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Experimental and theoretical studies on the ultimate bearing capacity of geogrid-reinforced sand
Abstract
Geosynthetic reinforced soil (GRS) structures have gained popularity in replacing concrete rigid piles as abutments to support medium or small-spanned bridge superstructures in recent years. This study conducted 13 model tests to investigate the ultimate bearing capacity of the GRS mass when sand was used as backfill soil. The GRS mass was constructed and loaded to failure under a plane strain condition. Test results were compared with two analytical solutions available in literature. This study also proposed an analytical model for predicting the ultimate bearing capacity of the GRS mass based on the Mohr-Coulomb failure criterion. The failure surface of the GRS mass was described by the Rankine failure surface. The effects of compaction and reinforcement tension were equivalent to increased confining pressures to account for the reinforcing effects of the geosynthetic reinforcement. The proposed model was verified by the results of the model tests conducted in this study and reported in literature. Results indicated that the proposed model was more capable of predicting the ultimate bearing capacity of the GRS mass than the other two analytical solutions available in literature. The proposed model can be used to predict the ultimate bearing capacity of GRS structures when sand was used as backfill material. In addition, a parametric study was conducted to investigate the effects of friction angle of backfill soil, reinforcement spacing, reinforcement strength, and reinforcement stiffness on the ultimate bearing capacity of the GRS mass calculated with and without compaction effects. Results showed that the ultimate bearing capacity of the GRS mass was significantly affected by the friction angle of backfill soil, reinforcement spacing and strength. Compaction effects resulted in an increase in the ultimate bearing capacity of the GRS mass.
... The study focuses on the load-carrying capacity of a footing constructed on sandy soil reinforced with geotextile inclusion. Experimental testing was conducted on the geosyntheticreinforced soil beneath a strip footing, following a series of physical modeling experiments conducted by Xu et al. [21]. The testing setup was designed to observe the behavior of the soil. ...
... These influencing aspects mostly consist of the reinforcement layout parameters and attributes, the footing size and shape, the type of load, and the soil bed characteristics. Recently, researchers [20,21,36] have compared the bearing pressure-settlement ratio response curves of reinforced and unreinforced foundations to examine the effect of various parameters on the bearing properties of foundations. ...
... The final load-carrying capacity was defined using the breakpoint approach in this study. The behavior of the medium-dense sandy soil is initially in an elastic state when the settlement ratio reaches s/B = 2%, in which the pressure limit is 150 kPa, as indicated in Fig. 4, according to previous research [7,21]. ...
In this study, a series of small-scale physical model tests were conducted to investigate the effects of fully wrapped geogrid sheets on the load‒settlement response of medium-dense sandy soil beneath a single-strip foundation. Recent research has provided evidence of how different parameters affect the behavior of dense sandy soil when reinforced with fully wraparound geogrid sheets. Additionally, a parametric analysis was conducted to investigate the influence of various factors on the system. These factors include the presence of a folded geogrid sheet, the depth and length of an embedded wraparound geogrid sheet, the thickness of the fully wrapped geogrid layer, the impact of tensile strains along the geogrid sheet, and the effect of additional confinement pressure. The inclusion of a single sheet of full wraparound geogrid sheets has been found to significantly affect the pressure-bearing capacity of medium-dense sandy soil and settlement beneath the strip footing. The carrying capacity increases by 280%, and the settlement ratios decrease by 50% when using one layer of full wraparound geogrid. Moreover, when using one fully folded geogrid sheet, the strain induced beneath the center of the footing decreases significantly by approximately 45.5% and the applied pressure by approximately 15.5% in comparison with two inclusions of planar geogrid layers. In addition, the stress distributions are spread over a larger region within the soil mass. One significant finding is that the presence of two overlapping parts prevents the rupture of the geogrid sheet, as opposed to the planar geogrid sheet.
... whereε m andε D are the soil cell generalized average strain and generalized equivalent strain that consider the strain gradient, respectively;p andq are the soil cell generalized average stress and generalized equivalent stress that consider the strain gradient, respectively; and K and G are the strain gradient bulk modulus and strain gradient shear modulus of the soil cell, respectively. According to Eqs. (37) and (38), one may find: (42) are derived from the approximate linear relationship between stress and strain before yielding and are suitable to the condition q ≤ q s . When the soil is in the yielding state, the stress-strain relationship is no longer linear, and the equation for calculating the stress after the soil has yielded needs to be modified. ...
... The traditional MCSC can be expressed as follows [42]: ...
Soil is a multi-scale granular material and has dramatic particulate and structural characteristics. Soil particles are divided into matrix and reinforcing particles to establish a multi-scale soil cell model according to the mechanical effect generated by the interaction between soil particles at various scales and the physical mechanism at different structural levels of soil. A multi-scale Mohr–Coulomb strength criterion (MCSC) that accounts for the particle size of soil is proposed by using the soil cell model. A series of soil cell samples are prepared to conduct consolidated and undrained tri-axial compression test to determine the model parameters. The yield locus of the multi-scale MCSC is drawn on the deviatoric plan based on the theoretical analysis and test results. Results show that the yield locus of the multi-scale MCSC is also hexagonal and expands with the decrease in the size of the reinforcing particle and the increase in the volume fraction of these particles. In this regard, the multi-scale MCSC can relate the microscopic physical details of soil to its macroscopic shear strength.
... Thus, geotextiles have become a subject of scientific research in recent years. Moreover, they have gained widespread use as reinforcements in stabilizing various engineering structures, including footing, slopes, embankments, retaining walls, culverts, buried structures, and road construction over poor soils [24,38,39]. ...
... The reduction in displacement and stress observed when using geotextile is attributed to the phenomenon of redistribution of the applied load over a larger area of the corrugated steel structure as it undergoes subsequent loading. Such behavior demonstrates the interaction of the soil with the corrugated steel structure, as evidenced by previous studies [38,45]. ...
Geotextiles have become a subject of scientific research in recent years due to their ability to reduce pressure on soil masses and buried structures. However, the effective optimal of geotextiles above the crown of the shell of a soil-steel composite structure (SSCS) is not well described in the literature. This article presents an analysis of the impact of geotextile placement at different locations in the ground cover over the crown of the shell on the behaviour of the steel shell. The tests were carried out under different static loads. In the article, a comparative analysis of the results obtained on a natural scale with those obtained using the finite element method (FEM) is presented. For the purpose of the analysis, an experimentally verified computational model was developed and implemented in the commercial FE code, namely, the Zsoil numerical programme. The result demonstrated a significant reduction in maximum displacements and stresses upon employing a single-layer geotextile. The most significant reduction in vertical displacement, amounting to 37%, was observed when the geotextile was positioned at a shallower depth, closer to the load's zone of influence. Furthermore, it was found that vertical displacements in the crown can be reduced by up to 40% with the application of a double layer of geotextile. Furthermore, analysis of the effect of the position of the geotextile layer revealed that reinforcement is more effective when placed at a shallower depth, closer to the zone of influence of the load. These findings provide valuable information for designers who want to optimise geotextile placement for enhanced performance in SSCS designs.
... In general, the numerical result shows that the load-carrying capacity increases with the increase of the reinforcement strength but decreases with the increase of the reinforcement spacing; hence, using a closer reinforcement spacing allows the use of a reduced reinforcement strength. This finding is in agreement with the result obtained, for examples, by Leshchinsky [43], who found that the spacing between the reinforcement layers could have a major impact on the bearing capacity of an MSE wall-supported footing, and by Xu et al. [44] who found that the load-carrying capacity of a GRS mass was affected by the reinforcement spacing and the reinforcement strength. In Figure 6, the analytical load-carrying capacity was obtained using Equation (1), which was proposed by Wu and Pham [30]; in this equation, the confining pressure σ c used was 34 kPa, the largest particle size d max was 33 mm, the angle of internal friction of the backfill-required for calculating the coefficient of Rankine passive earth pressure K p -was 50 • , and the apparent cohesion c was 70 kPa. ...
... The load-carrying capacity was found to be proportional to the angle of internal friction, but inversely proportional to the vertical spacing. This numerical finding agrees with the results of Xu et al. [44], in which they concluded that the angle of internal friction of the backfill had a significant effect on the load-carrying capacity of the GRS mass. The numerical result was also compared to the analytical result calculated using Equation (1); both the numerical and analytical results showed the same trend of a nonlinear relation on the load-carrying capacity for the values of the angle of internal friction considered here. ...
There is an increasing awareness on the major benefits of using soil-geosynthetic composite (SGC) to achieve and maintain the stability of earth-filled embankment. Unlike the mechanically stabilized earth wall, the mechanism of the composite mass is still not fully understood. For examples, current analyses have been limited to an SGC mass with a reinforcement spacing Sv of 0.2 m only; the combined effect of reinforcement and backfill properties is rarely studied; the equation for the estimation of the load-carrying capacity of the SGC mass has only been validated for backfill with maximum particle size dmax between 10 mm and 33 mm and an Sv/dmax ratio between 6 and 20. The consequences of backfill compaction on an SGC mass with different reinforcement spacings are yet to be validated and whether the load-carrying capacity equation would still be applicable for materials with properties falling outside the above ranges. Through the simulation and validation of a field scale SGC mass, this study aims to assess the influence of various reinforcement and backfill parameters on the mechanical responses of a large-scale experimental SGC mass under its working load and failure conditions; the results are presented in terms of the wrapped face lateral displacement, reinforcement axial strain, and load-carrying capacity.
... In the past few decades, a range of geosynthetic materials, such as geotextile, geocell, geogrid, etc., have found successful applications in soil reinforcement. These materials have proven effective in improving bearing capacity, minimizing settlement, enhancing shear strength, and increasing the frictional angle, showcasing their versatility in geotechnical applications (Adams & Collin, 1997;Ansari & Roy, 2023a;Das et al., 1994;Mittal & Shukla, 2020;Palmeira, 2010;Patra et al., 2005;Sitharam & Sireesh, 2004;Xu et al., 2019). A geocell is a three-dimensional structure designed to provide comprehensive confinement to infilled materials. ...
