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Centrifuge and theoretical modelling of conical footings on sand
... It accounts for the initial lateral 'breakout' force and a constant residual force developed immediately after breakout, but it neglects the increasing soil resistance developed during large-amplitude cyclic lateral displacements of the pipe. More recent works have attempted to describe the transverse load-displacement response in the framework of macro-element plasticity modelling, which has previously been used for various types of shallow foundation on sand (Schotman, 1989;Tan, 1990;Nova & Montrasio, 1991;Gottardi et al., 1999). Following an early demonstration of the macro-element approach for pipes on clay (Schotman & Stork, 1987), macro-element models for pipes on sand have been developed by, among others, Zhang et al. (2001Zhang et al. ( , 2002aZhang et al. ( , 2002b, Cassidy (2011) andSandford (2012). ...
... The purpose of this 'sideswipe test' simulation was to define the yield surface, or bearing capacity envelope, in the vertical and horizontal (V, H ) load space. Experiments on shallow foundations under combined (V, H ) loading have shown that the load path during a sideswipe test tracks through a series of yield surfaces (Tan, 1990). This is because as V reduces, downward plastic displacements develop to balance upward elastic displacements (to maintain Δw = 0), and the downward plastic displacements cause hardening or expansion of the yield surface (Tan, 1990;Martin & Houlsby, 2000, 2001. ...
... Experiments on shallow foundations under combined (V, H ) loading have shown that the load path during a sideswipe test tracks through a series of yield surfaces (Tan, 1990). This is because as V reduces, downward plastic displacements develop to balance upward elastic displacements (to maintain Δw = 0), and the downward plastic displacements cause hardening or expansion of the yield surface (Tan, 1990;Martin & Houlsby, 2000, 2001. In typical pipe-soil interaction problems, the virgin penetration (plastic) stiffness is much smaller than the vertical unload-reload (elastic) stiffness. ...
Realistic modelling of transverse (i.e. vertical and lateral) pipe–soil interaction plays an important role in predicting the behaviour of untrenched offshore pipelines that are designed to undergo controlled lateral buckling. The large plastic soil deformations and surface geometry changes that occur during this process mean that numerical analyses using the continuum-based finite-element method are difficult and computationally expensive. Furthermore, most previous research in this area has focused on undrained deformation of soft clay seabed soils. This paper uses the three-dimensional distinct-element method (DEM) to investigate the behaviour of a pipe segment that is partially embedded in sand. The simulation approach is validated against experimental results for a monotonic vertical penetration test, a monotonic sideswipe test, and a cyclic lateral loading test performed under constant vertical load. Other DEM analyses are performed to illustrate the growth, deposition and collection of soil berms, and to investigate the effect of varying the initial vertical overloading ratio and the pipe weight. The DEM simulations provide quantitative predictions of the vertical and horizontal forces acting on the pipe segment, and of the pipe displacement trajectory. Valuable qualitative insights into soil failure mechanisms occurring at a grain level are also obtained.
... According to Tan (1990), Bransby and Randolph (1998), when analyzing numerical models, composite loads applying on structure are controlled by displacement-controlled through vertical displacement (W), horizontal displacement (u) and rotational displacement (T). These loads are assigned to the reference point (LRP). ...
... The reaction force which could be obtained at the loading point include: vertical load (V), horizontal load (H) and moment (M). To plot a failure evelope in three dimensions, there are two displacement controlled method that could be used: (1) probe analysis, Bransby and Randolph (1998) and (2) swipe analysis, Tan (1990). a. Method 1: probe analysis is also known as fixed displacement analysis. ...
... b. Method 2: swipe analysis was first presented by Tan (1990) based on centrifuge experiments. This method consists of two stages. ...
Movable dam is one of river barriers that has been studied and applied effectively in the Mekong Delta. The principle of increasing the stability of the dam by enlarging foundation width to reduce the normal pressure so that the dam could be placed directly on soft clay soil without soil improvement. The characteristic of the movable dams is low vertical loading, large horizontal loading and moment. Bearing capacity of strip footing under eccentric and inclined loads subjected to combined loading V: H: M is extremely complicated. In the case of the movable dam, it is difficult to evaluate bearing capacity on soft soil because of low vertical loading but high eccentric and inclined ones. On the other hand, the soil-structure interaction is also difficult to analyze. This study presents the bearing capacity of movable dam footing on clay subjected to combined load V:H:M that is based on failure envelope by numerical analysis and compare the results with previous researches. The authors also present method to check the stability of movable dams on soft clay soils subjected to combined load in Mekong Delta.
... The failure envelope is a hypersurface that defines the n-dimensional combination of loads (n ! 1) that results in the ultimate limit state (or plastic failure) of a foundation. The advantages of this approach over classical bearing capacity methods (Terzaghi, 1943;Meyerhof, 1951;Vesić, 1973) are manifold and have been widely discussed (Schotman, 1989;Tan, 1990;Nova & Montrasio, 1991;Gottardi & Butterfield, 1993;Bransby & Randolph, 1998;Martin & Houlsby, 2000;Houlsby & Byrne, 2001;Gourvenec, 2007). ...
... The original form of the single swipe test, also known as the sideswipe test, was introduced by Tan (1990) to investigate the VH failure envelope of a surface foundation using centrifuge model tests. In a sideswipe test, the foundation is first pushed vertically to a prescribed embedment, after which the vertical displacement is held constant while the foundation is 'swiped' horizontally. ...
... A fundamental assumption underpinning this type of test is that the swipe phase results in a load path that tracks closely along the failure envelope, using analogies with hardening plasticity theory as applied in critical state soil mechanics (e.g. see the discussions in Tan (1990), Martin (1994) and Martin & Houlsby (2000)). Unfortunately, this assumption does not always hold when generalised single swipe tests are applied to shallow foundations, as the load path may deviate inside (or cut across) the failure envelope and thus underpredict the capacity (Bransby & Randolph, 1998). ...
The failure envelope approach is commonly used to assess the capacity of shallow foundations under combined loading, but there is limited published work that compares the performance of various numerical procedures for determining failure envelopes. This paper addresses this issue by carrying out a detailed numerical study to evaluate the accuracy, computational efficiency and resolution of these numerical procedures. The procedures evaluated are the displacement probe test, the load probe test, the swipe test (referred to in this paper as the single swipe test) and a less widely used procedure called the sequential swipe test. Each procedure is used to determine failure envelopes for a circular surface foundation and a circular suction caisson foundation under planar vertical, horizontal and moment (VHM) loading for a linear elastic, perfectly plastic von Mises soil. The calculations use conventional, incremental-iterative finite-element analysis (FEA) except for the load probe tests, which are performed using finite-element limit analysis (FELA). The results demonstrate that the procedures are similarly accurate, except for the single swipe test, which gives a load path that under-predicts the failure envelope in many of the examples considered. For determining a complete VHM failure envelope, the FEA-based sequential swipe test is shown to be more efficient and to provide better resolution than the displacement probe test, while the FELA-based load probe test is found to offer a good balance of efficiency and accuracy.
... In cases of combined V-H-M loading, portions of the vertical capacity were distributed (V/V 0 = 0, 0.25, 0.5, and 0.75) onto the ring foundation surface, followed by various fixed ratios of H-M loads to assess different H-M combinations at failure under varying vertical loads. This approach has been well documented in the literature by Gourvenec and Randolph (2003), Bransby and Randolph (1998), Tan (1990), Chen et al. (2022), and Shen et al. (2016). ...
... This methodology has been widely applied to several geotechnical stability problems by Shiau et al. (2018Shiau et al. ( , 2022Shiau et al. ( , 2023. In view of the computation process, the limit load (V 0 ) was initially assessed under a solely vertical load condition before proceeding with the V-H analysis (Tan, 1990). This process yields the limiting vertical loads (V 0 ) for different r e and r i /r o values, as shown in Table 1. ...
