation of energy.
Article
The existing engineering methodologies for liquefaction mitigation rely on free-field triggering in uniformly layered granular soil deposits. These methods routinely ignore cross-layer interactions in stratified deposits, consequences of softening and various mechanisms of mitigation on building performance, or interactions between and among structures in close proximity of each other. In this paper, through an experimental-numerical study, we show that these methods are unreliable, jeopardizing our ability to assess and mitigate liquefaction vulnerability from building to cluster, and to community scales. Fully-coupled, 3D, dynamic finite element analyses, validated with centrifuge experiments, show that combining ground reinforcement with drainage and densification (e.g., through installation of dense granular columns) can improve foundation’s settlement, but not necessarily to acceptable levels. To achieve desired levels of reduction in settlement, it is critical to minimize the likelihood of clogging in such drains, particularly in the presence of silt interlayers. These methods, however, may increase foundation’s tilt potential, which must be evaluated on a case-by-case basis. Unsatisfactory tilt is often uneconomical to repair, which may lead to the decision to demolish or relocate. And this engineering demand parameter (EDP) becomes particularly difficult to improve in urban settings and in stratified and non-uniform deposits. The combined influence if seismic coupling and stratigraphic variability on mitigation efficacy is shown to be significant in terms of foundation tilt, spectral accelerations, and flexural drifts experienced within the superstructure of both mitigated and unmitigated neighbors. These effects are notable for spacing-to-foundation width-ratios (S/W) as large as 1.0, which are common in cities. Additional measures and technologies may be needed to reduce tilt to acceptable levels in closely-spaced cluster configurations and realistically stratified deposits, while simultaneously strengthening both the ground and structures at an area-level and in a cost-effective and sustainable manner.
Article
Geopier Rammed Aggregate Piers® (RAPs) are a ground improvement technology that creates a densified column of aggregate surrounded by a stiffened matrix soil. This paper describes the design and construction of RAPs at Te Kaha, a $683-million Multi-Use Arena under construction in Christchurch, New Zealand. CLL Projects are constructing 8331 RAPs including 1092 tension RAPs to depths between 5.5 to 12m to provide a ground improvement system supporting the arena. Design considerations include estimation of soil densification in a wide range of soil conditions (sand, silty sand, silt and gravel), analysis of liquefaction triggering before and after ground improvement, numerical analysis to predict the bearing capacity and settlement of the foundations, and prediction of uplift capacity for tension RAPs. The design predictions and the actual results from verification testing are compared, including pre- and post- improvement CPTs and tension load tests. At Te Kaha the RAP installation resulted in a significant increase in penetration resistance of sandy soils between the RAP elements. The CPT results consistently underestimated the fines content of the soil. The tension load test results showed that the uplift capacity is dependent on the soil conditions at the tip of the tension RAP. If adequate confinement cannot be achieved at the base the tension RAP ‘unravels’ and the capacity is much lower than typical design methods would predict.
Article
Rigid inclusions are increasingly being specified in seismic regions to transmit foundation loads to competent strata at depth due to their ability to provide excellent static performance and potential for cost-savings over other forms of ground improvement and/or deep foundations. Despite their widespread application in seismic regions, the seismic kinematic interaction of rigid inclusions is not well understood. This study presents a series of parametric numerical simulations specifically conducted to capture the kinematic soil-rigid inclusion interaction under seismic loading to identify key mechanisms that contribute to seismic performance. The effect of ground motion variability, area replacement ratio, surface crust thickness, embedment into a competent layer, liquefiable layer thickness, and steel reinforcement is systematically investigated. Although the rigid inclusion may not prevent liquefaction triggering, severe amplification associated with dilation spiking of transiently liquefied soil is mitigated and the onset of liquefaction delayed due to the soil-rigid inclusion interaction. The role of static arching to alter the geostatic stress state prior to and during shaking is shown to be responsible for significant and heretofore unknown coupled fluid-mechanical interaction that drives the performance of the rigid inclusion within the reinforced soil system. The kinematic flexural demand following the triggering of liquefaction and phase transformation associated with cyclic mobility is met through transient increases in axial load, which increases the confinement of the grout comprising the rigid inclusion, and therefore its moment capacity. The complex mechanisms identified in this work should be used to help identify which subsurface conditions may lead to responses, guide design decisions regarding selection of reinforcement and embedment, and provide a basis for assessments of the anticipated kinematic demands in view of the beneficial axial load-moment capacity interaction following soil liquefaction.