Large quantities of scrap tires are produced by the automobile industry each year, which causes disposal challenges and impacts the environment. However, scrap tires exhibit various properties, including tensile strength, abrasion resistance, durability, thermal conductivity, elasticity, and more. Due to their versatile characteristics, these scrap tires can be utilized as construction materials for various civil engineering works to reduce their negative environmental effects and conserve natural resources. This study aims to understand the shear strength behaviours exhibited by geocell-reinforced mixtures of rubber and sand through the unconsolidated undrained triaxial test. Various parameters, including rubber sizes (425 μm to 12 mm), rubber contents (10% to 40% by volume), confining pressures (50 to 300 kPa), and geocell heights (0.2H to 0.8H, where H is the height of triaxial sample), were systematically examined to understand their impact on shear strength characteristics. The experimental findings reveal that deviatoric stress is enhanced with increasing confining pressure and rubber sizes. The maximum benefits of the rubber-sand mixture were observed at 30% rubber content. Geocell-reinforced rubber sand mixture has a higher shear strength with respect to the unreinforced mixture. Furthermore, the energy absorption capacity of the geocell-reinforced rubber sand mixtures was much better as compared to either the clean sand or rubber-sand mixture. The findings of this research demonstrate that geocellreinforced rubber sand mixtures are suitable for various geotechnical engineering works.
... The maximum viability on the bearing capacity enhancement was noticed for a single-layer reinforcement. Compaction resulted an improvement in the ultimate bearing capacity of the geogrid reinforced soil mass (Xu et al. 2019). Reinforcing materials used are woven geotextiles, placed at single and triple layers of pond ash embankment (Vijayasri et al. 2020) and observed useful for its various geotechnical applications. ...
This study aims to investigate polymeric geogrid’s possibility in improving the maximum load-carrying capacity of strip footings lying on the pond ash. Model tests were carried out in a tank of 12 mm thick side plates fitted inside a rigid mild steel frame. The internal dimensions of the tank were 750 mm (length) × 300 mm (breadth) × 400 mm (depth). The factors considered here are the depth of the geotextile layer, the width of the geotextile layer, and the number of layers of reinforcing material (NL). It is observed that the bearing capacity ratio (BCR) values showed an increasing trend with an increase in b/B at all the settlement ratios. Also, there is a large decrease in the BCRs values for FP (fine pond ash) with an increase in the settlement ratios of the polymeric geogrids. With an increase in the number of reinforcement layers, BCR values rise sharply at all settlement ratios. The outcomes of the experiment divulged that the reinforcement significantly influenced the pond ash. From the cost analysis, it is concluded that pond ash reinforced with polymeric geogrid is a cost-effective material for the construction of filling for low-lying areas.
... Considering the regional restriction and limited traffic conditions, geosynthetics reinforcement technology is widely used in road construction with low cost and high construction efficiency [3,4]. Many scholars conducted a large number of studies on the characteristics of reinforced soils through field tests, limit equilibrium analysis, or finite element numerical simulation and found that geosynthetics reinforcement significantly improved the structural stability and reduced the deformation of soil [5][6][7][8][9][10][11]. ...
This paper presents an analysis on a geogrid-reinforced embankment with clay-cover by model tests under static and cyclic loading. The deformation and failure surface inside the embankment were obtained by particle image velocimetry (PIV). The test results showed that geogrids effectively improved the ultimate bearing capacity and reduced the vertical settlement and lateral displacement of reinforced embankment. The reinforcement effect increased with the increase in geogrid length, and the ultimate bearing capacity of the embankment reinforced with the longest geogrid was 51.9 kPa, which was 79% higher than that of unreinforced embankment. The wrapped clay formed an effective lateral constraint on the outward movement of the slope soil under pressure. When the reinforced embankment was damaged, the internal displacement significantly reduced, and the sliding surface in the middle of the embankment pointing to the foot of slope began to move into the embankment in an arc shape. In the cyclic loading test, the stress concentration effect inside embankment reduced by geogrid reinforcement. During each cycle, the earth pressure varied with a stable half-sine wave. The conclusions drawn from this study can provide an important fundamental data for the construction in geotechnical and road engineering.
... Recently, thanks to the development of experimental models and numerical simulation tools, many authors have studied and clarified the interaction between geosynthetics and soil [3][4][5]. However, there are not many studies evaluating the apparent cohesion of reinforced soils. ...
In this article, the authors use Plaxis 2D software to simulate triaxial testing that shows the behavior of the geogrid reinforced soil structures under the effect of loads. Based on the Mohr - Rankine limit equilibrium conditions, the apparent cohesion generated by the geogrid layers is determined. The article has established 62 different numerical simulation problems on input parameters such as the internal friction angle of soil, the distance of layers, and the strength of geogrid. From numerical analysis results, combined with the nonlinear regression method, the authors have built a formula to determine the apparent cohesion of the reinforced soil structures.
... Results show that the GRS abutment with close spacing has an excellent service performance and a high load-carrying capacity to meet the design requirements. However, the input parameters for constitutive models in the numerical analysis are based on a large number of laboratory soil tests, which may cause the uncertainty of the numerical results [20]. Raja et al. [21] proposed a novel hybrid artificial intelligence (AI)-based model to predict the load-settlement behavior of the GRS abutment. ...
This study conducted plane-strain scaled model tests to investigate the deformation characteristics of geosynthetic reinforced soil (GRS) abutments subjected to vertical loads. Setback distance, i.e., the distance between the back of the abutment facing and the front of the loading plate, was chosen as the investigated influencing factor since it is one of the most frequently used variables by engineers for the design of GRS abutments. This study analyzed the settlements at the top of the abutment, the lateral displacements of the abutment facing, and the volumetric deformation of the abutment under the applied vertical loads. Test results showed that increasing the setback distance could effectively reduce the deformations of the GRS abutment. There existed an optimum setback distance and further increasing the setback distance beyond this optimum value did not have a significant effect on reducing the abutment deformations. The vertical, lateral, and total volumetric deformations of the GRS abutment showed an approximately linear increase with the increase of the applied vertical loads. The lateral volumetric deformations of the GRS abutment were larger than its vertical volumetric deformations and therefore the total volumetric strains of the GRS abutment were not zero based on the test results. However, the theory of zero volume change may still be suitable for the deformation calculation of the GRS abutment since the values of the volumetric strains were minimal. The measured maximum lateral facing displacements were compared with the calculated values using the US Federal Highway Administration (FHWA) method, which assumes zero volume change of the GRS abutment under vertical loads. Comparison results indicated that the FHWA method overestimated the maximum lateral facing displacements of the GRS abutment under vertical loads. An improved method was proposed in this study to calculate the maximum lateral facing displacements under vertical loads based on the theory of zero volume change and a revised distribution of the settlements at the top of the GRS abutment. Results showed that the improved method could better predict the maximum lateral facing displacements as compared to the FHWA method.
... The subgrade strength was evaluated by conducting CBR test on the sample, and more increment in the CBR value was found when reinforced with geosynthetics as compared to Tenax 3-D reinforcement [10]. The comparative laboratory investigation was performed on square footing placed over foundation bed reinforced with different geotextile materials and found that geocell reinforcement was more effective in enhancement of bearing capacity due to 3-D confinement behavior [11,12]. When medium sand bed was stabilized with tire shreds, there was a twofold increase in bearing capacity along with a 34% decrease in settlement value [13]. ...
Due to their disposal issues, the waste materials are a major worry for the globe. The thermal power facilities generate a significant quantity of pond ash, which provides a disposal challenge and is not ecologically friendly. To mitigate these issues, these waste materials can be used as the replacement of construction material for the cost optimization. The present work is basically focused to analyze the effect of sand replacement on load carrying capacity of pond ash using plate load test. Furthermore, the comparison results were presented, for both jute geotextile and geogrid corresponding to various embedment depth below base of footing. The study found that there was maximum enhancement in density of deposit corresponding to 15% sand replacement and this proportion can be utilized in the preparation of foundation bed. The general shear failure was observed during failure in experimental investigation. Additionally, it was examined that adding multiple layers of jute geotextile and geogrid enhanced the bearing capacity of foundation bed. The ideal depth to embed a single layer of jute geotextile and geogrid underneath the footing was found to be 0.3B and 0.5B, respectively.
... They reported that a geogrid-reinforced foundation bed improves the bearing capacity and reduces the settlement. Since after several researchers have experimentally investigated the potential benefits of using geogrids as tensile reinforcement to enhance the bearing pressure of homogeneous sand [7][8][9][10][11][12][13][14]. The optimum numbers, width, length, spacing, and position of the geogrid layer layers have been investigated by these researchers. ...
Laboratory model tests have been performed to investigate the bearing pressure of a circular foundation lying on geogrid-reinforced dense sand over weak clay. The undrained shear strength of clay varied as 7, 14, and 28 kPa. The relative density and depth of the sand layer were kept constant during the experiments. Experiments were performed on homogeneous soil (clay, sand), layered soil (clay and sand), and layered soil with geogrid reinforcement. The bearing pressure ratio (BPR) or improvement factors (the ratio of the bearing pressure of reinforced soil to the bearing pressure of homogeneous clay at the same level of undrained shear strength of the soil) have been used to evaluate the model tests' performance. Based on experimental results, it has been found that the bearing pressure of foundation beds increased when sand was placed over the clay bed. Also, bearing pressure improvements have been found when geogrid reinforcement was used at the junction between clay and sand beds. The highest improvement factor for geogrid-reinforced layered soil was observed to be 3.79 for very soft clay (Cu = 7 kPa). Artificial neural networks (ANNs) have been developed for predicting the bearing pressure of foundation beds using the results of laboratory model tests. To minimize errors in the models, the number of neurons and the number of hidden layers were changed. From the developed model, it has been found that artificial neural networks can predict the bearing pressure of reinforced foundation beds very accurately. The maximum benefit has been found (R2 = 0.9940, MAE = 3.42, RMSE = 4.37) for models having three hidden layers with 20 neurons in each hidden layer.
... Geotextiles manifest unique advantages in reinforcing granular materials (Fattah et al., 2020), especially coral sands with strong roughness and occlusions (Balakrishnan and Viswanadham, 2019;Roy and Deb, 2020;Xu et al., 2019). Goodarzi and Shahnazari (2019) investigated the mechanical properties of geotextile-reinforced coral sands from the northwest coast of Hormoz Island in the Persian Gulf under drainage conditions. ...