This paper is concerned with the assessment of V-H-M failure envelopes of ring foundations subjected to general loadings on anisotropic clay using adaptive three-dimensional finite element limit analysis (3D AFELA). The 3D analysis involves calculations of the bearing capacity of ring surface foundations for individual vertical force (V), horizontal force (H), and moment (M) using the well-known anisotropic undrained shear (AUS) failure criterion to study the effect of clay anisotropy. Accordingly, the combinations of V-H, V-M, and H-M load spaces are examined with the use of normalized output parameters (V/s uTC A, H/s uTC A, and M/s uTC AB) and two dimen-sionless input parameters, including the radius coefficient (r i /r o) and the anisotropic factor (r e). Furthermore, the various characteristics of the failure mechanisms are examined. The study continues with artificial neural network (ANN) models, aiming to evaluate the correlation between input parameters and their corresponding outcomes. Three optimization methods based on metaheuristic algorithms are considered: artificial bee colony (ABC), imperialist competitive algorithm (ICA), and artificial lion optimization (ALO). The ANN-ICA model stands out for its exceptional predictive precision, robustness, and top-ranking efficiency in score analysis. The outcome of the study proves to be both effective and efficient for evaluating the 3D failure envelope of ring foundations on anisotropic clay subjected to combined loadings (V-H-M).
... The procedure is based on experimental or numerical displacement-controlled tests and allows direct investigation of the shape and size of the failure surface for a given foundation. It has been introduced experimentally using centrifuge tests by [102] to investigate the V À H failure envelope of a shallow foundation. Subsequently, this approach gained widespread recognition and was popularized in the field, notably through the experimental studies of [22,51,52,82] and [83]. ...
... In swipe tests, the response of foundations under various loads by displacement-controlled tests is explored. The load path effectively traces along the contours of the failure envelope [51,56,96,102]. In the following, swipe tests are numerically reproduced using a 3D nonlinear FEM model. The sign conventions for the loads (V, M, H) and the vertical displacements, the rotations and the horizontal displacements (w, h and u, respectively) are presented in Fig. 1, based on Butterfield et al. [21]. ...
The paper focuses on the identification of the 3D failure envelope of a shallow foundation on soft soil reinforced by rigid inclusions. A nonlinear 3D finite element model is first validated against literature results and novel centrifuge experimental data. The failure envelope, defined in the vertical force (V), bending moment (M) and horizontal force (H) space, is then constructed using numerical swipe tests. Analytical formulas are introduced to describe the 3D failure envelope shape and inclination, considering the influence of the coverage area, the thickness, and the friction angle of the load transfer platform. Finally, the efficiency of a rigid inclusion foundation is highlighted by comparing its failure envelope to that of the same foundation without rigid inclusions. The proposed analytical failure envelope can be used by engineers to quantify the bearing capacity of rigid inclusion foundations and by researchers to develop novel macroelements submitted to complex coupled loads.
... The undrained capacity of individual footings such as spudcans or buckets undergoing combined V-M-H loading is expressed in terms of a yield locus where f(V,M,H) = 0 at yield (e.g. Murff 1994, Tan 1990, Martin 1994, Bransby & Randolph 1998. With a suitable plastic potential and hardening rule, the footing behaviour can be modelled in a work-hardening plasticity framework (e.g. ...
... With a suitable plastic potential and hardening rule, the footing behaviour can be modelled in a work-hardening plasticity framework (e.g. Tan 1990, Martin 1994. ...
... On the other hand, various other studies have presented twodimensional and three-dimensional parabolic failure envelope curves due to V-M-H loads for a different type of footings and shallow foundation system (Roscoe and Schofield, 1957;Tan, 1990;Houlsby, 1997;Bransby and Randolph, 1998;Gourvenec and Randolph, 2003;Bienen et al., 2006;Zhang et al., 2011;Li et al., 2017). The exploration of the shape of the failure envelope or yield surface within three-dimensional V-M-H load space was first introduced by Roscoe and Schofield (1957). ...
... Butterfield and Ticof (1979) used the concept of Ticof (1977) and developed a three-dimensional 'cigar-shaped' parabolic yield surface within V-M-H load space. Further, Tan (1990) investigated the V-H yield loci for various conical and spudcan footings resting on saturated sands by performing displacement controlled 'side-swipe' tests in a geotechnical centrifuge. The benefit of this swipe test is that a complete failure locus on a certain plane can be determined in a single test. ...
A combined piled raft foundation (CPRF) is generally used for massive and tall structures. The conventional design of piled raft does not include the capacity of piled raft under combined lateral and vertical load. However, vertical (V), horizontal (H) and moment (M) loading may act on the foundation simultaneously. The present study examines the behaviour of piled raft foundation in sandy soil under V-M-H interaction using three-dimensional finite element analysis. The horizontal and moment capacity of piled-raft is assessed due to various influential parameters, such as relative stiffness of pile and soil, raft-soil relative stiffness, spacing to diameter ratio of the pile, length to width ratio of the foundation and pile head connection with the raft. It is observed that piled-raft lateral capacity increases due to combined loading than that of independent capacity. Both failure and design envelopes are also developed considering V-M-H interaction. Finally, the design implication of the outcome of the present study is presented using a case study. It is revealed that the design of piled raft with lateral capacity obtained from the combined action of the V-M-H load may reduce the number of piles as compared to conventional design performed using individual capacity.
... In a sideswipe test, a foundation is pushed vertically until it reaches a certain penetration or load (normally associated with a given plastic penetration, w p ), and then is moved horizontally while keeping its penetration constant. The resulting load path is expected to track across the yield surface at the given penetration (e.g., Tan 1990;Martin 1994), thereby defining the shape of the yield surface for a given plastic penetration (w p ) and associated vertical capacity (V 0 ). It should be noted that this interpretation is only valid when the assumption about the hardening law being solely related to w p is acceptable (and elastic displacement components are negligible) and this will be explored when interpreting the tests. ...
... Fig. 6 summarizes the load paths from these sideswipe tests with the horizontal and vertical loads normalized by V i , which for the normally loaded condition has the same value as V 0 as defined in Eq. (3) [ Fig. 6(a)] and when normalized by the peak vertical capacity of the foundation, V m [ Fig. 6(b)]. It is noteworthy that all tests feature some initial vertical load reduction (for example about 10% for the test with the largest V i ), because of creep relaxation of the sand during the time required in the tests between the end of vertical penetration and the beginning of the horizontal displacement phase (Tan 1990;Govoni et al. 2010). Fig. 6(a) shows that the shape of load path from the caisson sideswipe tests is not constant and does not isotropically scale with V 0 , with a particularly different shape found for caisson under low initial vertical loads. ...
This paper presents the development of an improved plasticity model to define the combined vertical and horizontal capacity of suction caisson in sand under low vertical loads, conditions relevant for foundations of offshore wind turbines. Model tests following a variety of load paths were used to demonstrate the change of the shape of the yield surface as a function of the vertical load applied and to provide parameters for plasticity modelling. A new hardening law is proposed that accounts for capacity changes because of caisson lateral movement in addition to the vertical movements normally solely considered. An updated formulation for the yield surface is then presented based on a normalization by the new hardening parameter. The plastic model is subsequently validated by comparison with test results. The model can be used to assist in the prediction of the capacity of suction caisson under combined loading at low vertical loads.
... The soil used in the centrifuge tests was Hostun sand, acquired from the area of Drôme in the southeast of France. This sand has been regularly used in centrifuge tests at the Schofield Centre of the University of Cambridge [19][20][21][22] and in several other European centres. The sand contains a high percentage of silica (SiO 2 > 98%) and has a grain shape varying from angular to sub-angular. ...