Chapter
Dense granular columns (DGC) have become a common soil improvement strategy for critical embankment structures founded on potentially liquefiable deposits. The state-of-practice for the design of DGCs is limited to simplified methods that consider, separately, the three-primary liquefaction-mitigation mechanisms provided by these columns: (i) installation-induced densification; (ii) enhanced drainage; and (iii) shear reinforcement. Critical aspects, such as the effects of soil-column-embankment interaction, site characteristics and layer-to-layer interaction, ground motion characteristics beyond the peak ground acceleration, and the total uncertainty, are not included in current engineering design procedures. In this work, we present results from a numerical parametric study, previously validated with dynamic centrifuge test results, to evaluate the liquefaction hazard in layered profiles improved with DGCs. The criteria for various degrees of liquefaction are based on peak excess pore pressure ratios and shear strains observed within each layer. Our study includes different properties and geometries for both soil and DGCs, various confining pressures induced by an overlying embankment, as well as a large collection of ground motions from shallow crustal and subduction earthquakes. We performed a total of 30,000 3D, fully coupled, nonlinear, dynamic finite-element (FE) simulations in OpenSees using a state-of-the-art soil constitutive model (PDMY02), whose properties were calibrated based on both element level laboratory tests and a free-field boundary-value problem modeled in the centrifuge. The results from this parametric study are used to develop a probabilistic predictive model for the triggering of liquefaction in embankment sites treated with DGCs. KeywordsLiquefaction triggeringDense granular columnsFinite-element modelingCentrifuge modelingProbabilistic models
Article
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Both a dynamic centrifuge test and dynamic finite element analysis were carried out to assess the seismic liquefaction risk of a saturated-calcareous-sand site in a port project in Timor-Leste. Taking the in situ calcareous sands as the model material, two groups of horizontal free-field model tests for medium dense and dense saturated calcareous sands were completed based on the two-stage scaling law theory. Three natural earthquake records with varied peak accelerations were adopted as input motions. The experimental results indicate that the shallower the depth, the lower the relative density, the longer the seismic duration, the larger the peak acceleration, and the more susceptible the saturated site to liquefaction. The sands on site at a depth of five to ten meters is highly risky for liquefaction with the excess pore pressure ratio reaching up to about 1.0 under the seismic peak acceleration of 0.3 g. The risk of liquefaction for site sands is rather small under the seismic peak acceleration of 0.1 g. The study reveals the characteristics of the pore pressure development in sites of varied relative densities under different seismic loadings, which provides a scientific basis for the liquefaction risk assessment of the engineering site.
Article
Effective mitigation of seismic-induced ground hazards requires an improved understanding of ground response in terms of earthquake wave propagation and ground deformation. Here, this paper examines the effects of geosynthetic-encased stone columns (ESCs) and ordinary stone columns (SCs) on the acceleration amplitude and frequency content responses of sand profiles, and the deformation of the ground using a large-scale shaking table model test. The model was excited by 15 shaking events including El Centro motion, Wenchuan Qingping motion and Kobe motion with peaks ranging from 0.1 to 0.9 g. The results indicate that the ESCs more significantly amplify surface accelerations compared to the SCs in the frequencies ranging from 10 to 17 Hz and from 2.5 to 9 Hz. The horizontal peak acceleration values in the ESCs composite ground are approximately twice those of the SCs composite ground. The acceleration response of the ground is influenced by the applied acceleration peak and frequency content, reinforced type, and structure. After the seismic excitation, the ESCs composite ground develops much narrower surface cracks distributed in a larger area compared to the SCs.