Porous coral sands formed by the remains of marine organisms are important foundation-filling materials for artificial island construction and other marine geotechnical projects. A typical situation is that the significantly reduced bearing capacity of a rigid footing adjacent to coral sand slopes threatens the safety and stability of the upper structures. In this study, a series of model-scale tests were conducted to investigate the bearing capacity and deformation behavior of a rigid strip footing resting on the top of coral sand slopes with consideration of the effects of edge distance, slope height, slope angle, number of geogrid layers, burial depth and spacing of the geogrid layer. The measured deformation field based on particle image velocimetry (PIV) technology indicates that the unreinforced coral sand slope is dominated by unilateral sliding patterns, and its bearing area is significantly smaller than that of the geogrid reinforced coral sand slope (GRCSS). The bearing capacity in unreinforced coral sand slopes increases with the increasing edge distance, and the decreasing slope height and angle. Although the geogrid reinforcement significantly improves the bearing capacity, it is also affected by the number of layers, burial depth and spacing between reinforcement layers. Besides, the reduction coefficient of bearing capacity (RCBC), the bearing capacity factor (Nγq) and the normalized bearing capacity (Nγq/NγqR) were further calculated and discussed based on the test results and classical bearing capacity theory.
... The use of reinforced soil (RS) walls, treated as a new, more economical proposition compared to conventional retaining walls, has increased significantly across the world during the last few decades. In recent periods of time, a large number of such structures has been built because of their numerous advantages, including reliability, aesthetics, cost effectiveness, simplicity of construction, tolerance of differential settlements, and good seismic performance [1][2][3][4][5][6][7][8][9][10][11][12][13]. ...
This paper presents the results of an experimental investigation of a vertical reinforced soil (RS) wall. The structure was built on a laboratory scale. Horizontal displacements on the surface of the model wall were monitored at the end of construction and during surcharge application (as post-construction displacements). The experimental results were compared with their theoretical predictions. The accuracy of the selected analytical approach was examined to predict deformations of the RS structure under external loading. It was shown that the proposed original and relatively simple analytical method for estimating structural deformation can be successfully used in practice (the average difference between the recorded and calculated values of deformation did not exceed 25%). From a scientific point of view, an important element of this work was the analysis of the effect of friction between the backfill and the side walls of the test box on the measured displacements. For the investigated case, it was shown that the impact of this element caused a reduction in the value of external loading of more than 60%. The final results may be particularly useful in the design process of structures used in transportation engineering (bridge abutments), where deformation limit values cannot be exceeded.
In this paper, plate loading tests were conducted to investigate the load and deformation behaviors of the geogrid-reinforced sand foundation under circular footing with a diameter of 0.4 m. The parameters examined include the reinforcement tensile stiffness, the number of reinforcement layers, and the spacing between reinforcement layers. The vertical stresses in the soil, surface deformations and strains in geogrids were monitored during loading. Test results show that the efficiency of geogrids in improving soil's bearing capacity is closely related to footing settlement. The larger the settlement, the better the reinforcing effect as s/D > 3%, where s and D is the settlement and diameter of circular footing, respectively. The stiffness, spacing and number of reinforcements significantly influence the stress distribution effect of geogrid-reinforced zone. The effective influencing depth and diameter of the stress distribution effect are approximately 3D and 1.4D, respectively. Generally, the maximum tensile strain in the geogrids occurs around the footing center, while the maximum compressive strain is located at approximately 1D from the center. The maximum tensile strain is greater affected by the vertical spacing, whereas the number of reinforcement layers has a significant effect on the maximum compressive strain.
The effect of geotextile inclusion on the shear modulus and damping ratio of sands is evaluated in a wide range of shear strain amplitudes, from very small to fairly large, using the results of several resonant column and hollow cylinder torsional shear tests. The resonant column test results are utilized to characterize the reinforced soil behavior at the range of small to medium strains whereas the hollow cylinder torsional shear test results are exploited to assess the medium to large strain dynamic properties. The results demonstrate that the inclusion of geotextile sheets in the soil medium would increase both its shear stiffness and damping ratio in the whole range of shear strain amplitudes, thus rendering a perfect composite to resist dynamic forces applied on geo-structures in earthquake prone areas. Empirical equations are proposed to estimate the small strain and strain-dependent shear modulus and damping ratio of geotextile-reinforced sands. The effect of scaling is also accounted for by a simple analysis so that the results obtained in the current study in the element scale could be extended to the prototype scale in the field. Finally, the accuracy of the proposed scaling approach is verified against a finite element model of a geotextile-reinforced embankment.
Five centrifuge models of geosynthetic reinforced soil (GRS) abutments with segmental block facing were loaded in acceleration field under plane strain condition. Influences factors including reinforcement tensile strength, setback and bearing area width were considered and analysed. Results show that the abutment with stronger reinforcement remained stable under the maximum loading capacity. However, abutments with weaker reinforcement showed excessive vertical strain, local deformation or even collapse. The ultimate bearing capacity increased with the lengthening of setback while decreased due to a larger bearing area. The rupture of reinforcements was observed and considered as the cause of the failures. Comparing with the measured ultimate bearing capacity, the values calculated by the semi-empirical formula of design guideline were significantly conservative. The failure surface of failed abutment developed from rear edge of the bearing area to the middle height of the abutment at an angle of nearly 45°+φ/2. The setback and the bearing area width affected the form and position of the failure surface. The difference between the potential failure surface predicted by available methods and the measured failure surfaces has been discussed, and suggestions for the design and ultimate bearing capacity prediction of GRS abutments with segmental block facing were provided.
In this study, the ultimate bearing capacity of shallow strip footings resting on a geosynthetic-reinforced soil mass subjected to inclined and eccentric combined loading is rigorously examined through the well-established method of lower bound limit analysis (LA) in conjunction with finite element (FE) and second-order cone programming (SOCP). Lower bound limit analysis formulation is modified to consider the ultimate tensile force of the geosynthetic layer in the soil mass so as to account for both pullout (sliding) and rupture (structural) modes of reinforcement failure. The effects of several parameters, including the embedment depth (u) and the ultimate tensile force (T u ) of the geosynthetic layer along with load inclination angle (α) and load eccentricity (e), on the bearing capacity ratio (BCR) and failure envelopes of the overlying shallow foundation are examined and discussed. The results generally show a marked increase in the ultimate bearing capacity of the surface footing against combined loading with the inclusion of a single geosynthetic layer. Results also reveal that a second intermediate reinforcement might be required to bear a dual performance against both vertical concentric and combined loading so as to more effectively support the footing.
Road construction in karst areas is a challenging task. Combining the advantages of geosynthetics and fiber Bragg grating (FBG), this paper creatively presents a new type of FBG-3D printed geogrid, which allows reinforcement and accurate deformation monitoring. A series of model tests were carried out to investigate the mechanical and deformation characteristics of the subgrade with underlying karst cave reinforced by FBG-3D printed geogrid. The experimental results indicated that the fully coordinated deformation between FBG sensor and geogrid was successfully achieved by 3D printing technology, and the relationship between fiber wavelength and strain was obtained. The existence of cave had an adverse effect on the subgrade, but the FBG-3D printed geogrids effectively improved the bearing capacity and footing settlement, and the reinforcement effect increased with the decrease of geogrid spacing. In the cyclic loading experiments, the earth pressure inside the subgrade reinforced by geogrid changed as a half-sine wave in each cycle. The FBG sensors accurately measured the strain change inside the subgrade, and the data showed that the deformation of measuring point above the cave model was the largest. The research conclusions provide important basic data for the construction and monitoring of highway and geotechnical engineering projects.
The main cities in West Africa have been characterized by the development of infrastructure in past decade. This paper examined the performance of the soil and of pavement in Benin (West Africa). In this research, four objectives have been adopted in-depth on the performance characteristics of West African soil and aim to (i) accessing characteristics of soil types in the region; (ii) assessing the performance of these soils with 3% of lime, with the combination of 3% lime and 3% cement; (iii) using geogrid to evaluate the performance of pavement on clayey soil; (iv) proposing a new pavement model strategy considering economic aspects of construction. The methods used to examine these objectives are experimental tests according to standard French test. Design of flexible pavement is largely based on empirical methods according to the transport research laboratory (TRL) Note 31 with WinJulea software and compared with a designed and evaluated pavement structure adopting the center experimental of building and public works (CEBTP) method. In addition, the research quantified the percentage of biaxial geogrid impacting the performance of pavement in a diminishing perspective. Flexible pavements (with and without geogrids) were built and subjected to 127.49 kN load applications. This paper firstly reveals the unstable and stable areas in southern Benin (West Africa) with the presence of clay soil, and secondly reveals that the use of 3% lime and the combination of 3% lime and 3% cement are limited in subgrade. In addition, the TRL Note 31 with WinJulea software is more economical while the one of CEBTP highly performs. More so, the paper confirms that the use of biaxial geogrid reinforcement in pavement structures highly reduces the construction cost. As conclusion, firstly, the pavement made from the recycled asphalt pavement materials with biaxial geogrid in subgrade is the best in the clayey area.
In this study, a series of cyclic triaxial tests were conducted to study the accumulated strain of coarse-grained soil reinforced with geogrids, and the effect of the number of geogrid layers, confining pressure and cyclic stress amplitude was investigated in detail. The test results show that the final accumulated axial strain of the soils reinforced with geogrids is less than that without reinforcement, and less accumulated axial strain is generated for the specimens with more geogrid layers under identical cyclic loading. The results also show that a higher confining pressure or a lower cyclic stress amplitude yields less accumulated axial strain for the reinforced soils. Furthermore, the plastic shakedown limits are determined by the criterion proposed by Chen et al. It indicates that the plastic shakedown limit increases significantly when one layer of geogrid is incorporated into the specimen and then tends to level off with a continuous increase in the number of geogrid layers. Moreover, a higher confining pressure yields a higher plastic shakedown limit for the soils reinforced with geogrid. The results demonstrated that the use of geogrid can be an effective method to reduce the accumulated deformation of subgrade filling materials under high-cycle traffic loading.
Bump problems at the bridge approach cause riding discomfort and result in safety issue to the road users. The Geosynthetic Reinforced Soil-Integrated Bridge System (GRS-IBS) is a recent bridge approach construction system that connects the bridge deck and roadways without joints and bearings, thus capable to eliminate the bump problems. This system is gaining popularity for low to medium bridge construction due to its relatively faster, lower cost, and simple construction process. The GRS abutment is a composite geotechnical structure with internally supported reinforcement. A close spacing reinforcement of 0.2–0.3 meter in between the compacted granular backfill of high shear resistance has improved the bearing capacity of the GRS abutment, hence capable to support the bridge loads directly. In this paper, a thematic literature review on the bump problems and GRS-IBS system is presented. Summaries of previous studies are tabulated and discussed, inclusive of case studies, physical models, numerical models, and key factors affecting the performance of GRS-IBS. Limitations posed to this system are also provided at the end of this article. The review and summary of this paper are expected to provide meaningful information to the readers.
