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The reverse-consolidation caused by excavation inevitably affects the bearing capacity of basal soil to resist water pressure in confined aquifers, posing a risk to excavation stability. However, there is still a lack of efficient solutions to incorporate the layered heterogeneity into the analysis of the reverse-consolidation. This study proposes a practical approach where the spectral Galerkin method is used to capture the variation of soil properties with depth. The boundaries are characterized by time-dependent drainage boundary conditions to simulate the excavation process. The excess pore-water pressure profile is described by a single expression calculated by common matrix operations. The rationality and accuracy of the practical approach are verified by existing analytical models and field data. Subsequently, the permeability coefficient variability, relatively impervious interlayer, and sand interlayer are analyzed to illustrate their effects on the reverse-consolidation behavior of basal soil. Results indicate that the distribution of excess pore-water pressure is significantly influenced by the variability and distribution form of the permeability coefficient. The relatively impervious interlayer delays the dissipation of excess pore-water pressure and bears a large hydraulic gradient, while the sand interlayer is the opposite. These above influences become more significant as the excavation progresses due to the time effect. [ABSTRACT FROM AUTHOR]

This paper explores the effect of the sand cushion as a well-known remedial technique for foundations on reactive soils. Yet, instead of exploring the effect of the sand cushion on the soil and footing movements, this study contributes, for the first time, to reduce the slab foundation design thickness, using a specific depth of sand cushion, thus superseding the empirical approaches currently utilised in the estimation of the sand cushion thickness. To achieve this goal, an intensive parametric study was carried out on different slab dimensions, in different soil classes, and using different construction types, with the inclusion of 3 commonly used depths of the sand cushion. The study utilises a sophisticated three-dimensional (3D) hydro-mechanical finite element (FE) numerical model presented and validated by the authors in previous work (Shams et al., 2018). The same model was implemented in the parametric study of the current research in coupled flow-deformation and stress analyses with the presence of sand cushion. The results of the parametric study were used to generate design equations using the artificial intelligence technique. A computer program was developed for the design of stiffened slab foundations considering the effect of specific depth of sand cushion, which can be readily used by practitioners. [ABSTRACT FROM AUTHOR]

In this work, the three-dimensional failure mechanism of a deep soil-tunnel is established based on the nonlinear Mohr-Coulomb criterion and the upper bound theorem of the limit analysis subjected to the effects of pore water pressure. The formulas of the height, width and upper bound surface of a three-dimensional collapse of a deep soil-tunnel are derived from the three-dimensional failure mechanisms. The correctness and effectiveness of the proposed method is confirmed by comparing the results with those of existing studies. Then, the change rule of the geotechnical and geometrical parameters on the influence of the collapsing range and weight are studied. The results indicate that the pore water pressure has a significant influence on the range and weight of a tunnel collapse, but the initial cohesion determines the change rule of the pore pressure coefficient on the influence of the collapsing weight. The work in this study provides a reliable theoretical method for the optimization of the support designs of deep soil-tunnels. [ABSTRACT FROM AUTHOR]

We have developed a coupled hydro-mechanical model for the effect of plant roots on the mechanical and hydrological behaviour of soil (Świtała et al., 2018). This paper presents details on the implementation of the numerical model, considering the influence of plants on the strength and deformation of soil. The constitutive model is based on a Cam-clay model for unsaturated soils. The expansion of the yield surface is assumed to depend on both the soil suction and the reinforcement by plant roots. The constitutive model is implemented in a finite element code and its performance is demonstrated in a series of numerical examples. [ABSTRACT FROM AUTHOR]

This paper proposes a theoretical method to estimate the long-term time-dependent bearing characteristics of a driven pile. The viscoplastic behavior of the surrounding soils is described by nonstationary flow surface (NSFS) theory. The evolution of the soil behavior due to aging is incorporated in a skin friction softening model, which is used in the load-transfer method to predict the bearing capacity evolution of a driven pile. Extensive comparisons with experimental data are performed to illustrate the effectiveness and accuracy of the theoretical method. Both the proposed method and the experimental data show that the bearing capacity of the test piles increases by 30–50% due to the aging effect. The good agreement indicates that the long-term capacity evolution can be evaluated using the proposed method. [ABSTRACT FROM AUTHOR]

Floating offshore structures can be founded on submerged foundations such as anchor plates. Their extraction resistance is of major importance during and at the end of the lifetime cycle. During their lifetime cycle, the foundation is suspended to complex loading conditions due to waves, tidal currents and wind loads and its resistance has to be known. At the end of the lifetime cycle, the anchor plates have to be removed from the seabed. The extraction resistance of the anchors is thereby a lot higher than the sum of its self-weight and hydrostatic and earth pressure. When the anchor plate is moved, the volume underneath increases. This leads to a suction until inflowing pore water fills the newly created volume. In order to investigate this effect, an experimental study at model scale with a displacement-driven extraction is performed. Pore pressure measurements are carried out at various locations in the soil body and underneath the plate. The soil movement is tracked with the particle image velocimetry method (PIV). In the conducted experiments different extraction velocities are considered to investigate its effect on the extraction resistance. Numerical investigations with unresolved coupled CFD-DEM are carried out and validated against the experimental results. [ABSTRACT FROM AUTHOR]