Conference Paper
This paper presents a case study of an elevated water tank supported by mixed ground improvement techniques, including Vibro-Compaction, Vibro Piers, and Compaction Grouting in East St. Louis, Illinois. An adaptive design approach provided the best-value solution for a complicated set of geotechnical problems, including static bearing capacity and settlement concerns as well as liquefaction-induced settlement. Ground improvement techniques resolved the geotechnical challenges at the site through an adaptive approach, by utilizing real-time data acquisition and progressive rounds of verification to achieve performance objectives. This paper details the evaluation of geotechnical criteria, the selection of ground improvement techniques, as well as the adaptive design and implementation of ground improvements, to ensure that the best value was provided. With the ground improvement, the elevated water tank was able to be built on shallow foundations instead of deep foundations.
Chapter
Bhuj earthquake in 2001 produced an insight into researchers in India to study the liquefaction phenomenon, especially in loose saturated sand deposits. India is a country with plenty of saturated loose deposits of cohesionless soil; thus, there is a need to study the liquefaction characteristics of soils in India. This paper presents a brief review of the liquefaction studies conducted in India, mainly using SPT N values, soil profile data, or medium-sized shake table tests, and noticed that limited studies were done in Kerala. The paper also discusses the various ground improvement techniques available for liquefaction mitigation. Though several traditional methods like densification, drainage mitigation, stabilization, or reinforcement exist to mitigate liquefaction vulnerabilities, recent studies focus on achieving low cost, environmentally friendly, and non-disturbing methods. Since Kerala lies in seismic zone III, more research and development are essential in studying the liquefaction phenomena, highlighting the importance of a ground improvement technology program to select the site-specific techniques.
Article
This paper presents the seismic analysis of stone column (SC) improved liquefiable ground using a three-dimensional (3D) plasticity model with unified description of coarse-grained soil (CGS). The model is a modification of an existing plasticity model for large post-liquefaction deformation of sand, with improvements on the formulation for strength characteristics exhibited by CGS. According to requirements of FLAC 3D User-Defined-Model (UDM), the model is implemented into the finite difference code FLAC 3D , for which a method synchronizing the mapping centres and sharing necessary internal variables of subzones is developed to resolve the computational stability issue caused by the mixed discretization technique of FLAC 3D. The model is validated against monotonic/cyclic and undrained/drain laboratory tests under 8 different stress paths and initial states on a gravel material and Toyoura sand. A centrifuge shaking table test on SC improved liquefiable ground is simulated adopting the model. The results show that the constitutive model and analysis method are effective in reproducing the liquefaction behaviour of CGS ground under seismic loading. Parametric analysis for lique-faction mitigation effects of SCs is further conducted, highlighting the importance of densification and maintaining drainage efficiency of SCs. Results show that the SC's effective improvement area is approximately 2-3 times its diameter.
Conference Paper
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Bu çalışmada, Yeni Zelanda Christchurch’ da yer alan ve yüksek modüllü kolonlarla iyileştirilmiş sıvılaşabilir bir zemindeki iyileştirme öncesinde ve sonrasında oluşan sıvılaşmaya karşı güvenlik sayıları literatürde yer alan kayma şekil değiştirmesi uyumluluğu ve uyumsuzluğu kabulleri kullanılarak hesaplanmıştır. Çalışma içerisinde, yapılan kabullerin esaslarına değinilerek her iki yöntemin eksik kısımlarından bahsedilmiştir. Ayrıca, bu kabullere göre ilgili bölgede zemindeki sıvılaşmaya karşı güvenlik sayıları hesaplanarak her iki yöntemin karşılaştırılması yapılmıştır. Kullanılan yöntemler sonucunda yapılan karşılaştırmalardan elde edilen güvenlik sayılarının oldukça farklı çıktığı görülmüştür ve bu farklılığın uygulamadaki karşılığı üzerine değerlendirmeler yapılmıştır. Özellikle günümüzde uygulamada kayma şekil değiştirmesi uyumluluğu baz alınarak yüksek modüllü kolonlarla iyileştirilmiş bir zeminin sıvılaşma hesabı yapıldığı göz önüne alındığında, çalışma kapsamında elde edilen sonuçların yararlı olacağı düşünülmektedir.