Geofoam, one of the geosynthetic types, is a foam material used in geotechnical applications. Geofoam synthetic material, EPS (expanded polystyren), is used in road constructions, retaining walls, and superstructures that require heat and sound insulation (building, school, etc.). In the study, the bearing capacity, deformation properties, and economic aspects obtained by the use of EPS material in road constructions were investigated. In this respect, it has been observed that EPS is more economical in the long run than other ground fills (soil, rock…). Since EPS is applied vertically, it reduces the amount of material and shortens the project implementation time because it is practical. Since the material is light, machines are not needed during application. In terms of bearing capacity, it carried the given loads when used as a road fill. The strength-deformation properties of EPS and soil fillings were compared using the finite element analysis method. The maximum pressure to be applied to the material is determined as the pressure exerted on the surface by the wheel of the truck with the heaviest tonnage. When EPS and ground fill are compared with finite element analysis in terms of strength-deformation, it has been observed that more deformation occurs in EPS fill.
Geogrid has been extensively used in engineering practice as a horizontal reinforcing material to improve the performance of foundations, embankments, and road base systems. This paper presented the results of laboratory static load tests on transparent soil foundations reinforced with biaxial polylactic acid geogrid and studied the reinforcement mechanism and foundation failure mode of the reinforced foundation. The different load settlement behaviour between reinforced foundations with different reinforcement layer numbers was studied by varying the number of geogrid layers. The deformation of reinforcements and foundation soil was recorded with an industrial camera. The strain of the reinforcements was monitored by Fiber Bragg Grating (FBG) sensors. In addition, a two-dimensional discrete element model was established based on the model tests to analyse the load transfer behaviour and deformation law of the reinforced foundation. The results indicated that geogrid can effectively improve the bearing capacity of the foundation. As the number of reinforcement layers increases, the improving effect is more significant. The reinforced soil can provide a stronger upward resistance than unreinforced soil by activating the tensile force of the geogrid. The simulation results present the load transfer behaviour and reinforcement mechanism of geogrid. With the increase of reinforcement layers, the position of the sliding surface moves downward, and the area of the sliding surface increases. Geogrid can limit soil displacement and delay the development of the sliding surface.
This paper presents the results of centrifuge model tests to investigate the deformation behavior of unreinforced and reinforced transparent soil foundations under strip loading. Digital image analysis technique was employed to obtain the soil displacement field and strain distribution of reinforcements. Two-dimensional numerical models were developed and verified using the test results. The soil was modeled as a linearly-elastic perfectly-plastic material with Mohr-Coulomb failure criterion. The reinforcement was characterized using a linearly-elastic model with considering rupture behavior. Moreover, a parametric study was conducted to investigate the load-settlement response of foundations, distribution of reinforcement tension and failure sequence of reinforcements. The experimental and numerical studies show that the results obtained from the numerical simulations are in good agreement with the results of the centrifuge model tests. The two-dimensional finite difference model developed using the user-defined functions coded into the program FLAC can better simulate the progressive failure of the reinforcement layers in the tests. The failure sequence of reinforcement layers is not affected by the modulus and internal friction angle of soils and the reinforcement length, but is closely related to the combining effect of spacing and number of reinforcement layers and the combining effect of reinforcement stiffness and strength.
This paper presents interaction experiments with transparent soil to investigate the load transfer at the interface of different geosynthetic reinforcements. Microscopic interaction performance was evaluated in terms of mobilised tensile loads and interfacial shear stresses resulting from the relative movement between geosynthetic and soil. The effects of geogrid aperture size, tensile stiffness, geogrid type and reinforcement configurations on the load transfer were analysed. It was found that with increasing soil deformation, the contribution of friction to the total load transfer decreased and the transverse ribs were increasingly activated. The interfacial shear stresses were reduced as the ratio of geogrid aperture to mean particle size increased, resulting in lower geogrid loads. Higher geogrids loads were mobilised with increasing tensile stiffness of the reinforcement, but lower displacements of geogrid and adjacent soil occurred. Consistent results were found for woven PET and laid PP geogrids. The most effective load transfer was obtained for the aperture configuration with two closely spaced transverse members at each rib, as the soil particles were additionally confined. When the geogrid was attached to a nonwoven geotextile, the separation function was enabled, but the reinforcement performance of the geocomposite was lower due to reduced particle-aperture interaction.
This paper is to investigate the influence of reinforcement material types on the bearing and deformation characteristics of reinforced earth retaining wall. A series of large-scale static and dynamic model tests were carried out. Some characteristic parameters of the geogrid-and geocell-reinforced earth retaining walls were analyzed, such as additional vertical earth pressure, vertical settlement, lateral deformation, and dynamic acceleration response. The test results show that the ultimate bearing capacity of the geogrid-reinforced earth retaining wall was 2.5 times as much as that of geocell-reinforced earth retaining wall. And the maximum lateral displacement of the geogrid-reinforced earth retaining wall was only 0.1 of the geocell-reinforced earth retaining wall. Compared with the geocell-reinforced earth retaining wall, the geogrid-reinforced earth retaining wall has higher bearing capacity and resistance to deformation. Compared with geocell, geogrid has a stronger homogenization effect on the vertical pressure inside the reinforced earth retaining wall. However, under the same load conditions, the peak acceleration of soil within the geocell-reinforced earth retaining wall is smaller than that of the geogrid-reinforced earth retaining wall. Additionally, based on the assumption of null volumetric strain, a new Adams maximum lateral displacement correction model was proposed. The error between the predicted value and the measured value of the maximum lateral displacement of the geogrid-reinforced earth retaining wall is within 10%, which shows that the model has a good prediction.
Geogrids are extensively used to improve the bearing capacity of low strength soil and reduce the settlement of soft soil foundations. This study aims to compare the bearing capacity and deformation characteristics of geogrid reinforced foundation with different types of geogrids (uniaxial, biaxial, triaxial) and different reinforcement layers (N = 1, 2, 3) in reduced-scale transparent soil model tests. The images of the foundation model are captured by the laser transmitter and digital camera. These images are further analyzed to study the foundation deformation of different cases by digital image processing technique. The results show that triaxial geogrid reinforced foundation has a better bearing capacity than the uniaxial geogrid and biaxial geogrid reinforced foundation. In the process of foundation settlement, the slip crack surface and ground heave gradually develop with the bottom-up diffusion of horizontal and vertical displacements of the soil. Local shear failure first occurred in the bottom of the foundation, and then transformed into general shear failure. These results visualize and quantify the soil displacement transfer and spreading behavior in geogrid reinforced foundations. This paper illustrates the effects that geogrid reinforcing at a microscopic scale under strip footing loads.
This paper presents an experimental study on reduced-scale model tests of geosynthetic reinforced soil (GRS) bridge abutments with modular block facing, full-height panel facing, and geosynthetic wrapped facing to investigate the influence of facing conditions on the load bearing behavior. The GRS abutment models were constructed using sand backfill and geogrid reinforcement. Test results indicate that footing settlements and facing displacements under the same applied vertical stress generally increase from full-height panel facing abutment, to modular block facing abutment, to geosynthetic wrapped facing abutment. Measured incremental vertical and lateral soil stresses for the two GRS abutments with flexible facing are generally similar, while the GRS abutment with rigid facing has larger stresses. For the GRS abutments with flexible facing, maximum reinforcement tensile strain in each layer typically occurs under the footing for the upper reinforcement layers and near the facing connections for the lower layers. For the full-height panel facing abutment, maximum reinforcement tensile strains generally occur near the facing connections.
This paper presents a case study of the first geosynthetic reinforced soil-integrated bridge system (GRS-IBS) with with full-height rigid facings in China. Open graded gravel and biaxial geogrid were used for the GRS-IBS. Steel frame and 3D vegetation net were used as temporary facing support during construction of the GRS abutments. Full-height rigid facings were cast in place on strip foundations. Field monitoring results of vertical stress distribution for different construction stages and loading conditions are presented and discussed. For both bridge dead load and truck loads, measured incremental vertical stresses under the beam seat increase significantly with increasing elevation, especially for higher applied vertical stress. The calculated incremental vertical soil stresses using the Boussinesq solution are in reasonable agreement with the measured values, while the 2:1 stress distribution method overestimates the incremental stresses in the lower section of the abutment. The transferred vertical stresses from bridge load application for the GRS abutment with full-height rigid facing are larger than those for the GRS abutment with modular block facing near the top of the abutment, but are smaller near the bottom.
Performing tests on geosynthetic-reinforced soils under pullout conditions gives a comprehensive understanding of soil-geosynthetic interaction. However, they may be expensive and time-consuming. Therefore, the development of theoretical solutions may be beneficial to recognize characteristics of geosynthetic-reinforced soils under pullout conditions. This paper proposes an analytical solution for the determination of pullout force-deformation variation of planar geosynthetics reinforcing unsaturated cohesive-frictional soils. The solution predictions were validated with experimental results, demonstrating the capability of the presented solution. The solution can extend limited results obtained from experiments to a wider range of conditions. It has been demonstrated that under 20 kPa overburden stress, with decreasing the soil suction from 1153 to 312 kPa, corresponding to increasing the moisture content from 16% to 20%, the peak pullout force decreases by about 28%. The results also illustrate that by increasing the value of matric suction, the amount of U* (relative soil-reinforcement displacement corresponding to the total mobilization of friction) decreases.
In this paper, upper bound limit analysis that includes a horizontal pseudostatic seismic force is used for the first time to obtain the limit load on strip footings seated on cohesive-frictional soils reinforced with a single geosynthetic layer. Reinforcement tensile rupture and sliding failure modes for the geosynthetic layer are included in the analyses. Results of analyses are presented as optimum reinforcement depths and a bearing capacity equation with a single term and different bearing capacity factors for tensile rupture and sliding failure modes. The bearing capacity factors are presented in tables and capture the combined influence of the reinforcement strength, soil frictional strength and cohesion, soil unit weight, footing geometry, uniform surcharge, and magnitude of horizontal ground acceleration.
To explore the reinforcement effects of different reinforcement methods, kraft paper was used as reinforcement material, and shear tests were carried out in sand to study the reinforcement effects of kraft paper perpendicular and parallel to the shear plane. The test results show that the two reinforcement methods can effectively improve the strength of sand and the orthogonal reinforcement form is more superior. The existence of reinforced materials greatly improves the cohesion of sand, but does not significantly improve the internal friction angle. The width of reinforcement material has little effect on the reinforcement effect and shows different variation laws under different reinforcement forms.