... Equations (16) to (18) were developed for seismic applications and equations (19) and (20) were deduced specifically for wind turbine structures. The amplitude of vibration is very different from seismic application because the amplitude of vibration of a wind turbine is very small. ...
... There are mainly two methods to acquire the failure envelope of the FBJF, i.e., the swipe loading method and the fixed-displacement ratio method [29,46,47]. The swipe loading method requires high symmetry of the envelope and is relatively simple. ...
As offshore wind farms move into deeper waters and the capacity of offshore wind turbines (OWTs) increases, a new type of OWT foundation needs to be developed. In this study, a new type of five-bucket jacket foundation (FBJF) was proposed based on the broad application of a multi-bucket jacket foundation (MBJF) in offshore wind farms. The soil around the OWT foundation is subject to scour due to the complex marine environment. To investigate the effects of scouring on the FBJF, a series of local-scour simplified finite-element models of the FBJF were established using ABAQUS, and the effects of scouring depth and the extent on the bearing capacity of the FBJF with the monotonic load were analyzed. Then, the failure envelopes of the FBJF under combined loading were obtained using the fixed-displacement ratio method, and the effects of various scour conditions on the failure envelopes were compared. The results indicate that the failure envelope profile contracts inward, and the bearing capacity decreases with the increasing scouring depth and extent. Furthermore, the failure envelopes of the FBJF under different vertical loads were calculated, and the FV-FH-FM failure envelopes of the FBJF were obtained through interpolation. Finally, the effects of different scour conditions on the FV-FH-FM failure envelopes of the FBJF were analyzed. The results show that the FV-FH-FM failure envelopes of the FBJF have similar profiles and follow the same trend under different scour conditions.
... In order to determine the ultimate combined resistance of a shallow foundation reinforced by RIs, the displacement-controlled swipe test methodology is adopted. The fundamental idea comes from analogies with the hardening plasticity theory applied in critical state soil mechanics [5], in which the result is a load path that tracks along with the failure envelope (e.g., discussed in [6,7,8]). The sign conventions and the example of a load sweep in the − space are shown in Figure 4. ...
... Analogous to the critical state in critical soil mechanics, the so-called parallel point has been proposed in strain hardening models of SFS response; its occurrence upon constant vertical loading and deformation causes the footing to rotate or translate laterally (i.e., at a certain transition point between the punching shear and uplifting where the sliding mechanism predominantly occurs). The parallel point, also defined as the peak state of the potential surface in the V-planes, adopted in several experimental studies (e.g., 50 ), where the foundation can rotate or translate laterally but cannot move upward or downward, is also examined herein to track the potential function envelope and especially to determine a suitable mathematical law for the direction of the plastic strain increments at failure. However, the conditions described above can likely be associated only with the failure surface, due to the occurrence of large deformations upon foundation failure. ...
With the shift of the offshore wind energy sector to deeper waters, demand for the development of more complex foundation solutions, particularly suction bucket–supported tripod/tetrapod and jacket foundations, has increased.
This paper is divided into two main sections. The first part comprises a comprehensive review of the performance of circular surface and shallow foundations under combined loading (VHM), and how it can principally be understood in a theoretical framework of plasticity theory. Examination of the considered data suggested that the general assumption of over-estimated non-association degree with constant failure surface parameters and increasing vertical load may require further investigation. This may be attributed to the complex interplay of multiple properties such as stress level, soil strength profile and foundation geometry. The existing data in the literature were also used to provide practical guidance for a successful implementation of the elasto-plastic constitutive relationships in offshore foundation design.
In second part of the paper, the suitability of the non-associated plasticity formulation for a baseline multi-pod system in H-M load space was investigated using three-dimensional finite element (FE) analyses and not verified. Furthermore, the failure envelopes and hardening law for caissons with different embedment ratios differed from those recommended in the literature were established. Parametric studies of multi-caisson foundations revealed that the failure mechanism of multi-bucket foundations under horizontal loading depended greatly on the bucket spacing. The horizontal bearing capacities increased with the bucket spacing until they reached a threshold. Meanwhile, analyses of the multi-bucket foundation under moment loading confirmed the occurrence of a push-pull failure mechanism.
... The load paths generated in these probe tests start from the origin and then follow the failure envelope upon reaching the failure point. In this study, the authors preferred displacement probe test over swipe test (Tan 1990) or recently developed modified-swipe test (Shen et al. 2017) in obtaining V-H and V-M failure envelopes. This is because the swipe test, although capable of producing the entire failure envelope by performing two consecutive loading steps, is believed to undercut the envelope for greater embedment (Gourvenec 2008). ...
Deeply embedded caissons with a significantly large diameter, widely used as bridge foundation elements, are generally subjected to the complex combinations of several environmental and operational forces. The undrained capacities of rigid caisson foundations embedded in soils with increasing strength with depth and under combined loading are investigated using finite-element analyses. Estimation of uniaxial capacities followed by biaxial failure envelopes is carried out to capture the effect of vertical load on ultimate transverse capacities. Two-dimensional failure envelope in H-M loading space is presented to define the combined ultimate loading state of the circular caissons where the shape of the envelope is illustrated by a series of closed form expressions. The trajectory of the V-H-M failure envelope obtained from numerical analysis is validated by the mechanisms of upper bound limit analysis. Finally an example problem is provided to showcase the applicability of the expressions proposed to execute the design approach.
... Moreover, repeating the above procedure until the specified maximum displacement value is exceeded. The combined loading tests are carried out by using the swipe method (Tan 1990) under the two loading sequences of H!T and T!H. The detailed description of the entire test procedure is shown in Table 3. Figure 5 shows the load-displacement relationship of the hybrid foundation measured from the independent horizontal load tests. ...
The monopile-friction wheel hybrid foundation withstands various loads in the marine environment , such as the vertical load (V) transmitted from the superstructure, horizontal loads (H) caused by wind or wave, torsional loads (T) caused by rotating structures. In this article, 1 g model tests are used to investigate the behavior of the monopile-friction wheel hybrid foundation under independent horizontal load (H) or torsional load (T), and combined loads (H-T) in sand soil, respectively. The failure envelopes of H-T loading plane are obtained from the measured load-displacement data with the simplified calculation equations presented as well. Finally, we also discuss quantitatively the influences of the pre-vertical loads, foundation geometry and loading eccentricity on the bearing capacity of the hybrid foundation via the three-dimensional finite element method. The results indicate that the displacement response of the hybrid foundation under independent loading is significantly different from that subjected to combined loads (H-T). The torsional bearing capacity of the hybrid foundation can be significantly improved by 6.6-33.34% under pre-horizontal load. The horizontal bearing capacity of the hybrid foundation decreases sharply after the pre-torsional load reaches a certain value, which decreases by about 20%. The presence of a friction wheel improves the torsional/bending moment distribution of pile shaft. ARTICLE HISTORY
... Two approaches, namely, the swipe test and the fixed-ratio test, are adopted to analyse the failure envelopes under combined loading conditions. In the swipe test (Tan 1990), the tracks are initially loaded to vertical bearing failure, and then the tracks are "swiped" either horizontally or in rotation while the vertical displacement is maintained. This allows for the determination of the load path close to the true failure envelope in a single test. ...