Construction loads cause extra deformation and stress to nearby buried municipal pipelines. This paper investigates this issue by relating problems with inputs as free-field soil pressure or displacement by surface loading to the choice of an appropriate Winkler subgrade modulus for pipeline-soil interaction mechanisms. The theoretical analysis indicates that the input of surface load-induced soil pressures at the pipeline location results in much smaller moments and displacements of the pipeline. Although the Winkler solution using the Vesic spring modulus results in the same bending for a beam resting on the soil surface as that in elastic continuum when under a point load, its use is not always adequate for a buried pipeline with a finite embedment depth under external load and when subjected to free soil movements. An alternative expression for the spring modulus is given for a buried pipeline under a direct external load. The application of a passive Winkler modulus is proven rational when the pipeline is subjected to soil movement. A comparison between FEM analysis and the elastic continuum solution suggests that a displacement input or a coupled input be used for the analysis of a pipeline under surface loading, together with the application of a modified active Winkler modulus expression considering embedment depth and a passive Winkler modulus expression for surface loading–pipeline–soil systems under different input conditions. [ABSTRACT FROM AUTHOR]

Coupled Eulerian-Lagrangian (CEL) method is adopted to overcome the large mesh distortions near the footing corners under ultimate loading conditions. The reliability of the obtained bearing capacity factors N c and N q are assessed by comparing with the existing results. A modified expression of N γ is presented for a strip footing under uniform displacement considering both soil-footing roughness and internal friction angle of the soil. The failure patterns are investigated in terms of the displacement and velocity field beneath the footing. Moreover, the failure patterns are classified under different soil parameters and footing embedment. This study provides a new approach to the ultimate bearing capacity determination and failure pattern classification of strip footing resting on c - φ soils. [ABSTRACT FROM AUTHOR]

An advanced three-dimensional model is proposed to study the limit state of a tunnel face in spatially variable soils based on the upper bound theorem. The matrix decomposition method for generating the random field is further modified, allowing the soil spatial variability to be accurately captured with less computational effort. Verification exercises are carried out to demonstrate the satisfactory behaviour yielded by the proposed model in comparison with the random numerical method when tunnels are constructed in homogeneous and layered heterogeneous soils. Sensitivity studies are further performed via Monte Carlo simulations, illustrating the important effects of the spatial variability of the shear strength. [ABSTRACT FROM AUTHOR]

Abstract This paper investigates the effects of the footing loading position and the footing radii ratio (r i / r o) on the normalized bearing capacity. Both smooth and rough footings located on frictional and cohesive soils are evaluated by finite element limit analysis (FELA). Quadruple tests (i.e., T 1 , T 2 , T 3 and T 4) are propounded to reach the main goal in this study. The obtained results are presented in the form of normalized bearing capacity charts and the failure patterns for each condition. Based on the analysis, a nonlinear model is proposed to estimate the bearing capacity of a ring footing subjected to varying loading positions. [ABSTRACT FROM AUTHOR]

Abstract There are limited information on how an artificially non-liquefiable soil layer created by ground improvement beneath shallow foundations can help the reduction of liquefaction induced foundation settlements and the deterrence of bearing capacity failure effectively. This is addressed herein, numerically through a three-dimensional finite difference model using FLAC3D. The validity of the developed model was evaluated by comparing the results obtained from the model with the results of numerical studies and experimental centrifuge tests available in the literature. Using the validated model, the seismic response of a shallow foundation including bearing capacity and settlement was evaluated parametrically over a single DSM column in terms of its diameter and depth and also DSM group columns in terms of the diameter of columns and their center-to-center distance. Afterward, the influence of shallow foundation characteristic parameters was evaluated including thickness, width and embedded depth on the seismic response of shallow foundations over liquefiable soils improved by DSM columns. The obtained results can be used in practical engineering applications and provide new insight into the seismic performance of shallow foundations with DSM columns located over liquefiable soils. [ABSTRACT FROM AUTHOR]

Abstract The finite element implementation of a fully coupled hydro-mechanical constitutive model Zhou et al. (2012a, b) is presented here. An explicit integration scheme with four main steps is adopted to integrate the constitutive relation coupling with the soil water retention model. The finite element program can simulate complex hydro-mechanical processes with highlights on flow-deformation coupling and hydraulic hysteresis. The performance of the developed program is validated at both element level (against unsaturated triaxial test results) and small-scale model set-up level (against 1-d consolidation, sand column and loading/wetting test results). Several applications for unsaturated soils are analysed, including: (1) equilibrium processes after fast-drying/wetting (1-d); (2) slow-loading after different suction histories (1-d, compared with the finite element results by Sheng et al. (2003b); and (3) a flexible footing (2-d) affected by a leaking underground pipe. [ABSTRACT FROM AUTHOR]

Abstract The objective of this paper is to investigate the bearing capacity of spatially varying soil in the presence of non-stationary feature of undrained shear strength. Firstly, undrained shear strength is modeled by a non-stationary random field. In this model, the mean of undrained shear strength is non-zero at the ground surface and linearly increases with depth, while the coefficient of variation (COV) of undrained shear strength keeps constant. Based on this non-stationarity, an algorithm is proposed to produce the corresponding random field. Then, Monte Carlo Simulations are carried out to evaluate the statistical characteristics of the resulted bearing capacity, followed by a detailed discussion on the effects of COV, strength gradient parameter, distribution type, and vertical autocorrelation length. At last, two computation schemes that enable the prediction of statistical characteristics (e.g., mean, standard deviation, and cumulative probability function) of bearing capacity in non-stationary random fields utilizing results from a stationary one are proposed, and demonstrated through numerical examples. [ABSTRACT FROM AUTHOR]