This paper presents two-dimensional (2D) and three-dimensional (3D) numerical simulations of a half-scale geosynthetic reinforced soil (GRS) bridge abutment during construction and bridge load application. The backfill soil was characterized using a nonlinear elastoplastic model that incorporates a hyperbolic stress–strain relationship and the Mohr–Coulomb failure criterion. Geogrid reinforcements were characterized using linearly elastic elements with orthotropic behavior. Various interfaces were included to simulate the interaction between the abutment components. Results from the 2D and 3D simulations were compared with physical model test measurements from the longitudinal and transverse sections of a GRS bridge abutment. Facing displacements and bridge seat settlements for the 2D and 3D simulations agree well with measured values, with the 2D-simulated values larger than the 3D-simulated values due to boundary condition effects. Results from the 3D simulation are in reasonable agreement with measurements from the longitudinal and transverse sections. The 2D simulation can also reasonably capture the static response of GRS bridge abutments and is generally more conservative than the 3D simulation.
Application of Geosynthetic to resolve several geotechnical engineering problems is widely accepted and effective methods. It improved the foundation’s bearing ability as well as minimizes the settlements associate to footings resting on weak soils. Their use is not only restricted to footings in fact they are widely used in improving the subgrade performance of the pavement sand for slope stabilizations. Over the past few decades numerous researchers have contributed their valuable results based on laboratory tests or numerical investigations. The present study aims to provide a detailed literature survey of research work associated with soil reinforcements together under a common hood which can help the upcoming researchers to understand the work done in this field simply and effectively. It also aims to highlight the effect of depth of geosynthetics, their respective width, relative density of sand or other geo-parameters and layers’ number provided with geosynthetic affect the bearing capability and settlement behavior of reinforced and unreinforced soil structures.
Peat soil is a soft material from the group of organic soils. This soil has different behavioral characteristics than other nonorganic soils. One of its weaknesses is insufficient shear strength. Therefore, any construction and loading on it require special measures such as reinforcement. The present study aims to experimentally investigate the shear behavior of peat soil reinforced with geotextiles. In this research, first undisturbed samples of the Urmia peat soil were collected from in situ road construction site of Urmia to Tabriz. After determining its initial physical characteristics, direct shear tests under vertical stresses of 10, 20, and 30 kPa with changing strain rate of 0.9 mm/min and 0.1 mm/min were conducted on two types of peat soils with average organic material content of 33% and 72%, respectively. In the second part, direct shear test was performed between peat samples and two types of geotextiles with tensile strengths of 30 and 6 kN/m. The results showed that the percentage of organic materials in peat plays a significant role in its friction angle (φ), and the peat with higher rate of organic materials has higher frictional behavior and less cohesion (c). Also, the application of geotextile, depending on its tensile strength and the amount of organic materials in the peats, has different results in increasing the peat friction angle. The test results show with higher amount of organic materials in peat and the greater tensile strength of the geotextile; frictional resistance between peat and geotextile may be greater than in peat alone.
The advent of industrialization and unrestrained urbanization created a demand for the construction of heavy engineering infrastructures which caused extensive environmental deterioration. Also, the construction industry generates huge waste in the form of demolished material and recycled material. Therefore, the need of the hour is to explore all alternative approaches and materials which are durable, sustainable, and transcendent in comparison with the conventional building materials being used for construction. In view of the above, recycling and using the construction and demolition wastes have emerged as a suitable substitute for civil engineering applications as it utilizes the otherwise leftover waste product, saves natural resources, and reduces our environmental footprint. The geotechnical properties of the construction and demolition materials have shown low variability when compared with the guidelines of various agencies for their utilization as backfill materials in structures that are reinforced with geosynthetic materials. The adherence factor (ratio between the pull-out strength of the interface and the shear strength of the backfill) when calculated for geogrid construction and interfaces of the demolition materials were almost in a similar limit w.r.t the soil-geogrid interface values attained by few other researchers. Therefore, given the above, this study aims to present a detailed overview on the performance and evaluation of construction and demolition materials in mechanically stabilized earth retaining structures (using geosynthetic as a reinforcing layer), while highlighting its application as backfill material for retaining walls and building and construction material for the embankment creation.
This paper presents the numerical results of the performance of the Geosynthetic Reinforced Soil Integrated Bridge System (GRS-IBS) due to differential settlement underneath the reinforced soil foundation (RSF), underneath the reinforced zone including the RSF, and underneath the retained soil. The performance was evaluated in terms of reinforcement strain, lateral facing deformation, bump at the approach roadway-bridge slab intersection, and lateral facing pressure. Four different differential settlement values of 50, 100, 150, and 200 mm were selected for this study under three different service loading conditions corresponding to bridge spans of 24.4, 30.5, and 36.6 m. Simulations were conducted using the two-dimensional (2D) PLAXIS 2016 finite element (FE) program. The hardening soil model was used to simulate the backfill material behavior. The interface between the backfill material and the reinforcement was simulated using the Mohr-Coulomb model. The reinforcement and facing block were simulated using the linear elastic model. The results of FE analyses indicate that the differential settlement under the RSF has a high impact on both the strain distribution along the reinforcement and the lateral facing displacement.
Despite great promise of excellent performance characteristics of geosynthetic reinforced soil (GRS) bridge abutments under static loads, their response under earthquake loading remains a concern. In order to advance and implement this new technology, especially in seismically active regions, this study was undertaken to examine the performance of GRS bridge abutments under seismic loads in a rational and critical manner and to present rational guidelines for design and construction of earthquake-resistant GRS bridge abutments. This paper reports a field-scale shake table test that was performed to provide relevant data for validate an analytical procedure for GRS abutments. The abutment model withstood vertical and horizontal loads placed on it during ground accelerations of 0.15 g at 1.5 Hz and did not experience structural failure or significant movement. The model sufficiently withstood the bridge loads while being subjected to ground accelerations up to 1.0 g at 3 Hz. This paper describes the instrumented field-scale GRS bridge abutment shake table test and reports the test results.
The bridge across the Pavlovski potok stream in the village of Žerovinci in northeast Slovenia is a part of the investment into the modernisation of the Pragersko–Hodoš railway line, one of the biggest investments in the infrastructure in Slovenia at the moment. Its design was accompanied by very short deadlines and a deep layer of soft foundation soil. For this reason the reinforced concrete abutments of a nearby railway bridge were founded on 24 m deep piled foundations. Short deadlines and a limited budget forced the authors of this paper to find an alternative solution. Deep piled foundations were replaced by shallow foundations made of compacted fill material reinforced with geosynthetics. The bridge was completed by the end of 2014. From the results of previous laboratory tests that were obtained within the scope of the EU co-funded research project “Research voucher”, the basic characteristics of the building materials for the geosynthetic reinforced soil (GRS) bridge abutments, as well as the deformation properties of the typical reinforced soil were obtained. These data were used for the design of the abutments. The staged construction procedure of full height rigid (FHR) facings for the GRS retaining walls (RW) was used for the construction of this GRS integrated bridge. Partial pre-stressing of geogrids and consequently the increased stiffness of the reinforced soil was achieved by following the staged construction procedure. The bridge system consisted of a cast-in-situ RC slab, which was placed on top of the GRS immediately behind the FHR facings, i.e. the bridge was constructed as a simply-supported slab supported by a pair of GRS abutments, without the use of bearings. Thus the described bridge across the Pavlovski potok combines two approaches for GRS integrated bridge design, one of which has been used in Japan (Tatsuoka et al., 2009), with full structural integration of the deck onto the pair of FHR facings, other being proposed by the FHWA (Adams et al., 2010), without full integration of the deck onto the GRS RWs. A system for the monitoring of structure performance was established in order to ensure optimization of this kind of structure. Data for this GRS integrated bridge, which were obtained during the construction works were compared to similar data obtained from the construction of a nearby railway bridge with reinforced concrete abutments. The comparison provides a good basis for future decisions when choosing the type of bridge abutments.
Diaphragm-type pressure cells are often used in geotechnical model tests and in-situ tests. The soil pressures are obtained through the measurement of the diaphragm deflection. With a gauge inserted into the soil or sand, the stiffnesses of the cells and the geo-medium are different. The soil arching in the soil or sand above the cells caused by the differential deformation will reduce the pressure on the diaphragm. In addition, different stress histories in the model tests result in different levels of influence. In the piled embankment multiple trapdoors model tests, the cells on the pile (fixed beams) experience a loading process, while the cells in the soil (movable beams) experience an unloading process. One loading calibration test and four unloading calibration tests are carried out on the same sand under the same relative density as in the model tests. The calibration results show that the stress-strain loading curves are almost linear and the unloading curves are quite similar to exponential ones. The calibration coefficients are obtained and then used to deal with the measurements. During the sand filling procedure, the average pressures obtained using the calibration coefficients coincide well with the self-weight of the embankments. During the settling (trapdoor movement) procedure, the pressures of the cells on the pile and in the soil are calculated using loading coefficients and unloading coefficients respectively. The results show that the soil pressure curves coincide well with those in the real model tests. © 2016, Editorial Office of Chinese Journal of Geotechnical Engineering. All right reserved.
A new method for the internal design of reinforced soil walls is developed based on working stresses conditions. This method is a simplification of Ehrlich and Mitchell's 1994 design procedure. The maximum reinforcement loads, Tmax, calculated using the new proposed method were compared with those calculated by the original method. The comparisons were performed considering a wide range of wall heights, reinforcement stiffnesses, compaction efforts and backfill soil parameters. The results show good agreement between the original and simplified methods (less than 5% variation). Moreover, the new simplified method was extended to include the effect of facing inclination, which was not available in the original procedure. Data from physical and numerical model studies were used to verify the predictability of the simplified method for walls with different heights, facing inclinations, reinforcement stiffnesses and backfill soil parameters. The results indicated that the simplified method is also capable of properly capturing Tmax when the face of the wall is inclined.