Tracked vehicles are widely deployed for heavy lifting and transportation on inaccessible terrains such as swamps, bogs, and peatlands. The stability of a tracked vehicle is traditionally assessed only under uniaxial loading conditions and the impact of combined loading from different directions is ignored. This makes the conventional design framework somewhat unreliable. The failure envelope approach has been widely employed to assess the load-carrying capacity of shallow foundations. However, the failure envelopes available in public domain mainly focused on single isolated foundations, ignoring the interference effect between the tracks due to the rigid connection of the vehicle. This paper aims to develop an integrated framework to assess the stability of a tracked vehicle on a soft soil under fully three-dimensional loading conditions. The finite element method is adopted to simulate the soil–vehicle interactions, with the tracks idealised as two shallow foundations in parallel. The stability of the foundation system is described in terms of failure envelopes considering various track configurations and load combinations. Failure envelopes are represented by expressions and ultimately integrated into a multiple-nested function to determine the overall stability factor. The framework is demonstrated by a case study of designing a tracked vehicle under combined loading conditions.
... The probe test is featured with fixed-ratios of displacement, i.e., the chain segment is loaded with the tangential and normal displacement increments, du and dw, applied proportionally. As suggested by Tan [25], the swipe test is implemented by the swipe-loading path. It consists of two steps: the chain segment is moved in the normal direction until the ultimate normal resistance is achieved, and; a tangential displacement is subsequently imposed while the normal displacement remains zero. ...
The soil resistances along the embedded ground chain affect the pull-out capacity of anchor as they determine the magnitude and direction of tension at the padeye. To facilitate analyses, the chain was usually simplified as a cylindrical line. The chain segment with actual geometry, buried deeply in clayey soil, is studied using a large deformation finite element approach to overcome severe distortion of soil elements around the chain. The uniaxial resistances obtained by the large deformation analyses are verified by comparison with the existing model tests and simplified solutions, followed by presentation of the yield envelope against combined loading. Both the probe test and swipe test are used to form the yield envelopes, and their results have good consistency. The influence of roughness of chain–soil interface on the soil resistances is quantified as well. It is found that the envelope of the chain segment with actual geometry is smaller than that against the simplified cylindrical shape; therefore, the most convenient design may not be the safest option.
... The swipe-testing approach has been applied extensively (experimentally and numerically) to derive combined loading yield surfaces of various foundation schemes, especially for offshore applications. Introduced by Tan (1990), the 'side-swipe' test was based on the analogy between undrained triaxial testing of pre-consolidated samples and lateral displacement testing of vertically preloaded foundations, under conditions of zero settlement and rotation. The load path of such a test was argued to closely track the yield surface in the V ÀH load space, for a given foundation penetration. ...
Motivated by the need to develop rational design methods for the retrofit of existing bridges on pile groups, the paper introduces recent experimental developments at the ETHZ Drum centrifuge. Four setups are developed for vertical, pushover, combined, and vibration testing. Their capabilities and limitations are demonstrated using as example a 2x1 pile group on dense saturated sand. Single piles are subjected to vertical loading, exploring the role of installation effects and interface roughness. Pushover loading is employed to measure the moment capacity (M ult ) of a lightly- and a heavily-loaded group. In contrast to intuitive expectations, the heavily-loaded system mobilises larger M ult . The developed combined loading apparatus is proof-tested for a shallow foundation. Combined loading under constant vertical load is conducted to derive failure envelopes, revealing significant coupling between lateral and moment loading, and confirming the expansion of the failure envelope with increasing static vertical load. The vibration testing setup is proof-tested, confirming the possibility to identify the natural frequency of the system and the small-strain stiffness of the foundation through non-destructive testing. Although the study is fuelled by our ongoing work on pile groups, the developed experimental setups are of general applicability for the study of deep and shallow foundation systems.
... Therefore, a homogenous soil layer has been modelled numerically to be representative of Leighton Buzzard sand, fraction E of the following soil geotechnical properties: γ s = 2647 kg/m 3 , e min = 0.613, e max = 1.014, D 10 = 0.095, D 50 = 0.14 (Tan, 1990). The initial K 0 condition has been assumed to be equal to 0.5 as deemed appropriate for dry sand at low mean effective stresses (Stroud, 1971). ...
High-frequency motion is often observed in small-scale experimental works carried out in flexible containers under simplified seismic loading conditions when single harmonic sine input motions are introduced at the base of a soil specimen. The source of the high-frequency motion has often been sought in experimental inaccuracies. On the other hand, the most recent numerical studies suggested that high-frequency motion in the steady-state dynamic response of soil subjected to harmonic excitation can also be generated as a result of soil elastic waves released in non-linear hysteretic soil upon unloading. This work presents an example of a finite element numerical study on seismic soil–structure interaction representative of an experimental setup from the past. The results show how high-frequency motion generated in soil in the steady-state response, apparently representative of soil elastic waves, affects the steady-state response of a structure, that is, it is presented how the structure in the analysed case resonates with the soil elastic waves. The numerical findings are verified against the benchmark experimental example to indicate similar patterns in the dynamic response of the structure.
... where V, H, and M = vertical, horizontal, and rotational (moment) limiting loads, respectively. Gourvenec and Randolph (2003) performed analyses in the form of "swipe" tests, based on the side swipe loading paths introduced by Tan (1990) to generate the shape of the failure envelopes where a foundation was loaded to failure in one direction first, followed by loading in a second direction. Gourvenec and Randolph (2003) performed a swipe test in two steps. ...
Ring foundations are used to support tall and heavy circular onshore structures such as chimneys, cooling towers, storage tanks, and silos and offshore structures such as wind turbines and annular platforms. The present study focused on developing failure envelopes for ring foundations subjected to the combined loading of vertical (V), horizontal (H), and moment (M). Parametric three-dimensional finite-element limit analyses were carried out for circular and ring foundations resting on the surface of cohesive soil following the Tresca criteria. The failure envelopes were generated separately under V∶H, V∶M, and H∶M loading combinations. Variations in the ring foundation geometry (Ri/Ro) of 0.2, 0.4, 0.6, and 0.8 and linearly increasing soil heterogeneity values (kB/sum) of 0, 1, 2, 3, 6, and 10 were considered in this study. The results indicated variations in failure loci with a variation in Ri/Ro and kB/sum. The typical contours of failure loads under the combined loadings and three-dimensional failure surface patterns are presented for the ring foundations with Ri/Ro=0.2 and 0.8 to understand the shape of the failure surfaces.
... Therefore, a homogenous soil layer has been modelled numerically to be representative of Leighton Buzzard sand, fraction E of the following soil geotechnical properties: γ s = 2647 kg/m 3 , e min = 0.613, e max = 1.014, D 10 = 0.095, D 50 = 0.14 (Tan, 1990). The initial K 0 condition has been assumed to be equal to 0.5 as deemed appropriate for dry sand at low mean effective stresses (Stroud, 1971). ...
This work presents results of a finite element numerical study of a simple case of soil-structure interaction when excited by a harmonic driving force at base of soil. A simple structure with a foundation on piles embedded in dry sand is analyzed. An advanced soil constitutive model is used to model soil nonlinear behavior in a reliable way. The results of the numerical study reveal how high frequency motion is apparently generated within the soil in the steady state part of the dynamic response. Moreover, it is presented how this soil-released high frequency motion acts on a simple structure embedded in soil. The numerical results are presented in comparison with an example of benchmark experimental data from the past to reveal that similar patterns can be observed in the numerical and experimental results regarding the structural response. Finally, short discussion highlights the importance of these findings in earthquake engineering and points out the potential source of the high frequency motion.