Abstract In this paper, the bearing capacity and the failure mechanism of obliquely loaded footings on sand overlying clay are determined by using discontinuity layout optimization (DLO) procedure. The solution is illustrated as a set of design charts with the use of dimensionless parameters. Parametric studies are performed to show that soil properties, geometric parameters, and load inclinations are all related to the bearing capacity and failure pattern. A simplified model is developed based on artificial data generated through DLO. Validations are carried out to demonstrate the accuracy of the developed model. [ABSTRACT FROM AUTHOR]

Lunar environment features a low gravity field and ultra-high vacuum which shows significant effects on the bearing behavior of lunar soil ground for future lunar habitation. Therefore, the 2D Discrete Element Method was employed to simulate the plate load tests under different gravity fields in non-vacuum (i.e., excluding the van der Waals force) and high-vacuum (i.e., including the van der Waals force) environments, analyzing the bearing behavior and soil response under extraterrestrial environmental effects. The results show that a bilinear line bounded by 1g can be employed to describe the gravity effect on the gravity factors for ultimate bearing capacity and coefficient of subgrade reaction. The slopes are different in low and high-gravity fields, indicating that the high-gravity effect in a centrifuge cannot be directly applied to predict the bearing behavior of lunar soil ground in a low-gravity field. The affected area becomes deeper in depth and narrower in width with the decreasing gravity level in non-vacuum environment, while the affected area becomes deeper in depth and wider in width with the decreasing gravity level in high-vacuum environment. Such observations can provide advice for developing analytical models for the bearing capacity of lunar soil ground considering the extraterrestrial environmental effects. [ABSTRACT FROM AUTHOR]

In engineering practice, horizontal layers of reinforcement geosynthetics are widely used to improve the bearing capacity of foundations. However, there are few studies on the seismic bearing capacity of foundations on reinforced soil, and there is a lack of derivation of theoretical formulas in this direction. In this paper, based on the upper bound theorem of limit analysis, the seismic bearing capacity of foundations on reinforced soil is studied for the first time using the modified pseudo-dynamic approach. Seismic forces are calculated using a slicing method that adapts to spatial and temporal variations. Based on three different failure mechanisms, three different formulas and constraints are used. Each formula contains 61 variables, and the bearing capacity value is optimized by MATLAB program. By comparing the calculation results of three failure mechanisms, the exact upper bound solution of seismic bearing capacity for sliding failure is obtained. Considering the temporal as well as spatial characteristics of seismic forces, the effects of the coefficient of seismic acceleration, the internal friction angle, the damping ratio, the normalized frequency, and the reinforcement burial depth on the seismic bearing capacity are analyzed, providing a theoretical basis for the application of reinforced soil foundations in engineering practice. [ABSTRACT FROM AUTHOR]

Abstract The total-displacement loading EMSD (T-EMSD) method is applied in analyzing the undrained bearing capacity of strip footing near clay slope with linearly increased strength. According to the continuous field based upper-bound solutions obtained by the T-EMSD method, the consideration of strength gradient weakens the influence of strength ratio and slope height on the bearing capacity result. Investigation on corresponding velocity fields reveals that with the increase of the strength gradient the mobilized mechanism tends to contract around the foundation edge, thereby weakening the effect of the slope. Design equations are proposed based on the continuous field based upper-bound solutions. For subgrade with significant strength gradient, bearing capacity calculation with representative strength might lead to unacceptable overestimation and the present equation should be used in such case. [ABSTRACT FROM AUTHOR]

This paper presents numerical applications of a non-coaxial soil model, in which an anisotropic yield criterion is incorporated, to analyze two-dimensional strip-footing problems. Semi-analytical solutions of the bearing capacity for a strip footing that rests on anisotropic, weightless, cohesive-frictional soils are developed based on the slip line method. The degrees of influences of soil anisotropy and non-coaxiality on the bearing capacity of the strip footing are examined. From the viewpoint of strength and stiffness, it is necessary to incorporate both the strength anisotropy and non-coaxiality into numerical simulations and practical designs of geotechnical problems. [ABSTRACT FROM AUTHOR]

A numerical investigation of the ultimate pile capacity ( Q ult ) and failure behavior of T-shape deep cement mixing (TDM) piles is conducted under equivalent volume. Physical model tests are conducted to verify the numerical findings. The results reveal that both the shape of the enlarged pile cap and pile strength play key roles. Sensitivity analyses indicate that the effects of cap shape and pile strength on the complex load carrying behavior of TDM piles are attributable to changes in failure mode, which depend on the mobilized skin friction and bearing of both the cap and pile body. [ABSTRACT FROM AUTHOR]

Finite element limit analysis (FELA) is used to study the undrained bearing capacity of strip footing above voids in two-layered clays. Based on the FELA results, design charts and equations are provided to calculate the undrained bearing capacity factor N s . The impact of parameters on N s also has been investigated, including undrained shear stress ratio of the soil, thickness of the top layer, location, size, width, height and spacing of the voids. The failure mechanisms for a single void maybe classified into three categories: roof failure, combined roof and wall failure, bearing failure without void failure. [ABSTRACT FROM AUTHOR]

The complex soil-structure interaction factors to estimate load bearing capacity of a combined pile-raft foundation (CPRF) is scarce. A new prediction method is proposed to estimate both Ultimate Limit State (ULS) and Serviceability Limit State (SLS) bearing capacity of CPRF by evaluating the pile-raft and raft-pile interaction factors. The developed model is validated with available experimental results. The simplified expressions for the evaluation of load-sharing ratio and a mobilized factor of safety of CPRF considering the serviceability requirement of the structure are also proposed. It provides a simple design solution for CPRF subjected to vertical loading condition. [ABSTRACT FROM AUTHOR]