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This paper presents the result of two-dimensional fi nite element modeling studies in order to investigate the seismic behavior of high modulus columns in liquefi able soil. Particular attention was paid to the shear stress reduction mechanism of the high modulus columns and the shear strain distribution between soil and columns during earthquake motion. Numerical analyses were performed using a nonlinear elasto-plastic model in Plaxis 2016. The reliability of the numerical simulations was verifi ed through the results of a centrifuge test model designed to investigate the contribution of high modulus columns in liquefaction mitigation. The capability of numerical simulations was assessed primarily through comparison of predicted acceleration-time histories, pore water pressures, and displacements with the measured counterparts. The results of the numerical analysis showed that the presence of the columns did not reduce seismic shear stresses in the soil when compared to the unimproved soil condition and pure shear behavior between soil and column did not develop as expected in the current design methodology.
Conference Paper
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The installation of stone columns or piers in a loose, saturated sand deposit can potentially mitigate the risk of liquefaction by decreasing the seismic demand on the soil by redistributing the induced shear stresses from the sand to the columns or piers. In calculating the shear stress redistribution, it is commonly assumed that both the soil and the columns or piers respond as shear beams. Although less common, it has also been assumed that the soil responds as a shear beam and that the columns or piers respond as flexural beams, with the redistribution of the shear stresses computed accordingly. However, the results presented herein show that the columns or piers, and the soil immediately surrounding the column/pier, deform in a combination of shear and flexure. The percent contribution of shear versus flexural deformation of the column or pier varies with depth, with the column/pier deforming predominantly in flexure near the ground surface and predominantly in shear at depth. The percent contribution of each mode of deformation governs the redistribution of the shear stresses from the soil to the pier. The distribution of the shear stresses between the soil and columns or piers are quantified for "typical" properties of a loose, saturated sand profile reinforced with Impact TM Rammed Aggregate Piers TM .
Article
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Vibro stone column is a proven technique to mitigate liquefaction and its consequences in saturated sandy soils. This technique relies mainly on three mechanisms: (a) densification of insitu soil during installation, (b) reinforcement, and (c) drainage during an earthquake to hinder excess pore pressure development. However, its effectiveness is limited in low-permeable silty soils that are prone to liquefaction. Composite stone column technique is a recent modified vibro-stone column technique with supplementary wick drains to enhance densification of such silty soils, and thereby, mitigate liquefaction-induced hazards. In this technique, wick drains are pre-installed at midpoints between designated stone column locations. Wick drains aid dissipation of excess pore pressure induced during installation enhancing further densification. This paper presents a numerical model to simulate, and to analyze soil densification during composite stone column installation. Numerical results for densification performance of composite stone column during installation are presented and compared with field performance data. Key soil parameters that limit the effectiveness of composite stone columns for densification during installation are identified.
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The behaviour of all geomaterials, and in particular of soils, is governed by their interaction with the pore fluid. The mechanical model of this interaction when combined with suitable constitutive discription of the solid phase and with efficient, discrete, computation procedures, allows most transient and static problems involving deformations to be solved. This paper describes the basic procedures and the development of a general purpose computer program (SWANDYNE-X). The results of the computations are validated by comparison with experimental results obtained on physical models tested in the Cambridge Centrifuge.