... An alternative approach is to use failure envelopes or more frequently, with respect to granular materials under drained conditions, yield envelopes, pointing out that the stress dependency of shear strength for granular materials leads to gradual yield and hardening with increased displacement in this case (Randolph & Gouvernec, 2011). Early studies on the yield surface of shallow foundations in sand were based on data collected by single gravity (1g) experiments (Ticof 1978, Butterfield & Ticof 1979, Nova & Montrasio 1991, Georgiadis 1993, Gottardi & Butterfield 1993, Tan 1990, Dean et al. 1992, Martin 1994, Gottardi et al. 1999, whose results indicated that the yield surface of such kind of foundation can be described by a rotated parabolic ellipsoid in (Q, H, M) force space, that is a rotated ellipse in the (M, H) plane and a parabola in planes along the Q axis at constant M/H ratio. A number of works has then focused on the response of caissons foundation for offshore wind turbines to combined loads (Byrne & Houlsby 1999, Byrne & Houlsby 2001, Villalobos 2006, Villalobos et al. 2009, Achmus et al. 2013, Ahlinhan et al. 2019, Li et al. 2015, Zafeirakos & Gerolymos 2016. ...
... Analyses on the failure envelopes under combined loading conditions are carried out using sideswipe tests (Tan 1990) and fixed-ratio displacement-controlled probe tests (Supachawarote, Randolph, and Gourvenec 2004). The reference point (RP) is fixed at the bottom center of the foundation in Figure 1. ...
The bearing capacity of bucket foundations subjected to combined vertical-horizontal-moment loadings (V-H-M) is an important issue for its design and application. This paper investigates the response of bucket foundations under V-H-M loadings in silt-over-clay using small strain finite element method. Model validation is carried out by comparing with previously testing data with good agreement obtained. Then parametric study is conducted to study the effect of embedded ratio, soil property and top layer thickness. It is found that the soil failure mechanism and corresponding bearing capacity of bucket foundations in silt-over-clay are significantly different to that in clay only condition. Approximating expressions are proposed to describe the unique trends of the normalized failure envelopes for bucket foundations in silt-over-clay soil deposits. The findings of this study could help to guide design application of bucket foundations.
... The bearing capacity is characterized by a foundation load from the continuous load-settlement curve when it is no longer changed with the increase of the settlement. The detailed method of characterizing the bearing capacity is similar to Tan (1990). The Monte Carlo simulation is used to generate the soil profile realizations. ...
Geological heterogeneity is a result of the natural deposit process of strata with a highly irregular and uncertain distribution of soil mass in the real world. However, compared with the effect of inherent spatial variability of soil properties on geostructures, the effect of geological heterogeneity has received less attention so far. In view of this limitation, this paper adopts a Markov random field model to stochastically simulate the geological heterogeneity for assessing the bearing capacity of a shallow foundation with quantified uncertainty. By mapping the generated stratigraphic realizations in the commercial software FLAC3D version 7.0, an ensemble of numerical models is generated. Computational results show that geological heterogeneity has a significant influence on the estimated capacities. Information entropy is used to characterize the geological uncertainty. It is not surprising that the increase of boreholes could reduce the average information entropy, and thus reduce the standard deviation of bearing capacities. But the effect of increasing the borehole numbers on the uncertainty reduction exhibits a clear nonlinear form with a potential to select an optimal borehole number. Results from the proposed stochastic analysis provide a range of calculated capacities, which can be used to mitigate the risk of insufficient bearing capacity.
... e loading methods of displacement-controlled swipe tests and fixed displacement ratio probe tests are commonly used for establishing the failure envelope of combined loading. e displacement-controlled swipe test was first proposed in [23] and consists of two main steps, as illustrated in Figure 4, which have been widely employed to numerically investigate the bearing capability of the foundation [24][25][26]. First, a given displacement u i is applied to the foundation along a certain direction starting from zero until the ultimate bearing capacity is reached. ...
The composite bucket foundation of offshore wind turbines is subjected to a variety of loads in the marine environment, such as horizontal load H, vertical load V, bending moment M, and torque T. In addition, due to the characteristics of its connection section, the water flow around the foundation will produce scour pits of various degrees, reducing the depth of the bucket foundation, which has a nonnegligible impact on the overall stability of the bucket foundation. In this paper, the failure envelope characteristics of different combinations of loads on bucket foundations, including V-H-T, V-M-T, conventional V-H-M, and noncoplanar V-H-M, are numerically investigated with considering different scour depths. The numerical results indicate that the V-H-T, V-M-T, conventional V-H-M, and noncongruent V-H-M failure envelopes gradually shrink inwards with increasing scour depth, and the stability of the composite bucket foundation decreases; the conventional V-H-M failure envelope shows an asymmetry of convexity to the right, and the noncongruent V-H-M failure envelope shows an asymmetry of outward convexity to the left and right. The corresponding mathematical expressions for the failure envelope are obtained through the normalized fitting process, which can be used to evaluate the stability of the bucket foundation based on the relative relationship between the failure envelope and the actual load conditions, which can provide practical guidance for engineering design.
... Previous studies (Supachawarote et al., 2005;Zou et al., 2018) show that the swipe-tests proposed by Tan (1990) may seriously underestimate the bearing capacities. Therefore, in this study the probe-tests are employed to determine the failure envelopes in the V-H, V-M and V-H-M spaces. ...
This paper carries out a numerical study to investigate the bearing capacities of caissons in stiff-over-soft clay under combined V–H-M loadings. A finite element model is generated and validated with available data in open literature, where a good agreement is obtained. A parametric study is then performed to explore the effects of the upper clay thickness, skirt length, the mobilization of vertical loading and different soil properties on the failure mechanism and corresponding bearing capacity of caissons in stiff-over-soft clay under combined V–H-M loads. The results show that the failure mechanisms of caissons in stiff-over-soft clay are significantly different from those in uniform clay; hence a dramatical distinction between the failure envelopes in stiff-over-soft clay and uniform clay can be found. Last but not the least, based on the numerical results, an empirical design approach is proposed to predict the failure envelopes of caissons under various loading situations.
... Recently, the analysis of offshore foundations such as spudcan and shallow foundations have used plasticity concepts to express the bearing capacity of foundations under combined vertical (V), horizontal (H) and moment (M) loading (Murff, 1994;Tan, 1990;Martin, 1994;Bransby and Randolph, 1998). ...
Finite element analysis of the fluke-soil interaction behaviour of drag anchors in undrained soil has allowed calculation of plastic yield loci for characterisation of fluke failure states. The yield loci produced are examined in terms of soil deformation mechanisms and kinematics and are incorporated into a novel method for drag anchor design.
... The ultimate vertical load bearing capacity (V ult ) of the pile is taken as the load corresponding to a settlement of 0.03D (Davisson, 1972, Ng et al., 2004. For combined loading, the swipe method proposed by Tan (1990) is used where a vertical load is applied to the pile head by stacking weights first, and then the currents and lateral load are applied. installed at 10D in front of the model pile, and the distribution of u c along water depth can be obtained by adjusting the height of the detector. ...
This paper presents the results of a series of laboratory studies to explore the effects of water flow on the bearing capacity of monopiles in sand. The load-displacement relationship, axial force, normalized bending moment of the pile shaft, the p–y curves and the bearing envelope are obtained to quantify the effect of water flow on the bearing capacity of the monopile. The results demonstrate that water flow can result in a maximum scouring depth of 0.7 D (pile diameter), which reduces the lateral bearing capacity by about 4–10%. It is also found that the bearing capacity of the pile for resisting eccentric lateral load (equals to moment and horizontal loads at mudline) slightly increases at the initial stage with the rise of the applied vertical load. Finally, the bearing capacity envelopes of pile with and without water flow are proposed, which can provide guidance for the design of monopiles.
... Recently, the analysis of offshore foundations such as spudcan and shallow foundations have used plasticity concepts to express the bearing capacity of foundations under combined vertical (V), horizontal (H) and moment (M) loading (Murff, 1994;Tan, 1990;Martin, 1994;Bransby and Randolph, 1998). ...