This study evaluates the bearing capacity and failure mechanism of strip footings placed on the top of slopes. A set of design charts containing the detailed critical failure mechanism information is presented for engineering practice. The results show that six distinct failure modes can be attributed to the bearing capacity of footings or to the slope stability issues based on the contribution of the soil self-weight. The occurrence of toe failure (S) is the threshold between the two geotechnical issues. The analytical solution based on the face failure mode is a conservative solution for bearing capacity issue. [ABSTRACT FROM AUTHOR]

Analytical and numerical solutions of the undrained load-carrying capacity of shallow foundations are mainly available for single foundations. This paper investigates the undrained limit states of two-spaced rectangular foundations with rigid connections. Three-dimensional finite-element analyses are carried out to systematically examine the coupled interaction of foundation spacing and degree of soil strength heterogeneity on the load-carrying capacity of the foundation systems under general loading. Results are presented in the form of ultimate limit states under pure vertical (V), horizontal (H), and moment (M) loads, and the failure envelopes under combined V-H, V-M, H-M and V-H-M loading. Soil failure mechanisms obtained from the finite-element analyses are shown for the representative loading paths of the two-foundation systems. Based on the failure mechanisms, the methods are established for calculating the undrained load-carrying capacity of the two-foundation systems to assist the foundation design in practice. [ABSTRACT FROM AUTHOR]

A cyclic-softening macro element model that represents mono-bucket foundation supporting offshore wind turbines in clay is presented in this paper. The model is formulated based on multi-surface plasticity with kinematic and isotropic hardening rule. The softening behaviour of the foundation subjected to a cyclic load sequence is captured real-timely in the macro element model through the contraction of yield surfaces. The model parameters are calibrated by uniaxial quasi-static load–displacement curves, which are obtained by finite element analyses with the cyclic behaviour of soil simulated via the cyclic contour diagram approach. The performance of the macro element model in representing the softening of a bucket foundation during a cyclic load sequence is demonstrated by comparing with parallel finite element analyses. A reasonable agreement has been achieved. The procedure to apply the model is suggested, considering different working scenarios with various cyclic to average load ratios. The macro element model developed is capable of capturing the real-time displacement of foundation in a load sequence, with high computational efficiency and accuracy. [ABSTRACT FROM AUTHOR]

Natural clay setup significantly contributes to the improvement of the bearing performance of a jacked pile. This paper presents a semianalytical solution to predict the time-dependent bearing capacity of a single pile in natural clays. The proposed solution properly incorporates the initial structure and stress-induced structure degradation of soils and the subsequent thixotropic and reconsolidation of disturbed soils. Pile penetration is simulated using the cavity expansion method (CEM) based on the Modified Structured Cam Clay (MSCC) model. The governing equations computing stress components during consolidation are established using a variable relaxation gradient function and are numerically solved by combining initial boundary conditions. A functional relationship between the ultimate strength and stress state of soils is presented according to critical state soil mechanics theory. The predicted results are validated against the results from the existing analytical approach, published centrifuge model tests, and laboratory model tests in structured clays. The excellent agreement between the measured and predicted values demonstrates that the method can properly predict the time-dependent bearing capacity of jacked piles in structured clays. Considering the impact of soil structure on soil setup plays a significant role in quantitatively evaluating the time-dependent bearing capacity of piles in natural clays. [ABSTRACT FROM AUTHOR]

The nonlinear compressibility and permeability of soft soils is a key factor in the consolidation of both composite and natural foundations. However, there are few corresponding consolidation theories for vertical drain-stone column composite foundations in which the nonlinear consolidation characteristics of soils can be taken into account. In this study, a nonlinear consolidation model is established to describe the seepage relations between soft soils, vertical drains and stone columns. Then, a consolidation governing equation is derived, where the total excess pore water pressure (EPWP), u ¯ , is a variable, and the average consolidation degree defined by strain and stress of the composite foundation is obtained, respectively. Numerous calculations are performed to analyze the consolidation behaviors of such composite foundations. The results show that the installation of vertical drains can enhance the consolidation rate effectively; the external load and the initial modulus ratio of column to soil have an influence on the stress concentration effect of stone columns. Finally, the proposed analytical solution is applied to the settlement calculation for an actual project, and the calculated results are in good agreement with the measured data in the early and late stages of consolidation. [ABSTRACT FROM AUTHOR]

This paper investigates the response of a circular shallow foundation constructed above a reinforced granular fill over clay deposit containing continuous square void. The numerical computations have been carried out employing a Finite Difference-Discrete Element (FDM-DEM) hybrid method. In the numerical simulations, the influences of the geometry and position of a square void with different dimensions and positions on the ultimate bearing capacity of the overlying shallow foundation, its load–displacement response, geogrid response and also the contact force network (CFN) underneath the footing have been rigorously examined. Moreover, the effects of the undrained shear strength of the underlying natural clayey deposit and the intervening geogrid stiffness on the behavior of surface footing have been evaluated. Results indicate that the bearing capacity of footing decreases by an increase in the width of the void while increasing the horizontal and vertical distances of void from the centerline of the surface footing suppresses its adverse effect. The negative impact of void on the bearing capacity of surface footing declines as the undrained shear strength of underlying clayey deposit increases. On the other hand, using a geogrid layer with higher stiffness leads to an increase in the ultimate bearing capacity of the overlying footing. [ABSTRACT FROM AUTHOR]