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Finite-element (FE) simulations are increasingly providing a versatile environment for conducting lateral ground deformation studies. In this environment, mitigation strategies may be assessed in order to achieve economical and effective solutions. On the basis of a systematic parametric study, three-dimensional FE simulations are conducted to evaluate mitigation by the stone column (SC) and the pile-pinning approaches. Mildly sloping saturated cohesionless strata are investigated under the action of an applied earthquake excitation. For that purpose, the open-source computational platform OpenSees is employed, through a robust user interface that simplifies the effort-intensive pre- and postprocessing phases. The extent of deployed remediation and effect of the installed SC permeability are investigated. The influence of mesh resolution is also addressed. Generally, SC remediation was found to be effective in reducing the sand stratum lateral deformation. For a similar stratum with permeability in the silt range, SC remediation was highly ineffective. In contrast, pile pinning appeared to be equally effective for the sand and silt strata permeability scenarios. Overall, the conducted study highlights the potential of computations for providing insights toward the process of defining a reliable remediation solution.
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Object composition offers significant advantages over class inheritance to develop a flexible software architecture for finite-element analysis. Using this approach, separate classes encapsulate fundamental finite-element algorithms and interoperate to form and solve the governing nonlinear equations. Communication between objects in the analysis composition is established using software design patterns. Root-finding algorithms, time integration methods, constraint handlers, linear equation solvers, and degree of freedom numberers are implemented as interchangeable components using the Strategy pattern. The Bridge and Factory Method patterns allow objects of the finite-element model to vary independently from objects that implement the numerical solution procedures. The Adapter and Iterator patterns permit equations to be assembled entirely through abstract interfaces that do not expose either the storage of objects in the analysis model or the computational details of the time integration method. Sequence diagrams document the interoperability of the analysis classes for solving nonlinear finite-element equations, demonstrating that object composition with design patterns provides a general approach to developing and refactoring nonlinear finite-element software.
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This manual focuses on the needs of engineers involved in the geotechnical design of foundations for transmission line structures. It also will serve as a useful reference for other geotechnical problems. In all foundation design, it is necessary to know the pertinent parameters controlling the soil behavior. When it is not feasible to measure the necessary soil parameters directly, estimates will have to be made from other available data, such as the results of laboratory index tests and in-situ tests. Numerous correlations between these types of tests and the necessary soil parameters exist in the literature, but they have not been synthesized previously into readily form in a collective work. This manual summarizes the most pertinent of these available correlations for estimating soil parameters. In many cases, the existing correlations have been updated with new data, and new correlations have been developed where sufficient data have been available. For each soil parameter, representative correlations commonly are presented in chronological order to illustrate the evolutionary development of the particular correlation. The emphasis is on relatively common laboratory and in-situ tests and correlations, including those tests that are seeing increased use in practice.
Article
Dense granular columns can be used to mitigate liquefaction hazards through a combination of densification, increases in lateral stress, reinforcement, and drainage effects. Three-dimensional (3D) nonlinear dynamic finite-element analyses are used to examine the effectiveness of dense granular columns for reducing liquefaction-induced deformations in the event that the triggering of liquefaction in the native soils is not prevented. The finite-element analyses consider unit cells with dense granular columns (improved case) and without granular columns (unimproved case). Parametric analyses are used to isolate aspects related to the different improvement mechanisms. The parametric studies consider a range of area replacement ratios, shear modulus ratios, diameter of granular columns, liquefiable soil depth, hydraulic conductivity, surface pressures, slope angle, penetration resistances in the native soil, and spatial variations in those penetration resistances. A set of 10 acceleration time histories were used as input motions. Dense granular columns were shown to be effective in reducing lateral spreading displacements of sloping ground, even if liquefaction triggering is not prevented. The reductions in lateral spreading displacement are primarily attributable to the reinforcing and strengthening effects of the granular columns, with drainage being a secondary benefit for cleaner sand profiles. The effect of spatially varying penetration resistances as develops around a column are examined and recommendations are developed for selecting an equivalent uniform value for design.