... This procedure was also repeated until the pilehead rotation suddenly increased. For combined loading, the tests were conducted under two loading sequences of V→T and T→V, and the swipe method (Tan, 1990) was used in this study. This is, applying constant magnitudes (about 33% and 66%) of ultimate V (or T) and keeping its loading direction unchanged, then conducting another load of T (or V) step by step. ...
Pile foundations may experience torsional loads induced by eccentric horizontal loads arising from wind, wave or ship collisions in offshore environment, in addition to axial loading from the supported superstructures. 1g model experiments were conducted in the laboratory to investigate the behaviour of single piles under independent vertical (V) and torsional load (T), and combined vertical-torsional (V-T) loads. Four types of layered soil profile of SC (sand-over-clay), CS (clay-over-sand), SCR (sand-over-clay-over-rock) and CSC (clay-over-sand-over-clay) were considered. The vertical load-displacement response, the torsion-rotation response, and the load transfer under two loading sequences (i.e., V→T and T→V) were observed. For the piles embedded in SC and CS, the bearing capacity envelopes in V-T plane and their simplified calculation formula were obtained as a design reference for engineers. The results indicate that the response of piles subjected to independent loading is substantially different from combined loading, and the soil profile and the load sequence have a significant effect on the bearing behaviour of piles. Compared with pure torsional pile, the ultimate torsional bearing capacity of the piles in SC under the combined V→T loading decreases by about 13-25%. However, the ultimate torsional bearing capacity of the piles in CS and SCR under the combined V→T loading increases by about 39-69% and 2%, respectively. In comparison to independent vertically loaded pile, the ultimate vertical bearing capacity of the piles in SC, CS and CSC under the combined T→V loading decreases by about 3% to 16%. This study shows that a complex interaction of vertical and torsional loads in various layered soils needs to be considered in a practical design.
... A fine-grained silica sand commonly known as Leighton Buzzard Fraction E sand was used for all tests, which has a typical average diameter D 50 of 0.14 mm and a specific gravity G s of 2.65. The sand has a maximum (e max ) and minimum (e min ) void ratio of 1.01 and 0.61, respectively, and a coefficient of uniformity C u of 1.58 (Tan, 1990). Details of the preparation methodologies for the FM tests can be found in the references provided in Table 1. ...
Predicting the impact of tunnelling-induced ground movements on existing foundation systems or infrastructure is an important stage during tunnel design or risk assessment processes. Centrifuge modelling has been used extensively as a tool to study soil movements caused by tunnelling and their interactions with existing structures. In 2D plane-strain centrifuge models, tunnel volume loss can be simulated in a variety of ways, but is conventionally done using a fluid-filled flexible membrane or a rigid boundary mechanical model tunnel. The choice of model tunnel has an impact on the imparted tunnel boundary displacements and resulting ground deformations , yet a thorough quantitative evaluation of these effects has not been conducted. This paper aims to address this by contrasting plane-strain centrifuge test results from experiments using a flexible membrane model tunnel with those from a newly developed eccentric rigid boundary mechanical model tunnel. A quantitative assessment of surface and subsurface settlement trough characteristics as well as soil shear and volu-metric response is provided. Results from numerical analyses using a hypoplastic constitutive model are also included, focusing on evaluating centrifuge spin-up effects and contrasting numerical outcomes with experimental data relating to settlement trough characteristics and soil shear/volumetric response. The outcomes of this paper should benefit future researchers considering which type of model tunnel to adopt when developing centrifuge tests related to 2D plane-strain tunnel modelling.
... For the case of soil relative density D r ¼ 50%, the critical buckling load decreases faster as the pier height increases compared to the cases of D r ¼ 30% and D r ¼ 40%. This is because the sand with a relative density of 50% can offer more lateral support to the pile for the unit length than that of Dr ¼ 30% and Dr ¼ 40% (Table 4) [22,28]. Therefore, for the case of Dr ¼ 50%, as the pier height increases, the length of pile embedded in the soil decreases, and the lateral support to the pile decreases rapidly, which leads to a rapid decline of the critical buckling load of pile. ...
Buckling instability has been recently identified as a possible mechanism of pile failure in liquefiable deposits and this failure mechanism is not explicitly mentioned in most design codes. To carry out routine design and checking, it is necessary to reliably estimate the critical buckling load of pile for a given liquefiable site. However, the existing calculation methods for the critical buckling load of pile in liquefied soils do not consider the influence of geometric imperfections and nonlinear behavior of the pile. In this paper, an efficient approach using the Beam on Nonlinear Winkler Foundation (BNWF) model is proposed to calculate the critical buckling load of pile in liquefied soils considering geometric imperfections and nonlinear behavior of the pile. The method is verified and validated using the finite element method and results from centrifuge tests. Furthermore, parametric analysis has been carried out to understand the influence of buckling load for different soil relative density, initial geometric imperfections of pile, flexural rigidity of pile, and pier height. It is found that the critical buckling load of pile in liquefied soils increases with the increase of soil relative density and flexural rigidity of pile, and decreases with the increase of initial geometric imperfections of pile and pier height. Finally, a simplified estimation method based on Euler buckling theory is provided for predicting critical buckling load of pile in liquefied soils and an example is taken to show the application.
... The majority of studies on the effect of multidirectional loading are focused on pile foundations and the development of Winkler-type models (e.g. [17,19,24]), where the pile-soil interaction mechanisms away from the soil surface along the pile may be quite different to those occurring during loading of a low aspect ratio caisson foundation or anchor. This paper focuses on the capacities of a caisson in drained medium dense sand under multidirectional loading. ...
This paper presents centrifuge tests undertaken to investigate the combined VH capacities of suction caisson in sand under multidirectional loadings following series of low magnitude horizontal cyclic loading. These loading paths are relevant to foundations of array of floating renewables such as wave energy converters or wind turbines. The centrifuge tests mainly provide information about the V–H yield envelopes in different loading directions and the Hx–Hy yield envelopes in the horizontal plane so that the effect of multidirectional loading can be analysed. The evolution of the yield envelope after cyclic loadings is first presented. Yield envelopes for load change angle β of 60°, 90°, 120° from the initial horizontal cyclic loading direction are then presented, and the mechanisms for increased capacity for β > 90° and reduced capacity for β < 90° are discussed.
... The behavior of piles and caissons subject to combined loading has been widely studied by a number of authors (Tan 1990;Murff 1994;Houlsby and Martin 1992;Bransby and Randolph 1998;Mayne et al. 1995). Plasticity methods have been used to formulate yield loci for combined loading response. ...
Geotechnical centrifuge tests were conducted to examine the behavior of low-aspect-ratio piles and caissons in clayey soils subject to high moment loading. Model piles with an aspect ratio of two were tested in the 150g-t centrifuge at Rensselaer Polytechnic Institute. Results include moment-inclination and force-displacement response for different loading conditions. Numerical studies were also performed consisting of three-dimensional finite-element simulations in order to predict capacities. The comparisons are performed in terms of the total resistance exerted by the soil on the caisson. This paper focuses on presenting the ultimate bearing capacity factors, including both experimental and numerical results. In addition, results are compared to a series of studies available in the literature, which include upper-bound solutions and experimental results.
... In a swipe test the pipe embedment is kept constant during lateral displacement-controlled motion of the pipe. According to plasticity theory of foundation behaviour, for small displacements applied sufficiently rapidly that dissipation of excess pore-water pressure is not allowed, the load path in a swipe test will follow the relevant undrained VeH yield envelope, ignoring minor elastic adjustments [17,18]. Fig. 4 illustrates schematically the behaviour that is expected to be encountered in a large-displacement swipe test. ...