A trapdoor system has frequently been used to study soil arching and its development in recent years. The load transfer in the fill of piled embankments is very similar to a trapdoor system with multiple trapdoors. There are multiple arching models described in different standards and guidelines for piled embankments that can be subdivided into three arching-model families. To study the soil-arching type and its development, a series of model tests with sand fills were carried out in a two-dimensional (2D) multi-trapdoor test setup. The tests considered four factors - the fill height, trapdoor width, pile width, and grain size of the sand - with four values for each factor. Triangular slip surfaces were found at very small deformations using the particle image velocimetry (PIV) technique. These surfaces evolved in ways that could be related to the three types of stress-distribution ratio curves, with development patterns similar to the arching families of piled embankments: (1) the rigid-model family, (2) the equal-settlement-plane-model family, and (3) the limit-equilibrium-model family. The limit-equilibrium-model family occurred in tests with narrow trapdoor widths.
A geosynthetic-reinforced soil (GRS) system was constructed to support the shallow footings of a two-span bridge and the approaching roadway structures. Construction of this system, the Founders/Meadows bridge abutments, was completed in 1999 near Denver, Colorado, USA. This unique system was selected with the objectives of alleviating the "bump at the bridge" problem often noticed when using traditional deep foundations, allowing for a small construction working area, and facilitating construction in stages. The primary focus of the paper is to evaluate the deformation response of this structure under service loads based on displacement data collected through surveying, inclinometer, strain gages, and digital road profiler. The overall short- and long-term performance of the Founders/Meadows structure was excellent, suggesting that GRS walls are a viable alternative to support both bridge and approaching roadway structures.
Geosynthetic-Reinforced Soil (GRS) mass, comprising soil and layers of geosynthetic reinforcement, is not a uniform mass. To examine the behavior of a GRS mass by a laboratory test, a sufficiently large-size specimen of soil and reinforcement is needed to produce a representative soil-geosynthetic composite. This paper presents a generic test, referred to as the Soil-Geosynthetic Composite (SGC) test, for investigating stress-deformation behavior of soil-geosynthetic composites in a plane strain condition. The specimen dimensions, 2.0 m high and 1.4 m wide in a plane strain configuration, were determined by the finite element method of analysis. The configuration, specimen dimensions, test conditions, and procedure of the SGC test are described. In addition, the results of a SGC test with nine sheets of reinforcement, as well as those of an unreinforced soil test conducted in otherwise identical conditions, are presented. In the test, the soil mass was subject to a prescribed value of confining pressure, applied by vacuum through latex membrane covering the entire surface area of the mass in an air-tight condition. Vertical loads were applied on the top surface of the soil mass until a failure condition was reached. The behaviors of the soil masses, including vertical displacements, lateral movement, and strains in the geosynthetic reinforcement, were carefully monitored. The measured data allow the behavior of reinforced and unreinforced soils to be compared directly, provide a better understanding of soil-geosynthetic composite behavior, and serve as the basis for verification of numerical models to investigate the performance of GRS structures. J. Ross Publishing, Inc.
In current design methods for reinforced soil walls, it has been tacitly assumed that reinforcement strength and reinforcement spacing play an equal role. This fundamental design assumption has led to the use of larger reinforcement spacing (0.3-1.0 m) in conjunction with stronger reinforcement to reduce construction time. Recent studies, however, have clearly indicated that the role of reinforcement spacing is much more significant than that of reinforcement strength. With closely spaced (reinforcement spacing <= 0.3 m) reinforcement, the beneficial effects of geosynthetic inclusion is significantly enhanced, and the load-deformation behavior can be characterized as that of a composite material. A reinforced soil mass with closely spaced geosynthetic reinforcement is referred to as geosynthetic-reinforced soil (GRS). In this study, an analytical model is developed for predicting the ultimate load-carrying capacity and required reinforcement strength of a GRS mass. The model was developed based on a semiempirical equation that reflects the relative roles of reinforcement spacing and reinforcement strength in a GRS mass. Using measured data from field-scale experiments available to date, it is shown that the analytical model is capable of predicting the ultimate load-carrying capacity and required reinforcement strength of a GRS mass with good accuracy. (C) 2013 American Society of Civil Engineers.
When an earth fill is subject to loading and subsequent unloading, it will bring about an increase in the lateral stress, provided that there is sufficient constraint to lateral deformation of the soil mass. The increase in lateral stress is commonly known as the "residual" or "lock-in" lateral stress. The residual stress resulted from compaction operation, which involves a series of loading and unloading onto a soil mass, is referred to as "compaction-induced stress" (CIS). The CIS will increase the stiffness and strength of the soil mass, and is an important factor to be considered in the behavior of compacted soil. A number of studies have been conducted on the CIS in an unreinforced soil mass. With a reinforced soil, the CIS is likely to be much more pronounced because there is a higher degree of constraint to lateral deformation in a reinforced soil mass due to soil-reinforcement friction. An analytical model, referred to as the CIS model, is developed for evaluation of compactioninduced stress in a reinforced soil mass. Correlations for determination of model parameters are given so that the parameters can be estimated through reinforcement spacing and stiffness, and common soil parameters, such as the angle of internal friction (Φ), and overconsolidation ratio (OCR). In addition, the stress paths of typical fill compaction operation are discussed, including compaction with a plant moving toward and away from a section under consideration, and compaction with multiple passes. The CIS model presented in this paper is found to give CIS values very close to those obtained from sophisticated finite element analysis of a 6-m high GRS mass under different values of compaction pressure. The CIS in the reinforced soil mass is significant under compaction pressures typically used in actual fill compaction. J. Ross Publishing, Inc.
Two full-scale segmental facing Geosynthetic-Reinforced Soil (GRS) abutment walls, referred to as "the NCHRP test abutments", were constructed and load-tested at the Turner-Fairbank Highway Research Center in McLean, Virginia. The two experiments were conducted to (1) examine the behavior of segmental facing GRS abutment walls under increasing vertical loads on a bridge sill, and (2) furnish a set of well-defined data for verification of analytical models. This paper describes the two experiments and the measured and observed behavior due to the load applications. The behavior of the test walls were discussed and compared with existing performance criteria that were developed based on experience with real bridges. The comparisons were made in terms of maximum sill settlement, maximum angular distortion, and maximum lateral wall movement. In addition, the safety factors and failure loads of the test walls were evaluated by the prevailing design method. The predicted failure loads obtained from the prevailing design method, even with all safety factors and strength reduction factors being set equal to one, were found to be much lower than the measured values, suggesting that the prevailing design method is likely to be overly conservative. J. Ross Publishing, Inc.
Compared to geosynthetic-reinforced soil (GRS) retaining walls, GRS abutment walls are generally subjected to much greater intensity surface loads that are fairly close to the wall face. A major issue with the design of GRS abutments is the allowable bearing pressure of the bridge sill on the abutments. The allowable bearing pressure of a bridge sill over reinforced soil retaining walls has been limited to 200 kPa in the current NHI and Demo 82 design guidelines. A study was undertaken to investigate the allowable bearing pressures of bridge sills over GRS abutments with flexible facing. The study was conducted by the finite element method of analysis. The capability of the finite element computer code for analyzing the performance of GRS bridge abutments with modular block facing has been evaluated extensively prior to this study. A series of finite element analyses were carried out to examine the effect of sill type, sill width, soil stiffness/strength, reinforcement spacing, and foundation stiffness on the load carrying capacity of GRS abutment sills. Based on the results of the analytical study, allowable bearing pressures of GRS abutments were determined based on two performance criteria: A limiting displacement criterion and a limiting shear strain criterion, as well as the writers' experiences with GRS walls and abutments. In addition, a recommended design procedure for determining the allowable bearing pressure is provided.
This paper presents a numerical study of maximum reinforcement tensile forces for geosynthetic reinforced soil (GRS) bridge abutments. The backfill soil was characterized using a nonlinear elasto-plastic constitutive model that incorporates a hyperbolic stress-strain relationship with strain softening behavior and the Mohr-Coulomb failure criterion. The geogrid reinforcement was characterized using a hyperbolic load-strain-time constitutive model. The GRS bridge abutments were numerically constructed in stages, including soil compaction effects, and then loaded in stages to the service load condition (i.e., applied vertical stress = 200 kPa) and finally to the failure condition (i.e., vertical strain = 5%). A parametric study was conducted to investigate the effects of geogrid reinforcement, backfill soil, and abutment geometry on reinforcement tensile forces at the service load condition and failure condition. Results indicate that reinforcement vertical spacing and backfill soil friction angle have the most significant effects on magnitudes of maximum tensile forces at the service load condition. The locus of maximum tensile forces at the failure condition was found to be Y-shaped. Geogrid reinforcement parameters have little effect on the Y-shaped locus of the maximum tensile forces when no secondary reinforcement layers are included, backfill soil shear strength parameters have moderate effects, and abutment geometry parameters have significant effects.
This paper presents a numerical investigation of the deformation and failure behavior of geosynthetic reinforced soil (GRS) bridge abutments. The backfill soil was characterized using a nonlinear elastoplastic constitutive model that incorporates a hyperbolic stress-strain relationship with strain-softening behavior and theMohr-Coulomb failure criterion. The geogrid reinforcement was characterized using a hyperbolic load-strain-time model. The abutments were numerically constructed in stages, including soil compaction effects, and then monotonically loaded in stages to failure. Simulation results indicate that a nonlinear reinforcement model is needed to characterize deformation behavior for high applied stress conditions. A parametric study was conducted to investigate the effects of reinforcement, backfill soil, and abutment geometry on abutment deformation and failure behavior. Results indicate that reinforcement vertical spacing, reinforcement stiffness, backfill soil friction angle, and lower GRS wall height are the most significant parameters. The shape of the failure surface is controlled primarily by abutment geometry and can be approximated as bilinear.
In this study, a three-dimensional (3D) Finite Element (FE) analysis was developed to simulate the fully-instrumented geosynthetic reinforced soil integrated bridge system (GRS-IBS) at Maree Michel Bridge in Louisiana. The 3DFE computer program PLAXIS 3D 2016 was selected to simulate the GRS-IBS behavior under different loading conditions. A second order-hyperbolic elasto-plastic soil model was used to simulate the granular backfill materials. The soil-structure interaction was simulated using zero thickness interface elements, in which the interface shear strength is governed by Mohr-Coulomb failure criterion. Three different loading conditions were considered in this study: (a) at the end of bridge construction (Case 1); (b) surface loading (Case 2); and (c) at abnormal loading (Case 3), which is equal to the dead load of the bridge structure plus three times the service loading. The predicted results were compared with the field measurements at the end of bridge construction. Moreover; the predicted results of the 3D-FE analysis were compared with those predicted using the 2D-FE analysis. A good agreement was obtained between the 3D-FE and 2D-FE numerical results and the field measurements. The predicted results using the 3D-FE showed that the range of maximum reinforcement strain under service loading ranges between 0.6% and 1.5%, depending on the location of the reinforcement layer. The maximum lateral deformation at the face was between 3 mm (0.07% lateral strain) under service load case and 7 mm (0.3% lateral strain) for abnormal load case. The maximum settlement of the GRS-IBS due to the service loading was 9 mm (0.3% vertical strain). The axial reinforcement forces predicted by FHWA (Adam et al., 2011) design methods were compared with those predicted by the 3D-FE and 2D-FE analysis. The results showed that the FHWA analytical method is 1.5–2.5 times higher than those predicted by the FE analysis, depending on the loading condition and reinforcement location.