Article
The drainage capacity of stone columns or gravel drains for mitigating liquefaction hazards is evaluated. Recent construction experiences show that the effective permeability of a stone column is greatly affected by construction procedures. Recent improvements in the analysis of drainage columns show that the pioneering work of Seed and Booker, still widely referenced in U.S. practice, greatly underestimates the detrimental effects of vertical drain resistance. These and other aspects related to the drainage capacity of stone columns or gravel drains are discussed.
Article
This paper presents a case history of vibro-replacement stone column design, prediction, installation monitoring, and post improvement compliance testing for a building complex consisting of eight, 5- and 6-story, over-parking buildings. The site provided construction challenges resulting from marginal subsoil conditions of previously reclaimed land, space limitations, project time constraints, and disposal of excess water within acceptable environmental standards. A geotechnical exploration program consisting of Standard Penetration Test (SPT) borings and Piezocone Penetration Test (PCPT) soundings indicated subsoil conditions, in-situ strength, and classification characteristics ideally suited for the vibro-replacement method of ground improvement and reinforcement. Evaluation and cost comparison of a pile foundation, vibro-replacement and spread footings confirmed the economic advantage of in situ ground improvement by the installation of vibro-replacement stone columns.
Article
Significant factors affecting the liquefaction (or cyclic mobility) potential of sands during earthquakes are identified, and a simplified procedure for evaluating liquefaction potential which will take these factors into account is presented. Available field data concerning the liquefaction or nonliquefaction behavior of sands during earthquakes is assembled and compared with evaluations of performance using the simplified procedure. It is suggested that even the limited available field data can provide a useful guide to the probable performance of other sand deposits, that the proposed method of presenting the data provides a useful framework for evaluating past experiences of sand liquefaction during earthquakes and that the simplified evaluation procedure provides a reasonably good means for extending previous field observations to new situations. When greater accuracy is justified, the simplified liquefaction evaluation procedure can readily be supplemented by test data on particular soils or by ground response analyses to provide more definitive evaluations.
Article
Discrete columns, such as stone and soil-cement columns, are often used to improve the liquefaction resistance of loose sandy ground potentially subjected to strong shaking. The shear stress reduction in the loose ground resulting from the reinforcing effect of these stiffer discrete columns is often considered as a contributing mechanism for liquefaction mitigation. Current design practice often assumes that discrete columns and soil deform equally in pure shear (i.e., shear strain-compatible deformation). In addition, because the discrete column is stiffer than the soil, it is assumed to attract higher shear stress, thereby reducing the shear stress in the surrounding soil. In this paper, shear stress reduction in liquefiable soils and shear strain distribution between liquefiable soil and discrete columns along with the potential of development of tensile cracks is investigated using three-dimensional linear elastic, finite-element analysis. Parametric analyses are performed for a range of geometries, relative stiffness ratios, and dynamic loadings. These linear elastic results provide a baseline against which future nonlinear modeling results can be compared, but they are also sufficient for demonstrating that shear stress reductions are far less than predicted by the assumption of shear strain compatibility. These numerical results are consistent with those of other researchers and further call into question the appropriateness of the strain-compatibility assumption for design.
Conference Paper
Ground improvement using stiff columnar reinforcement, such as stone, jet-grout, and soil-mix columns, is commonly used for mitigation of seismic damage in weak ground. Seismic shear stress reduction in the reinforced soil mass is often counted on for reducing liquefaction potential. Current design methods assume composite behavior of the reinforced soil, where the shear stress reduction is based on the ratio of the columnar stiffness relative to the soil as well as the area, replacement ratio. This implicitly assumes the stiff columns will deform in pure shear along with the soil. We performed 3-D dynamic finite element modeling to better understand the column deformation and shear stress reduction behavior. We found that the columns deform in both shear and flexure, providing little seismic shear stress reduction and current methods may be unconservative.