Meta-materials are engineered composites with physical properties that can introduce frequency band gap regions suitable for wave manipulation and filtering. This study investigates the seismic behavior of soil–structure systems with a meta-foundation designed using alternatively repeated layers of concrete and rubber. First, the frequency band gaps of the meta-foundation were derived using the Floquet-Bloch theory. The frequency band gaps for different meta-foundation configurations with infinite and finite numbers of unit cells were presented. Then, a two-dimensional (2D) plane-strain finite element simulation was proposed to study the isolation performance of meta-foundations on or embedded in soil half-space. Finally, two four-story steel structures with different dynamic characteristics were modeled under different input motions. The results show that direct embedment of meta-foundations in soil may break periodicity, requiring special treatments on the side boundaries of the foundation. Moreover, the numerical results show considerably enhanced structural performance for the meta-foundation system with a reduction up to 95.1% and 97.9% for the maximum horizontal acceleration and inter-story drift, respectively, compared to the non-isolated system. The results also indicate enhanced soil response under the meta-foundation and acceptable structural performance outside the band gap frequencies compared to the non-isolated system. [ABSTRACT FROM AUTHOR]

Monopiles are one of the major types of foundation systems for offshore wind turbines. To obtain the responses of large-diameter monopiles under lateral loading, a four–spring beam model is proposed based on the Timoshenko beam theory, which considers lateral soil resistance, pile shaft resistance, base horizontal force, and base moment. All the soil resistance components are represented by a series of distributed and concentrated springs deployed along the pile shaft and at the pile tip, respectively. The solutions for the internal forces and deformations are derived using the state space method for the nonlinear pile–soil interaction and then validated by recent field pile tests and numerical simulations. Furthermore, a parametric study is undertaken to examine the influences of pile diameter, embedded length, wall thickness, lateral load and soil stiffness on the pile responses. The results show that increasing the pile diameter and lateral load or decreasing the pile embedded length causes the pile deformation pattern to transform from a relatively flexible bending mode to a rigid rotational mode. Moreover, increasing the pile diameter reduces the pile deformations, and the distributed moment, base horizontal force, and base moment may have more significant contributions on the lateral bearing capacity of the monopile. [ABSTRACT FROM AUTHOR]

If no regularisation method is used during finite element modelling of strain-softening (brittle) materials, results become mesh dependent: manifesting as very thin shear bands whose thickness and orientation depends on the mesh discretisation. The objectives of this paper were to determine if mesh independent results were achieved, and to track the evolving width of the shear band when considering naturally occurring properties of soft clays, including a rate dependent stress-strain-strength relationship. The constitutive model included a destructuration process and strain-rate dependency, and the analyses allowed for local pore water flow. A bearing capacity problem was loaded to failure. Analyses were conducted with different mesh discretisation, loading rates and permeabilities. The results demonstrated mesh independent failure loads, and the strain-softening occurred in zones with thickness independent of mesh size. Local pore water flow delayed the initiation of strain softening and resulted in higher failure loads. The softening zones grew in thickness to over one meter, reinforcing that the finite element method is suitable for the determination of the bearing capacity of strain-softening sensitive clays. In conclusion, the rate dependent constitutive model is a promising method for regularising strain localisation in soft brittle clays under quasi-static loading conditions. [ABSTRACT FROM AUTHOR]

Bearing capacity of shallow strip foundations placed over both unreinforced and reinforced granular soils and subjected to combined loading is calculated by implementation of upper bound finite element limit analysis in conjunction with second-order cone programming technique. The soil mass is considered to be a granular medium reinforced with the inclusion of horizontal single and double layers of geogrid elements. To represent the impact of tensile resistance of reinforcement elements, an axillary variable is utilized to simulate the plastic energy dissipation of reinforcing elements without the application of any stress variables. General loading conditions are considered to profile the expansion of the failure envelopes in the V-H and V-M spaces for shallow strip foundations resting on reinforced soils. Results of this study are compared and validated against three different cases including the bearing capacity of shallow strip foundations subjected to vertical loading in the case of perfectly smooth and fully rough interfaces, limit load of shallow strip foundations subjected to combined loading, and vertical bearing capacity of shallow strip footings over a soil deposit reinforced with a single-layer of geosynthetic. Consistency of the results with those reported in the literature demonstrates the efficiency of proposed extended finite element upper bound formulations. The results are reported in the form of an efficiency factor which can be multiplied by the vertical bearing capacity of the shallow strip footing over unreinforced soil to find the ultimate bearing capacity of the reinforced foundation. The results show that the load inclination angle and eccentricity have significant impacts on the limit load and the optimum embedment depths of the reinforcement layer. It is further noted that the effect of reinforcement layer(s) in the improvement of bearing capacity in the V-M space is more pronounced than in the V-H space. The efficiency of reinforcement elements inclusion in improving the expanse of safe loading domain in the V-H and V-M spaces enhances with an increase in the soil internal friction angle. [ABSTRACT FROM AUTHOR]

This paper describes an international exercise aimed at assessing the geotechnical engineering profession’s ability to predict the response of shallow foundations on soft clay subjected to undrained loading. Predictions of bearing capacity varied by more than an order of magnitude and settlement by more than two orders of magnitude. Average and median predicted values deviated significantly from measured values. The results of this exercise highlight the need to develop tools to assist engineers to process site investigation data. The development of predictive models that connect directly to site investigation data is discussed. [ABSTRACT FROM AUTHOR]