Geosynthetic reinforced soil integrated bridge system (GRS-IBS) design guidelines recommend the use of a reinforced soil foundation (RSF) to support the dead loads that are applied by the reinforced soil abutment and bridge superstructure, as well as any live loads that are applied by traffic on the bridge or abutment. The RSF is composed of high-quality granular fill material that is compacted and encapsulated within a geotextile fabric. Current GRS-IBS interim implementation design guidelines recommend the use of design methodologies for bearing capacity that are based around rigid foundation behavior, which yield a trapezoidal applied pressure distribution that is converted to a uniform applied pressure that acts over a reduced footing width for purposes of analysis. Recommended methods for determining the applied pressure distribution beneath the RSF for settlement analyses follow conventional methodologies for assessing the settlement of spread footings, which typically assume uniformly applied pressures beneath the base of the foundation that are distributed to the underlying soil layers in a fashion that can reasonably be modeled with an elastic-theory approach. Field data collected from an instrumented GRS-IBS that was constructed over a fine-grained soil foundation indicates that the RSF actually behaves in a fairly flexible way under load, yielding an applied pressure distribution that is not uniform or trapezoidal, and which is significantly different than what conventional GRS-IBS design methodologies assume. This paper consequently presents an empirical approach to determining the applied pressure distribution beneath the RSF in GRS-IBS construction. This empirical approach is a useful first step for researchers, as it draws important attention to this issue, and provides a framework for collecting meaningful field data on future projects which accurately capture real GRS-IBS foundation behavior.
This paper presents the results of a finite element (FE) numerical analysis that was developed to simulate the fully-instrumented Geosynthetic Reinforced Soil Integrated Bridge System (GRS-IBS) at the Maree Michel Bridge in Louisiana. Four different loading conditions were considered in this paper to evaluate the performance of GRS-IBS abutment due to dead loading, tandem axle truck loading, service loading, and abnormal loading. The two-dimensional FE computer program PLAXIS 2D 2016 was selected to model the GRS-IBS abutment. The hardening soil model proposed by Schanz et al., (1999) that was initially introduced by Duncan and Chang (1970) was used to simulate the granular backfill materials; a linear-elastic model with Mohr-Coulomb frictional criterion was used to simulate the interface between the geosynthetic and backfill material. Both the geosynthetic and the facing block were modeled using linear elastic model. The Mohr-Coulomb constitutive model was used to simulate the foundation soil. The FE numerical results were compared with the field measurements of monitoring program, in which a good agreement was obtained between the FE numerical results and the field measurements. The range of maximum reinforcement strain was between 0.4% and 1.5%, depending on the location of the reinforcement layer and the loading condition. The maximum lateral deformation at the face was between 2 and 9 mm (0.08%–0.4% lateral strain), depending on the loading condition. The maximum settlement of the GRS-IBS under service loading was 10 mm (0.3% vertical strain), which is about two times the field measurements (∼5 mm). This is most probably due to the behavior of over consolidated soil caused by the old bridge. The axial reinforcement force predicted by FHWA (Adams et al., 2011b) design methods were 1.5–2.5 times higher than those predicted by the FE analysis and the field measurements, depending on the loading condition and reinforcement location. However, the interface shear strength between the reinforcement and the backfill materials predicted by Mohr-Coulomb method was very close to those predicted by the FE.
This paper presents numerical simulations of the performance of the Geosynthetic Reinforced Soil-Integrated Bridge System (GRS-IBS) under static loading conditions. Simulations were conducted using a finite-difference program and realistic conditions for system geometry, backfill soil, geosynthetic reinforcement, and applied loads. Simulation results, including lateral facing displacements, settlements, lateral and vertical earth pressures, and reinforcement tensile strains and forces, indicate good performance of GRS-IBS during construction and under traffic loads. A parametric study was conducted to investigate the effects of backfill soil compaction, reinforcement length, reinforcement stiffness, bearing bed reinforcement, bridge seat setback distance, bridge load, and abutment height on the performance of GRS-IBS. Results indicate that reinforcement stiffness, bridge load, and abutment height have the most significant influences on lateral facing displacements and bridge seat settlements. Differential settlements between the bridge and approach roadway were small for all conditions.
Geosynthetic-reinforced soil (GRS) integral bridge was developed to overcome several inherent serious problems with conventional type bridges comprising a simple-supported girder (or multiple girders) supported via bearings typically by RC abutments retaining unreinforced backfill (and a pier or piers for multiple girders). The problems include relatively high construction and maintenance costs with relatively long construction time resulting from the use of bearings; massive abutment structures usually supported by piles; bumps immediately behind the abutments; and a relatively low stability of the girders supported by roller bearings and the approach embankment against seismic and tsunami loads. For a GRS integral bridge, a pair of GRS walls (and an intermediate pier or piers if necessary for a long span) are first constructed. After the deformation of the supporting ground and the backfill of the GRS walls has taken place sufficiently, steel-reinforced full-height-rigid (FHR) facings are constructed by casting-in-place concrete on the wall face wrapped-around with the geogrid reinforcement. Finally a continuous girder is constructed with both ends integrated to the top of the FHR facings. The girder is also connected to the top of an intermediate pier, or piers, if constructed. The background and history of the development of GRS integral bridge is described. The first four case histories, one completed in 2012 for a new high-speed train line and the other three completed in 2014 to restore a railway damaged by a great tsunami of the 2011 Great East Japan Earthquake, are reported.
A mechanism for reinforced earth, constructed by introducing thin flat high modulus and strength material layer by layer into the soil, is proposed. This mechanism is based on the change of stress state in the soil induced by the shearing stress on the contact faces between the soil and reinforcement due to difference in their relative rigidity. Laboratory triaxial tests were performed to investigate the deformation and strength characteristics of the reinforced sand. Both short regular triaxial specimens in which the rigid caps were treated as reinforcement and regular triaxial specimens with several horizontal layers of fiberglass nets equally spaced in the horizontal planes were used.
This paper presents a numerical investigation of the performance of geosynthetic-reinforced soil (GRS) bridge abutments under static loading conditions. Simulations were conducted using a finite-difference program to model the Founders/Meadows GRS bridge abutment during construction and service. Simulated results are in good agreement with field measurements, including displacements, lateral and vertical earth pressures, and tensile strains and forces in reinforcement. The simulations also indicate that horizontal restraint from the bridge structure has a significant influence on abutment deflections. A parametric study was then conducted to investigate the performance of a single-span full bridge system with two GRS abutments, including effects of bridge contact friction coefficient, backfill soil relative compaction, backfill soil cohesion, reinforcement spacing, reinforcement length, reinforcement stiffness, and bridge load. Results indicate that backfill soil relative compaction, reinforcement spacing, and bridge load have the most significant influence on lateral facing displacements and bridge footing settlements for GRS abutments. Differential settlements between the bridge footing and approach roadway were small for all simulated conditions.
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Four pairs of large-scale instrumented geosynthetic reinforced soil (GRS) square columnswere load tested to study the effects of varying reinforcement strength to spacing ratio, to discern the lateral pressures during construction and during load testing, and to derive shear strength parameters of the GRS composite. Each pair was identical in every respect, except onewas loaded with a dry-stacked concrete masonry unit (CMU) facing in place and the other without. Lateral pressures during constructionwere found to be small for the facing type used in this study. Also, based on the derived GRS composite shear strength parameters, it was found that (1) the GRS composite Mohr-Coulomb envelopes are not parallel to those for the unreinforced soil; (2) the reinforcement increased the composite cohesion compared to the unreinforced soil (cohesion increases with decreasing spacing and increasing reinforcement strength); (3) the composite friction angle is less than that of the unreinforced soil (friction angle increases with decreasing reinforcement strength and increasing spacing); (4) as the composite friction angle increases, the active lateral earth pressure coefficient decreases; and (5) the benefits of reinforcing a soil become increasingly significant as the reinforcement spacing decreases.
A straightforward analytical method is proposed to calculate the reinforcement loads of vertical-reinforced soil composites before the strength of soil is fully mobilized. The method assumes compatibility of soil and reinforcement deformations along the potential failure surface. It makes use of the nonlinear stress-strain relationship of soil in a plane-strain condition and Rowe's stress-dilatancy relationship. It has the advantage of taking into account the soil dilatancy before failure and can properly estimate the reinforcement load with small or medium soil deformation. The effect of soil compaction on the reinforcement load is taken into account through an elastic unloading/reloading approach. The method was first validated against the results of a calibrated numerical analysis. It was then used to predict the reinforcement loads of two large-scale tests. The proposed method has the potential to fully develop into an analytical method for reinforced soil retaining walls, provided that effects of facing restriction and compaction can be quantified.
A new simple analytical procedure (AASHTO modified) that includes the effect of the induced stress due to backfill compaction for use with conventional design methods of geosynthetic reinforced soil (GRS) walls is proposed. The proposed analytical procedure may be used with any conventional design methods that do not take into consideration the effect of the compaction-induced stress in their calculations. This approach is based on an equation suggested by Wu and Pham (2010) to calculate the increase in lateral stress in a reinforced soil mass due to compaction. Additionally, two numerical procedures for modeling of compaction are described. Analyses using these procedures were performed to evaluate the capability of the proposed analytical procedure. The results were compared with values predicted using the Ehrlich and Mitchell (1994) method, the modified version of the K-stiffness method (Bathurst et al., 2008) and the AASHTO simplified method. The results show that the AASHTO modified method and the numerical analyses, in which the compaction-induced stress was modeled using two distributed loads at the top and bottom of each soil layer, resulted in values of the maximum reinforcement tension, Tmax, that agree with those from the full-scale test and those calculated by Ehrlich and Mitchell (1994). On the other hand, the K-stiffness method under-predicts the measured Tmax values. Moreover, numerical modeling of compaction using a distribution load only at the top of each soil layer overestimated the measurements.