Article
In saturated clean medium-to-dense cohesionless soils, liquefaction-induced shear deformation is observed to accumulate in a cycle-by-cycle pattern cyclic mobility. Much of the shear strain accumulation,occurs rapidly during the transition from contraction to dilation near the phase transformation,surface,at a nearly constant low shear stress and effective confining pressure. Such a stress state is difficult to employ as a basis for predicting the associated magnitude of accumulated permanent shear strain. In this study, a more convenient,approach,is adopted,in which,the domain,of large shear strain is directly defined by strain space parameters. The observed cyclic shear deformation is accounted for by enlargement and/or translation of this domain in deviatoric strain space. In this paper, the model,formulation,details involved,are presented,and,discussed. A calibration phase,is also described,based,on data from,laboratory sample,tests and dynamic,centrifuge experiments,for Nevada sand at a relative density of about 40%. DOI: 10.1061/ASCE1090-02412003129:121119 CE Database subject headings: Liquefaction; Constitutive models; Cyclic plasticity; Soil dynamics; Centrifuge models.
Article
A simplified procedure using shear-wave velocity measurements for evaluating the liquefaction resistance of soils is presented. The procedure was developed in cooperation with industry, researchers, and practitioners and evolved from workshops in 1996 and 1998. It follows the general format of the Seed-Idriss simplified procedure based on standard penetration test blow count and was developed using case history data from 26 earthquakes and >70 measurement sites in soils ranging from fine sand to sandy gravel with cobbles to profiles including silty clay layers. Liquefaction resistance curves were established by applying a modified relationship between the shear-wave velocity and cyclic stress ratio for the constant average cyclic shear strain suggested by R. Dobry. These curves correctly predicted moderate to high liquefaction potential for >95% of the liquefaction case histories and are shown to be consistent with the standard penetration test based curves in sandy soils. A case study is provided to illustrate application of the procedure. Additional data are needed, particularly from denser soil deposits shaken by stronger ground motions, to further validate the simplified procedure.
Article
The results presented were developed as part of a larger project analyzing the behavior of full-scale laterally loaded piles in liquefied soil, the first full-scale testing of its kind. Presented here are the results of a series of full-scale tests performed on deep foundations in liquefiable sand, both before and after ground improvement, in which controlled blasting was used to liquefy the soil surrounding the foundations. Data were collected showing the behavior of laterally loaded piles before and after liquefaction. After the installation of stone columns, the tests were repeated. From the results of these tests, it can be concluded that the installation of stone columns can significantly increase the density of the improved ground as indicated by the cone penetration test. Furthermore, it was found that the stone column installation limited the excess pore pressure increase from the controlled blasting and substantially increased the rate of excess pore pressure dissipation. Finally, the stone columns were found to significantly increase the stiffness of the foundation system by more than 2.5 to 3.5 times that in the liquefied soil. This study provides some of the first full-scale quantitative results on the improvement of foundation performance due to stone columns in a liquefiable deposit.
Article
Full-scale testing of a large pile group is economically not feasible. A concept based on a periodic boundary has been used to study lateral behavior of a large pile group. The approach and findings from anchorage design of a major suspension bridge in California are presented here. Using the repeating nature of soil's displacement field within infinite number of piles arranged in a regular grid pattern, soil-pile interaction phenomenon from the finite area enclosed by one periodic soil boundary effectively represents behavior of the entire pile group. A 3D finite-element analysis was used to create the soil-pile models in which the boundary conditions mimic the repeating nature of the infinite number of piles by slaving the boundary nodes. The soil resistance, as calculated from the finite-element method employing the periodic boundary, is compared with the empirical p-y curve approach for a single isolated pile to determine the group effects. Values of p-multiplier and y-multiplier have been obtained for different pile spacings.
Article
Two of the most important parameters in any dynamic analysis involving soils are the shear modulus and the damping ratio. Because both shear modulus and damping are strain dependent, curves must be developed to define their variation with shear strain. Fifteen studies (including this one) now provide results from tests on a wide variety of gravels. This paper combines the results of available investigations to develop best-fit relationships between (1) shear wave velocity and equivalent N60 from Becker penetration tests; (2) normalized shear modulus and shear strain; and (3) damping ratio and shear strain. The mean curve for the normalized shear modulus reported for gravelly soil in this study falls near the mean curve reported for sands by Seed and Idriss (1970). The normalized shear modulus curve is dependent on confining pressure, but essentially independent of sample disturbance, relative density, and gradation. The mean damping ratio curve falls toward the lower range of the data reported by Seed and Idriss (1970). The damping ratio curve is dependent on confining pressure but essentially independent of other factors.