The soil resistance developed during temperature- and pressure-induced large lateral movements of shallowly embedded subsea flowlines is an important input parameter for the structural design process. A major source of uncertainty in calculation of the soil resistance is the undrained shear strength of the soil berm produced as the flowline moves across the seabed, which is affected by the level of remoulding. To investigate the effect of pipeline embedment and displacement amplitude on the shear strength of the berm, a set of centrifuge model tests was conducted on kaolin clay, involving laterally moving pipelines with constant embedments in the range 5%–35% of the pipe diameter. Back-analysis of the test results, using finite element limit analysis, showed that the shear strength of the soil berm is a function of pipe displacement amplitude, pipe embedment, and soil sensitivity. On the basis of these results, we propose that the overall berm undrained shear strength may be determined as a convolution of the shear strengths of its constituent soil elements. Finally, a formula is presented for calculating the shear strength of soil elements within the soil berm, and this is used to back-analyse the overall soil berm resistance from the model tests.
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... The foundation has a diameter of 30 m, a height of 12 m and with bulkheads. The combined loading methods include the swipe loading method [29,30] and the fixed displacement ratio method [31]. The swipe method can directly search the general shape of the envelope of bearing capacity of foundation in load space, which is simple and fast. ...
The composite bucket foundation for offshore wind turbine bears the vertical load from not only the superstructure and the horizontal load, caused by wind and wave, but also from the torque load caused by rotating structures, such as blades. Based on layered soil foundation, the influence of the skirt height, the friction coefficient between soil and bucket foundation and the diameter of the bucket foundation on the stress of the bucket skirt under the torque load are studied in this paper. Moreover, the envelope curves of the bearing capacity of H–T and V–H–T are obtained by the fixed displacement ratio loading method. The bearing capacity characteristics of composite bucket foundation under different loading combinations are analyzed. The results show that: (1) The effect of inside soil on the bucket skirt is greater than that of the outside soil; (2) when composite loads are applied, the torque-bearing capacity decreases slowly with the increase of horizontal force, and when the horizontal force increases to a certain value, the value of the torque decreases significantly; and (3) the shape of the H–T failure envelope of the bucket foundation has no obvious change, vertical load have less effect on horizontal and torque load.
... 2. It controls the position of the parallel point, defined by Tan (1990), which is the peak of the potential surface. For v less than unity, the parallel point is moved to a lower value of / peak VV . ...
This PhD thesis deals with the response of caisson foundations in sand for offshore wind turbines submitted to combined monotonic and cyclic loadings. First, the failure process and failure envelope (or bearing capacity diagram) of a caisson foundation in sand under combined monotonic loadings is investigated using the conventional Mohr-Coulomb constitutive model. A Combined Lagrangian-Smoothed Particle Hydrodynamics(CLSPH) method is adopted to consider large deformations and the limitations of the approach are highlighted. A recently developed critical state model for sand (SIMSAND) is then introduced and combined with the CLSPH method. Rectangular channel soil collapse tests and granular column collapse tests considering different aspect ratios are simulated to validate the approach in terms of final deposit morphologies, flow profiles and undisturbed areas.The CLSPH method and the SIMSAND model are then used to investigate the bearing capacity diagram of the caisson foundation in sand. Different parameters affecting the shape and size of the failure envelope are considered, as soil density and stiffness, friction strength, grain breakage, geometry and aspect ratio of the foundation. An analytical formula is introduced to describe the 3D failure surface reproducing the numerical results. Based on the proposed analytical formula, a macro-element for the caisson foundation in sand submitted to monotonic and cyclic loadings is finally developed within the framework of hypoplasticity. Validation is provided through comparison with experimental results.
... There are numerous advantages of this approach compared to classical bearing capacity methods (Terzaghi, 1943;Meyerhof, 1951;Vesić, 1973), as has been discussed extensively in previous work (e.g. Tan, 1990;Gottardi & Butterfield, 1993;Bransby & Randolph, 1998;Martin & Houlsby, 2000;. Failure envelopes can also be used to develop plasticity-based macro-element models for shallow foundations (e.g. ...
The failure envelope approach is widely used to assess the ultimate capacity of shallow foundations for combined loading, and to develop foundation macro-element models. Failure envelopes are typically determined by fitting appropriate functions to a set of discrete failure load data, determined either experimentally or numerically. However, current procedures to formulate failure envelopes tend to be ad hoc, and the resulting failure envelopes may not have the desirable features of being convex and well-behaved for the entire domain of interest. This paper describes a new systematic framework to determine failure envelopes – based on the use of sum of squares convex polynomials – that are guaranteed to be convex and well-behaved. The framework is demonstrated by applying it to three data sets for failure load combinations (vertical load, horizontal load and moment) for shallow foundations on clay. An example foundation macro-element model based on the proposed framework is also described.
... At present, researchers widely use the 'failure envelope' approach to study the bearing capacity of foundations under combined loading [1][2][3].The methods of determining the failure envelopes mainly include swipe test [4],fixedratio probe test and combined load-displacement searching method [5].Now, suitable methods for determining the V-H, V-M and H-M failure envelopes have been identified [6][7]. But in the field, foundations for offshore wind turbines are also subjected to the torsional load T. Most of researchers use complicated ways to determine the failure envelopes including torsion [8][9], and consider less about the interaction between the moment load M and the torsional load T of bucket foundations. ...
... Yield surfaces can be established either by swipe analyses (Tan 1990) or by probe analyses (Bransby and Randolph 1998). A swipe analyses allows the entirety of the yield surface to be tracked, although the tracked load path lies marginally inside the real yield envelope (Gourvenec and Randolph 2003). ...
Suction caissons have recently been considered as potential anchoring solutions for floating renewable devices (wind turbines and wave energy converters) in shallow waters, where-unlike for floating oil and gas applications in deep water-sandy seabeds are to be expected. This paper presents a simple framework to calculate the maximum drained capacity of a caisson under inclined loading in sand and the associated position of the padeye, as a function of the load inclination. The framework assumes critical-state conditions and is based on the establishment of yield envelopes in the horizontal and vertical loading space at the location of the padeye. The yield envelopes were established through numerical modeling and validated by centrifuge tests; they are described by a closed-form solution that enables the prediction of caisson capacity.
... Loads [2]. ...
This research note presents a numerical investigation into the bearing behavior of an embedded spud-can in normally consolidated soil. The numerical model is implemented with ABAQUS *TM. The different embedment depths from shallow to deep are considered in this research note. The numerical model is based upon the 'small strain finite element (SSFE)' approach to compute capacity of the installed spud-can. The numerical model allows a systematic estimation of the combined bearing capacity of the embedded spud-can at various depths. In the numerical model, the spud-can is considered as a rigid body. In the results, a normal consolidated clay profile and the soil are modeled as linearly elastic and perfectly plastic material. The bearing capacity factors for various embedment depths from shallow to deep for VHM loading for the spud-can foundation of a jack-up rig are presented. The results are also compared with other available results from the literature.
... Note: * after Lee [3]. † after Tan [4]. ...
Size effects in miniature cone penetration tests (CPTs) are examined by performing a series of 1 g laboratory tests using three penetrometers of 3, 6, and 12 mm in diameter (D) in two grades of dry Leighton Buzzard sand respectively. It is found that the size effects primarily depend on three non-dimensional geometrical parameters, including relative penetration depth (H/D), normalised surface roughness of the cone (Ra/d50), and normalized cone size (D/d50). Test results showed that: (1) H/D is a major size factor influencing the cone resistance at relatively shallow depths, and its influence may disappear while the localized failure mechanism dominates. (2) the cone resistance may increase with a decreasing value of D/d50 in some circumstances, and this effect attenuates in loose sand; (3) the cone resistance is positively related to Ra/d50, especially for cones with an intermediate rough interface. These size dependent behaviour is attributed to the dependency of the failure pattern and sand properties on the stress level, strain level, and non-local interactions of underlying microstructures and the dependency of the shearing resistance of sand-cone interface on Ra/d50.