Circular foundations are widely employed in offshore engineering to support facilities and are generally subjected to fully three-dimensional loading due to the harsh offshore environmental load and complex operational loads. The undrained capacity of surface circular foundations on soil with varying strength profiles and under fully three-dimensional loading is investigated and presented in the form of failure envelopes that obtained from finite element analyses. The combined ultimate limit state of circular foundations is defined as the two-dimensional failure envelopes in resultant H-M loading space accounting for the vertical load and torsion mobilisation. The effects of vertical load and torsion mobilisation, soil shear strength heterogeneity and loading angle from moment to horizontal load on the shape of normalised H-M failure envelopes are explored. A series of expressions are proposed to describe the shape of failure envelopes obtained numerically, enabling essentially instantaneous generation of failure envelopes and optimisation of a circular foundation design based on constraint of any input variable through implementation in an automated calculation tool. An example application is ultimately provided to illustrate how the proposed expressions may be used in practice. [ABSTRACT FROM AUTHOR]

This paper presents a study on the bearing capacity of eccentrically-loaded rough ring footings resting over cohesionless soil. To this aim, a series of 3D numerical simulations were performed using the finite difference method. In order to consider the effect of load eccentricity, reduction factor method is applied. In this method, the ratio of an eccentrically-loaded bearing capacity to the bearing capacity of the same footing under vertical load is defined. Comparison between the results of the numerical simulations with those of analytical solutions and experimental data indicates good agreement. A mathematical expression is also introduced for eccentrically-loaded ring footings. [ABSTRACT FROM AUTHOR]

In this research, the reliability analysis of seismic ultimate bearing capacity of strip footing is assessed with implementing slip lines method coupled with random field theory. The probability density functions of seismic and static bearing capacities which are log-normal and nearly normal distribution respectively are compared to each other. The predicted Probability Density Function (PDF) of the seismic bearing capacity by slip line method is verified, with those of the Terzaghi equation and Monte Carlo simulation (MCs). For uncertainties analysis by Terzaghi equation the N c , N q and N γ are assessed stochastically. [ABSTRACT FROM AUTHOR]

The stress characteristics method ( SCM ) has been used to compute the bearing capacity of smooth and rough ring foundations. Two different failure mechanisms for a smooth footing, and four different mechanisms for a rough footing have been considered. For a rough base, a curvilinear non-plastic wedge has been employed below the footing. The analysis incorporates the stress singularities at the inner as well as outer edges of the ring footing. Bearing capacity factors, N c , N q and N γ are presented as a function of soil internal friction angle (ϕ) and the ratio ( r i / r o ) of inner to outer radii of the footing. [ABSTRACT FROM AUTHOR]

Reliability analysis of bearing capacity of a strip footing at the crest of a simple slope with cohesive soil was carried out using the random finite element method (RFEM). Analyses showed that the coefficient of variation and the spatial correlation length of soil cohesion can have a large influence on footing bearing capacity, particularly for slopes with large height to footing width ratios. The paper demonstrates cases where a footing satisfies a deterministic design factor of safety of 3 but the probability of design failure is unacceptably high. Isotropic and anisotropic spatial variability of the soil strength was also considered. [ABSTRACT FROM AUTHOR]

This letter is concerned with the undrained bearing capacity of rectangular footings with various aspect ratios and embedment ratios in uniform clay. It covers thin plate foundations with low aspect ratios and high embedment depth with embedment ratio up to 150. The work is based on small strain finite element analysis (FEA). After verification of the FEA model against existing solutions of the bearing capacity factors of rectangular footings, a series of FEA results are obtained. Based on the FEA results, a simple formulation is proposed to calculate the bearing capacity factor for rectangle footing with different aspect ratio in any embedment depth, extending the existing solutions to cover a wider ranges of footing aspect ratios and embedment ratios. [ABSTRACT FROM AUTHOR]

The paper shows the increase in vertical and combined horizontal and moment bearing capacity of jack-up spudcan installed in silty clay, when a load-hold period is accounted for. The numerical implementation of a hypoplastic model for structured clays, combined with large deformation coupled analyses allowed the modelling of the spudcan installation process. Results were mapped into three-dimensional small strain analyses, conducted to investigate the combined loading capacity and describe the yield surface. The underlying failure mechanisms were investigated and increases in capacity due to consolidation determined. Experimental centrifuge data on carbonate silty clay validated the qualitative trend revealed numerically. [ABSTRACT FROM AUTHOR]

The tetrapod jacket foundations that are always used to support offshore wind turbines have been investigated primarily in laboratory experiments. In this study, the ultimate lateral soil resistance on this type of foundation was investigated using the finite element method and the analytical upper bound plasticity method. The numerical results show good agreement with the theoretical upper bound solutions under the same pile spacings ( S ) and soil-pile adhesion factors ( α ). Three distinct failure mechanisms (mechanisms A, B and C) were established in terms of different pile spacings. The ultimate lateral pressure was subsequently determined using numerical analyses with consideration of the loading direction. The most critical loading direction angles ( θ ) vary with the soil-pile adhesion factors, and are θ = 0 for α = 1 and θ = π/4 for α = 0. Selected empirical equations were proposed to predict the ultimate lateral bearing capacity for engineering practice, considering the pile spacing, soil-pile adhesion and loading direction. [ABSTRACT FROM AUTHOR]