Article
This paper contains ground-motion prediction equations (GMPEs) for average horizontal-component ground motions as a function of earthquake magnitude, distance from source to site, local average shear-wave velocity, and fault type. Our equations are for peak ground acceleration (PGA), peak ground velocity (PGV), and 5%-damped pseudo-absolute-acceleration spectra (PSA) at periods between 0.01 s and 10 s. They were derived by empirical regression of an extensive strong-motion database compiled by the "PEER NGA" (Pacific Earthquake Engineering Research Center's Next Generation Attenuation) project. For periods less than 1s , the analysis used 1,574 records from 58 mainshocks in the distance range from 0 km to 400 km (the number of available data decreased as period increased). The primary predictor variables are moment magnitude M, closest horizontal distance to the surface projection of the fault plane RJB, and the time-averaged shear-wave velocity from the surface to 30 m VS30. The equations are applicable for M =5-8 , RJB 200 km, and VS30= 180- 1300 m / s. DOI: 10.1193/1.2830434
Article
In many cases densification with vibro-stone columns cannot be obtained in non-plastic silty soils. Shear stress re-distribution concepts [1] have been previously proposed as means to assess stone columns as a liquefaction countermeasure in such non-plastic silty soils. In this study, centrifuge testing is conducted to assess the performance of this liquefaction countermeasure. Attention is focused on exploring the overall site stiffening effects due to the stone column placement rather than the drainage effects. The response of a saturated silt stratum is analyzed under base dynamic excitation conditions. In a series of four separate model tests, this stratum is studied first without, then with stone columns, as a free-field situation, and with a surface foundation surcharge. The underlying mechanism and effectiveness of the stone columns are discussed based on the recorded dynamic responses. Effect of the installed columns on excess pore pressures and deformations is analyzed and compared. The test results demonstrate that stone columns can be an effective technique in the remediation of liquefaction induced settlement of non-plastic silty deposits particularly under shallow foundations, or vertical effective stresses larger than about 45 kPa (1000 psf) in free field conditions.
Article
Cyclic mobility is exhibited by saturated medium to dense cohesionless soils during liquefaction, due to soil skeleton dilation at large shear strain excursions. This volume-shear coupling mechanism results in phases of significant regain in soil shear stiffness and strength, and limits the magnitude of cyclic shear deformations. Motivated by experimental observations, a plasticity model is developed for capturing the characteristics of cyclic mobility. This model extends an existing multi-surface plasticity formulation with newly developed flow and hardening rules. The new flow rule allows for reproducing cyclic shear strain accumulation, and the subsequent dilative phases observed in liquefied soil response. The new hardening rule enhances numerical robustness and efficiency. A model calibration procedure is outlined, based on monotonic and cyclic laboratory sample test data.
Article
A simple elastic-plastic constitutive model for cohesionless soils is proposed. The model retains the extreme versatility and accuracy of the simple multi-surface J2-theory in describing observed shear nonlinear hysteretic behaviour, shear stress-induced anisotropy; and reflects the strong dilatancy dependency on the effective stress ratio. The theory is applicable to general three-dimensional stress-strain conditions, but its parameters can be derived entirely from the results of conventional laboratory soil tests. A number of examples are presented including an analysis of seismically induced liquefaction behind a retaining structure.
Article
Thesis (Ph. D.)--University of Wales, 1988. Includes bibliographical references (p. 349-368).
Analysis and design for inelastic structural response of extended pile shaft foundations in laterally spreading ground during earthquakes
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San Diego on 03/17/16. Copyright ASCE. For personal use only; all rights reserved
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