The offshore wind industry is experiencing rapid growth worldwide, serving as an effective solution to counteract climate change induced by global warming. A fundamental component of this industry is offshore wind turbines, which play a pivotal role in converting wind energy into electricity, contributing to sustainable and clean energy. Today, modern foundations, such as suction caissons, play a very prominent role in reducing cost and installation time for offshore wind turbines. This article focuses on the bearing capacity analysis of caisson foundations utilized in offshore wind turbines situated in sandy soils under combined loading conditions. Additionally, the development of failure envelopes for these foundations is addressed. For this purpose, a novel numerical approach known as the "sequential swipe test" is employed to develop the failure envelopes. This method has been less commonly used in sandy soils so far. The failure envelopes are derived using a three-dimensional explicit elasto-plastic finite element method, taking into account the soil-foundation interaction. Then, the effects of dimensions and embedment ratios of the caisson foundations are investigated on the failure envelopes. The results reveal that as the embedment ratio increases from 0.5 to 1 and subsequently to 2, the normalized horizontal bearing capacity increases by 1.8 and 2.7 times, respectively. Similarly, for the normalized rotational bearing capacity, these values increase to 2 and 3.1, respectively. Afterward, analytical relationships for the development of failure envelopes are presented, offering accurate predictions of the bearing capacity of suction caisson foundations under combined loading conditions. Eventually, simplified algebraic expressions are proposed to enhance the efficiency and applicability of the introduced relationships in engineering problems and practical scenarios. These expressions quantify the parameters based on the embedment ratios of the caisson foundations, ranging from 0.5 to 2.
This paper is concerned with the V-H-M failure envelopes for conical foundations under combined loadings on anisotropic clay. The study employs the three-dimensional finite element limit analysis (3D FELA) technique and utilizes the well-established Anisotropic Undrained Shear (AUS) failure criteria. The focus of the study is on evaluating the influences of the cone apex angle (β) and the anisotropic factor (re) on the bearing capacity of conical foundations subjected to external forces of vertical force (V), horizontal force (H), and moment (M). The combinations of V-H, V-M, and H-M load spaces are analyzed using dimensionless output parameters (V/suTCA, H/suTCA, M/suTCAD), and the various characteristics of failure mechanisms of the conical foundation are examined. Alongside FELA, the study introduces an innovative machine learning approach using Categorical Boosting (CATBoost), Extreme Gradient Boosting (XGBoost), and Gradient Boosting Machine (GBM) to evaluate the correlation between input parameters and their outcomes. The proposed machine learning models are rigorously verified and validated with the CATBoost model, showing exceptional agreement with numerical results, as demonstrated by an impressive R2 value of 99.99 %. The present study is a practical and efficient method for evaluating the 3D failure envelope of conical foundations on anisotropic clay under general loading conditions in (V-H-M) space.
This study numerically investigates the undrained bearing capacity of circular foundations founded on a two-layered clay under combined loading of vertical, horizontal, and moment loads using three-dimensional finite-element analysis. Each clay layer has different thicknesses and shear strengths, and two types of foundation–subsoil interface are considered: an interface with (a) zero tensile capacity or (b) nonzero tensile capacity. Analysis results are presented in the form of normalized failure envelopes for a wide range of layer thicknesses and shear strength ratios. The presented normalized failure envelopes under combined loads with or without the interface tension can be considered as graphical solutions for circular foundations on a two-layered clay in offshore marine environments. Failure mechanisms under various combined loads provide further insights into foundation-layered soil interactions.
2017 Elsevier Ltd The assessment of potential for building damage due to ground displacements caused by tunnelling is a global issue being faced by engineers. There is a two-way interaction between tunnelling and existing buildings; tunnel construction affects a building by inducing displacements in the soil underlying its foundation, and buildings influence tunnelling induced displacements via their weight and stiffness. Numerical analyses are widely used to investigate tunnelling and its impact on structures, however numerically predicted ground displacements are generally wider and shallower than those observed in practice. This paper presents a two-stage mixed empirical-numerical technique to estimate the effect of building stiffness on ground displacements due to tunnelling. In the first stage, greenfield soil displacements are applied to the soil model and the nodal reaction forces are recorded. In the second stage, the effect of tunnelling on a structure is evaluated by applying the recorded nodal reactions to an undeformed mesh. Results from conventional numerical analyses of the problem are compared against those obtained using the mixed empirical-numerical approach. Results demonstrate the importance of imposing realistic inputs of greenfield displacements when evaluating structural response to tunnelling.
Combined piled raft foundation (CPRF) is an effective solution for supporting high-rise constructions. The traditional design philosophy of CPRF does not consider the capacity of foundation based on combined vertical (V), horizontal (H), and moment (M) load. However, V-M-H load acts on the CPRF system concurrently due to the action of wind, wave, earth pressure, and earthquake loading in addition to gravity loading. In this context, the present investigation deals with the effect of combined V-M-H load interaction on the behavior of CPRF in sand and clay, respectively. The response of CPRF under combined loading is obtained using a 3D finite element analysis. First, validation of the numerical model is performed considering the model test results conducted in Agartala sand and another based on the available field test result of Messeturm Tower in Frankfurt clay obtained from the literature. Further, failure and design envelopes for the validated CPRF system are developed considering V-M-H load in both sand and clay deposits attributing a variety of influential system parameters. Simplified expressions for design lateral and moment capacities are proposed based on multiple linear regression analysis. Finally, the implication in design based on the findings of the present study is illustrated using a prototype case study structure.
Gravity wharf (GW) structures are gaining popularity in new port constructions, as well as expanding existing ports. When such structures are located on saturated alluvial seabed, their seismic performance needs to be established, particularly from a liquefaction point of view. In this paper, time domain finite element (FE) analyses were carried out on a typical GW structure cross section located on a 10-m-thick saturated sand bed. In addition, the same cross section was tested in a geotechnical centrifuge and subjected to earthquake loading. The results from the FE analyses were directly compared with the centrifuge test data. Firstly, the settlement and rotation of the GW structure when subjected to a series of earthquake loadings were compared. It was shown that the FE analyses were able to capture the level of settlements quite accurately. Similarly, the dynamic responses of the GW structure observed during the centrifuge testing were compared with the results from the FE analyses. Finally, the excess pore pressures generated in the sand bed were compared with the experimental data. In addition to the centrifuge testing, the FE analysis was able to provide the spatial redistribution of the vertical effective stresses with the onset of excess pore pressure generation. Similarly, the excess pore pressure ratio contours could be constructed at any given time point. In combination, the results from the FE analyses and the centrifuge data concluded that the GW structures could perform well, even under strong earthquake loading with acceptable settlements.
The loading condition of bucket foundations for offshore wind turbines is very complicated and often under combined loading, but the torsion is always ignored. So, it is necessary to investigate the failure envelopes including torsion of bucket foundations. Under the premise of validating the reliability of the numerical model by comparing with other published data, failure envelopes in each loading space are obtained and the applicability of swipe test for the determination of H-T failure envelope and M-T failure envelope of bucket foundations is explored. The impacts of torsion and aspect ratio on the combined bearing capacities are studied. While revealing the law of impacts, equations are proposed to determine the respective failure envelopes and evaluate the combined bearing capacities. The V-H-M-T failure envelope can reveal the torsion effect on envelope under traditional V-H-M loading, the results show that the normalized V-H-M failure envelopes under different torsions almost coincide, torsion effect can be easily considered according to this characteristic.
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