The effects of geosynthetic reinforcement type on the strength and stiffness of reinforced sand were evaluated by performing a series of drained plane strain compression tests on large sand specimens. The reinforcement type is described in terms of the degree of unification of the constituting components (for geocomposites) as well as the tensile strength and stiffness, the covering ratio and others (for geocomposites and geogrids). Sand specimens reinforced with different geosynthetic reinforcement types exhibited significantly different reinforcing effects. A geocomposite made of a woven geotextile sheet sandwiched firmly with two sheets of non-woven geotextile, having a 100% effective covering ratio, exhibited reinforcing effects higher than typical stiff and strong geogrids. With some geocomposite types, the reinforcing effects increase substantially by better unifying longitudinally arranged stiff and strong yarns and non-woven geotextile sheets. When fixed firm to the yarns, the non-woven geotextile sheets function like the transversal members of a geogrid by locally transmitting load activated by interaction with the backfill to the yarns. These geocomposites can exhibit reinforcing effects equivalent to those with stiff and strong geogrids. Local strain fields of the specimens are presented to show that, for reinforced sand, the peak stress state reached is always associated with the development of shear band(s) in the sand and a higher peak strength is achieved when the strain localisation starts at a larger global axial strain due to better reinforcing effects.
The geosynthetic reinforced soil (GRS) performance test (PT), also called a mini-pier experiment, was developed by the Federal Highway Administration (FHWA) to evaluate the material strength properties of GRS composites built with a unique combination of reinforcement, compacted fill, and facing elements. The PT consists of constructing a 1.4-m square column of alternating layers of compacted granular fill and geosynthetic reinforcement with a facing element that is frictionally connected up to a height of 2 m, then axially loading the GRS mass while measuring deformation to monitor performance. The results can be directly used in the design of GRS abutments and integrated bridge systems. Considering that the geometry of the PT is square in plan, the equivalency of the results to a bridge application, which more resembles a plane strain condition, is evaluated and presented in this paper. The analysis indicates that the PT closely approximates the bearing resistance, or capacity, of a typical GRS abutment, and is a conservative estimate when predicting stiffness. These results indicate that the PT can be used as a design tool for GRS abutments at both the strength and service limit states.
This paper presents a physical model study of the influence of compaction on the behavior of geogrid-reinforced soil walls. Experiments were accomplished in a facility at the Geotechnical Laboratory of COPPE/UFRJ. For soil compaction, two different types of hand-operated compactors were used: a vibrating plate and a vibratory tamper. Equivalent vertical stresses for the vibrating plate (referred to as the “light compactor”) were much lower than the corresponding value of the vibratory tamper (referred to as the “heavy compactor”). Mobilized tension along the reinforcements and external and internal displacements of the wall were monitored. The results showed that the effect of soil compaction is not limited to a reduction of the soil void ratio. Compaction has led to a significant increase in the horizontal stress inside the reinforced soil mass and generates a kind of pre-consolidated material. Analyses of results showed that compaction has played a decisive factor in terms of the reinforcement tensions and post-construction displacements. The connection load was much less in a wall with heavy compaction than that in a wall with light compaction. Results also showed that the position of maximum tensile force mobilized in the reinforcements was nearer to the face in the wall with heavy compaction. On the other hand, the mobilized tension measured along the reinforcement layers at the end of construction in the wall where heavy soil compaction was used was much higher than the values of tension measured in the wall where light soil compaction was applied. Nevertheless, it was observed that the difference in the mobilized tensions in the reinforcements of these two walls decreased with increase in the value of the external surcharge load.
Analytical models and procedures are presented for the evaluation of peak and residual compaction-induced lateral earth pressures either in the free field or adjacent to vertical, nondeflecting soil-structure interfaces. A hysteretic model for the stresses generated by multiple cycles of loading and unloading is presented, along with recommendations regarding the determination of suitable model parameters. This model is then adapted to incremental analytical methods for the evaluation of peak and residual earth pressures resulting from the placement and compaction of soil. Compaction loading is considered as a transient moving surficial load of finite lateral extent. Simplified hand calculation procedures are presented for cases in which all soil layers are identically compacted. Finally, a series of case studies are presented in which analytical results are compared with full-scale field measurements in order to verify these analytical methods.
Bridge abutments made of geotextile-reinforced soil have been shown to support the bridge load without the use of piles. However, current design procedures are considered to be conservative. To determine the strength, and to understand better the behavior of reinforced soil, large unconfined cylindrical soil samples reinforced with geosynthetics were axisymmetrically loaded. Samples were 2.5 ft (0.76 m) in diameter and 5 ft (1.52 m) in height. Peak strengths of 4.8 kips/ft 2 (230 kPa) to 9.6 kips/ft 2 (460 kPa) at 3% to 8.5% vertical strain were obtained from cylinders reinforced with geotextiles at 6-in. (152-mm) vertical spacing. A strength reduction occurred after the peak strength, but most of the loads were sustained up to at least 10% strain before yielding. Tension in the reinforcement appears to be mobilized first in the middle layers, as determined from the location of tears in the geotextile. An equation to calculate the tensile force in the reinforcement, T max, in a reinforced bridge abutment is proposed. The normalized strains led to the development of the strain distribution factor incorporated in the proposed equation. The proposed equation is slightly more conservative or almost equal, depending on the type of facing, when compared with the K o-stiffness method, but gives values approximately one-half of those obtained using the National Concrete Masonry Association and FHWA Demonstration Project 82 methods.
A Finite Element procedure was used to investigate the reinforcement load and the deformation mode for geosynthetic-reinforced soil (GRS) walls subject to seismic loading during their service life, focusing on those with marginal backfill soils. Marginal backfill soils are hereby defined as filled materials containing cohesive fines with plasticity index (PI) >6, which may exhibit substantial creep under constant static loading before subjected to earthquake. It was found that under strong seismic loading reinforced soil walls with marginal backfills exhibited a distinctive “two-wedge” deformation mode. The surface of maximum reinforcement load was the combined effect of the internal potential failure surface and the outer surface that extended into the retained earth. In the range investigated, which is believed to cover general backfill soils and geosynthetic reinforcements, the creep rates of soils and reinforcements had small influence on the reinforcement load and the “two-wedge” deformation mode, but reinforcement stiffness played a critical role on these two responses of GRS walls. It was also found that the “two-wedge” deformation mode could be restricted if sufficiently long reinforcement was used. The study shows that it is rational to investigate the reinforcement load of reinforced soil walls subject to seismic loading without considering the previous long-term creep.
The effects of compaction at various levels of fill behind a retaining wall are considered analytically. The formulation is adapted for numerical solution and applied to cantilever and foundation walls with different fill geometries and properties. The resulting wall deflexions and earth pressure magnitudes and distributions considerably modify the ‘at-rest’ pressure and are practical significance.
On examine d'une façon analytique l'effect du compactage à divers niveaux de remblai posé derrière un mur de soutènement. On adapte cette formula afin de l'utiliser pour une solution numérique et on l'applique aux murs de fondations et en porte à faux à compactage variable en géométrie et en étéments. Les déflexions du mur et les diverses magnitudes de pression et de distribution qui en résultant amènent une modification considérable aux pressions ‘au repos’. On peut en tirer de conclusions pratiques.
This paper synthesizes the measured behavior and experiences gained from case histories of geosynthetic-reinforced soil (GRS) bridge-supporting structures with “flexible” facings. Only bridge-supporting structures with wrapped-face, modular block face, and rock face are included in the synthesis. The case histories were grouped into two categories: in-service structures and field experiments. Four in-service structures and six full-scale field experiments from the US and abroad were reviewed. All the structures have been instrumented to monitor their performance under applied loads, with some being loaded to failure. The essential features and performance of each case history are briefly described in the paper. A table summarizing the main features of the GRS bridge-supporting structures is also presented. The table shows comparisons of the bridge-supporting structures in terms of wall height, backfill, reinforcement type, reinforcement spacing, facing type and connection, ratio of reinforcement length to wall height, maximum settlement of the loading slab, maximum lateral movement of the wall face, maximum reinforcement strain, and failure surcharge pressure. Based on the measured performance of the case histories, observations are made in relation to performance, design, and construction of GRS bridge-supporting structures.
In order to develop a method of predicting the bearing capacity of horizontal sandy ground reinforced with tensile-reinforcement layers horizontally placed beneath a footing, a series of plane strain model tests with a strip footing was performed. The effects of the length, the arrangements and the rigidity and rupture strength of reinforcement were examined systematically. The strain fields in sand, the tensile forces in reinforcement and the distribution of contact pressure on footing were measured.Even by means of reinforcement layers with a length similar to the footing width, the bearing capacity increased remarkably. Also, the portions of reinforcement layers located outside the footing width contributed to the increase in the bearing capacity only in a secondary way. The bearing capacity of reinforced sand was found equal to the smaller of the following two values; the one controlled by the failure of the reinforced zone immediately beneath the footing and the other by the failure of sand beneath the reinforced zone.Based on the test results, a method of stability analysis by the limit equilibrium method was developed, taking into account the effects of the arrangement and properties of reinforcement and the failure modes of reinforced sand. The predicted values were well in accordance with the measured ones.
Field tests of segmental block-faced geosynthetic-reinforced soil (GRS) bridge abutments and piers have demonstrated excellent performance characteristics and very high load carrying capacity. One important feature of GRS abutment is that it can potentially eliminate the use of piling when situated over a weak foundation. This will not only reduce the costs but also reduce “bridge bumps” often experienced at the ends of a bridge resting on a pile-supported abutment. This study was undertaken to investigate the potential of GRS bridge abutments to alleviate bridge approach settlements. The study was conducted by the finite element method of analysis using the computer program DACSAR. The program was first calibrated by comparing its results with the measured data of the Founders/Meadows bridge abutment recently constructed by the Colorado Department of Transportation. A parametric study was then conducted to examine the effects of different foundation soils, ranging from loose sand to stiff clay, on the performance of a GRS abutment. Special attention was placed on the maximum vertical and horizontal movements of the abutment as well as the approach settlement characteristics. The study indicated that the finite element computer code DACSAR is a reliable analytical tool for analyzing the performance of GRS bridge abutments and that the GRS abutment is an effective means to reduce differential settlements between the abutment and the approach embankment.
Thesis (Ph. D. in Civil Engineering)--University of California, Berkeley, Dec. 1988. Includes bibliographical references (leaves 282-283).
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