Numerical limit analysis provides a powerful tool for assessing the bearing capacity of geo-structures. Recently, a quasi-kinematic procedure, that uses the cell-based smoothed finite elements and second order cone programming, has been developed for limit analysis of purely cohesive soil. In this paper a more generally applicable formulation associated with Morh-Coulomb failure criterion, capable of determining bearing capacity of cohesive-frictional soil, is presented. Computed bearing capacity factors of geo-technical engineering problems such as footings and slope stability are presented and compared with selected published results. It is shown that the current procedure can provide solutions of accuracy being at least as good as those obtained using existing finite element limit analysis, while less computational effort is used. [ABSTRACT FROM AUTHOR]

The coupled numerical manifold method (NMM) and discontinuous deformation analysis (DDA) are enhanced to simulate deformations of continuous soil and discontinuous masonry structures. An elasto-plastic NMM-DDA is formulated that incorporates elasto-plastic constitutive laws into incremental forms of the equation of motion. A node-based uniform strain element is applied to avoid volumetric locking, which often occurs in conventional NMM-DDA. The proposed method is applied to three fundamental boundary value problems: a beam bending problem, a bearing capacity problem of a footing, and a bearing capacity problem of a masonry structure. The method is verified through comparisons with conventional solutions. [ABSTRACT FROM AUTHOR]

A finite element method (FEM) model was developed to investigate the distribution and dissipation of the soil excess pore water pressure (EPWP) around large-diameter open-ended thin-wall steel pipe piles (LOTPs) driven by impact loads into saturated clay, in addition to the set-up effect of LOTPs. The initial pore water pressure (PWP) distribution and vertical bearing capacity of LOTPs after EPWP dissipation were analyzed through this numerical model. The EPWP mapped onto the FEM model was compared with previously reported distribution curves, revealing that the numerical results were generally similar to those of previous theoretical models. Following dissipation for 28 days, the load–settlement curves of LOTPs were compared with the results of several specifications; this indicated that the larger the LOTP diameter, the greater the similarity between axial bearing capacities calculated via the FEM model and the specifications. This FEM model could generally satisfy the requirements for analyzing the set-up effect of LOTPs. It was also found that the LOTP capacities were overestimated when the EPWP was neglected. Beyond 28 days, the pile bearing capacity did not increase because the dissipation of the EPWP was almost fully developed. An equation for predicting the set-up effect of LOTPs installed using impact hammers is also presented. [ABSTRACT FROM AUTHOR]

Bridge foundations located in a water flow environment commonly experience scour, which can lead to significant drops in the soil elevation immediately surrounding the foundation. This has significant ramifications for lateral bearing capacity as well as the integrity of the supported superstructure. While pile groups are one of the most foundation systems for bridges, current research on scouring effects has been largely limited to single piles. This paper fills this gap through the use of 3D finite element (FE) analysis, validated using centrifuge tests reported elsewhere in the literature. Results from a parametric analysis is described exploring the effects of the scour hole geometry, defined by the depth and slope angle, on the lateral behavior of pile groups. In particular, the influences on the load–displacement and bending moment and soil resistance distributions with depth for each pile within the group are considered. The results show that scour can have a significant detrimental influence on the lateral response of a pile group. An increase in the length of the pile group is also shown to significantly reduce the sensitivity of the lateral bearing capacity of the group to scour. [ABSTRACT FROM AUTHOR]

Excessive wave-induced pore pressure buildup around offshore foundations results in liquefaction, settlement and bearing capacity degradation, which may threaten the safety of Offshore Wind Turbines (OWTs). Despite the extensive research efforts on wave-induced seabed residual response in the recent years, there is still a lack of knowledge on mechanisms of wave-induced liquefaction and settlement around caisson foundations. Employing a code-based framework implemented in OpenSees, the cyclic response of wave-seabed-foundation (WSF) system is evaluated. Biot's consolidation theory, linear wave theory and CycLiqCPSP constitutive soil model are integrated to evaluate the response of soil-foundation system accounting for the hydrodynamic pressure of wave imposed on the seabed surface considering the fully-coupled wave-seabed-foundation interaction (WSFI). Soil model parameters are calibrated against cyclic simple shear (CSS) tests and the numerical model is validated by a well-documented centrifuge experimental model. Various seabed characteristics, and a range of the geometrical properties of foundation with different OWT weights are put into practice for evaluating the geotechnical aspects of wave-induced liquefaction. Stress paths are provided to demonstrate quite different level of reduction in effective stresses and likelihood of liquefaction occurrence upon cyclic shear stresses application for different locations in the vicinity of the foundation area. The present study will also improve understanding of the interplay among the state variables on the wave-induced foundation settlement and bearing capacity degradation allow to feed the output data into development of simplified procedure for assessing the bearing capacity. Finally, results from over 250 analyses with different model configurations are used to provide an estimate of wave-induced caisson settlement with reasonable accuracy on the basis of artificial intelligence (AI) method known as Group Method of Data Handling (GMDH). [ABSTRACT FROM AUTHOR]

A novel three-dimensional numerical model for the biaxial geogrid reinforcement is proposed in this paper that can incorporate the direction-dependent strength and stiffness properties and the actual grid-like structure of the geogrid reinforcement, which are crucial for soil-geogrid interactions. First, the numerical model consisting of cable structural elements is validated against wide width tensile test results reported in the literature. Next, the geogrid reinforcement model is validated with published experimental and numerical results on reinforced foundations. Two different cases, the bearing capacity of foundation in geogrid-reinforced soil and the uplift capacity of anchor plates in geogrid-reinforced sand, are selected from the literature for validation. The numerical results reasonably agree with the experimental results for both the bearing and uplift cases. The results indicate that the proposed approach can predict the behavior of geogrid reinforcement and can be used for modeling and analysis of other geogrid-reinforced structures. [ABSTRACT FROM AUTHOR]

The composite foundation reinforced by stone columns and vertical drains is widely used in various projects. However, available calculation methods for such consolidation are rarely reported in the literature. Firstly, a set of basic equations are proposed to describe the seepage relations among stone columns, vertical drains, and soft soils in this study. Then, the governing consolidation equation, in which the average total excess pore water pressure (EPWP) serves as a variable, is derived by considering the deformation of stone columns during consolidation under the assumption of equal strain conditions. Moreover, the analytical solution for the consolidation equation is obtained by the method of separation of variables, and its reliability is verified by degenerating into the solution for the consolidation of composite foundations reinforced by stone columns and comparing it with the field measurements. Finally, a parametric study is performed to investigate the consolidation behavior. The results show that the consolidation rate can be significantly increased by installing vertical drains between the stone columns compared to reducing the column spacing; for some composite foundations reinforced by stone columns with a high ratio of replacement, the deformation of columns during consolidation cannot be ignored; the smear effect caused by vertical drains can be ignored in such composite foundations. [ABSTRACT FROM AUTHOR]

In this paper, an analytical method and semi-empirical equations are presented for determining the bearing capacity failure envelopes for foundations subjected to inclined or eccentric loads in unsaturated soils considering the influence of steady and transient state flow conditions. Firstly, the analytical method is proposed extending the slip line theory coupled with analytical solutions for different matric suction profiles. The failure envelopes in the V - H (Vertical - Horizontal) and V - M (Vertical - Moment) loading spaces for two fine-grained soils were investigated by conducting parametric studies using the proposed method. The influence of the ground water table depth variation, internal friction angles, surface flux boundary conditions and different infiltration durations were considered. Based on the parametric studies results, semi-empirical equations were proposed for the failure envelopes in the two loading spaces. The validity of the proposed failure envelope equations is examined by providing comparisons with the proposed analytical method and published results from the literature. Good agreement is found between the fitted failure envelopes and that obtained from the analytical method and published studies. [ABSTRACT FROM AUTHOR]

The seismic bearing capacity of strip footings resting on unsaturated soils subjected to combined loading is investigated in this study using a combination of lower bound limit analysis and finite element discretization. Second-order cone programming (SOCP) is used in this instance to simulate the nonlinear form of the universal perfectly-plastic Mohr-Coulomb yield criterion during the stress field optimization process. Under no-flow and steady-state infiltration/evaporation flow conditions, the significant influence of matric suction induced below the surface footing is accounted for using the suction stress concept. The load eccentricity and inclination applied to the footing and pseudo-static forces exerted simultaneously to the footing (superstructure) and underlying soil are all incorporated into the equilibrium equations, resulting in combinations of limit moment (M), and vertical (V), and shear (H) forces, under the influence of seismic loading. The results demonstrate that the matric suction induced within the porous structure of the underlying soil stratum increases the capacity of the surface footing to withstand various combinations of eccentric and inclined loadings under seismic excitation. Moreover, at a given hydraulic condition, the failure envelopes of obliquely/eccentrically loaded shallow foundations shrink significantly with the increase in the seismic intensity; the process which is more highlighted in sand (no-suction and all flow conditions). As the flow state in the unsaturated clay changes from infiltration to evaporation, the failure envelopes are observed to enlarge. In addition, as the load inclination angle reaches the soil-footing interface friction angle, the ultimate horizontal bearing capacity of the foundation resting on sand (no-suction) drops to zero; however, there still exists a residual shear resistance in the underlying clay layer or unsaturated sand, posing non-zero horizontal bearing capacity even at extremely high angles of inclination. Last but not least, the influence of earthquake horizontal loading on the bearing capacity envelopes of a shallow footing resting on a sand deposit was corroborated to be more pronounced than on a cohesive soil deposit. Indeed, the intrinsic (residual) cohesion, normally found in cohesive soils, was realized to contribute significantly to suppress the detrimental effect of earthquake horizontal loading. [ABSTRACT FROM AUTHOR]

Soil-rock mixtures (S-RM) are pervasive in nature and are heterogeneous media with continuous and discrete properties. The S-RM slope has become one of the fundamental geological environments for engineering activities due to the constant growth of engineering construction. In this study, a slope system was constructed based on the discrete element method (DEM) to analyze the micro-scale phenomena of rock-wrapping in the slope shear band and the micro-scale mechanisms, including force chains and anisotropy, under the ultimate load-bearing state. The results indicate that the slope ultimate bearing capacity increased with rock content and angularity but decreased with aspect ratio and was also affected by the spatial distribution of rocks. During the slope destabilization process, there were at least four modes of rock-wrapping movement in the shear band, and the variability of soil and rock movement caused the irregularity of shear surface in the S-RM slope. The disturbance range of slope shear dilatation was heavily influenced by rock content and angularity, and the aspect ratio was an important factor in determining the morphological characteristics of shear dilatation. The content, distribution, and shape of rocks influenced the regularity of the distribution of force chains and the anisotropy of a slope. [ABSTRACT FROM AUTHOR]