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A large amount of excavation waste soil will be produced during highway construction, which will lead to environmental pollution and construction site occupation. To make full use of the excavation waste soil, hydraulic pile-forming equipment with a maximum pressure of 200 t is developed based on the principle of building clean transportation infrastructure. In addition, a precast pile with modified waste soil (PPMS) is proposed to achieve the large-scale consumption of the excavation waste soil. The PPMS has the advantages of regular shape, reliable quality, and stable bearing capacity. The relevant production standards and construction processes are proposed in this paper. The static pressure test analysis of the PPMS and lime–soil compaction pile was performed to verify the feasibility of the PPMS in reinforcing soft foundations. The test results show that the bearing capacity of a single PPMS could reach 600 kN. Under the upper load of 400 kPa, the settlement of the PPMS-reinforced soft foundation is 30% smaller than that of the lime–soil compaction pile. The PPMS has the advantages of high bearing capacity and economic and environmental protection, which is suitable for reinforcing soft foundations. [ABSTRACT FROM AUTHOR]

The ultimate bearing capacity of a strip footing placed horizontally over the edge of a sloping rock mass has been determined on the basis of the stress characteristics method (SCM) using the generalized Hoek–Brown yield criterion. The effect of footing–rock interface roughness on the results has also been analyzed. The problem has been solved, in addition, with the usage of the adaptive mesh–based finite-element limit analysis (FELA) method. The results are provided in the form of nondimensional bearing capacity factor (Nσ) as a function of different input material parameters for several slope inclinations. After analyzing all the results, an expression on the basis of the regression analysis has also been generated to compute the factor Nσ as a function of different input variables. The bearing capacity obtained from the SCM has been found to lie between the lower and upper bounds of the FELA, and the failure patterns from the two sets of analyses match quite closely with each other for both smooth and rough footings. The results are also found to be in good agreement with the existing solutions from the literature. [ABSTRACT FROM AUTHOR]

The bearing capacity of large rectangular foundations on soil subjected to combined loading [simultaneously subjected to vertical load (V), overturning moment (M), and horizontal or lateral load (H)] is one of the central topics of interest to geotechnical engineers as it relates to the design of foundations such as ground anchorages of bridges, offshore structures, and gravity dams. To solve this problem, a combination of numerical simulation and theoretical research was used, and a stability evaluation model of large rectangular foundations on soil subjected to combined loading was established. First, an empirical equation for the failure envelope in the V‒M‒H loading space of rectangular foundations was developed. Second, the safety factor for load-path dependency (LPD) was established by considering the combined effects of V, M, and H, the stability evaluation model for large rectangular foundations on soil subjected to combined loading was constructed by proposing a method for calculating the LPD safety factor based on the V‒M‒H failure envelope. Last, the accuracy and effectiveness of the stability evaluation model proposed was verified. The proposed model provides a convenient means of calculating the stability of large rectangular foundations on soil under combined loading. The model was applied to the optimal design of a gravity anchorage project of a suspension bridge, which proves that the proposed model is rational and efficient. [ABSTRACT FROM AUTHOR]

Cavities are common subsurface anomalies that have a significant impact on the bearing capacity of footings. While cavities behave three-dimensionally, in previous studies, the analysis of cavities has been limited to two-dimensional plane-strain analysis because of the time-consuming nature and complexity of three-dimensional modeling. However, this study demonstrates that the bearing capacity factor derived from three-dimensional modeling can be up to 10 times higher than that obtained from plane-strain analysis, highlighting the importance of considering three-dimensional effects. The present paper conducted three-dimensional simulations to investigate the impact of spherical cavity on the failure mechanisms and bearing capacity of footings under undrained conditions. An extensive parametric study was performed to investigate the influential parameters, including footing width to cavity dimension ratio (B/D), cover depth ratio (C/D), overburden factor (γD/Su), and void eccentricity ratio (S/D) for both circular or square footings. The results indicate that increasing the overburden factor and void eccentricity ratio leads to a decrease and increase in the bearing capacity of the footing, respectively. Furthermore, changes in other parameters can either increase or decrease the bearing capacity depending on the characteristics of the cavity (size and location) and footing (size and shape). General solutions for the bearing capacity factor are provided for different variations of the dimensionless parameters. This study also examined various failure mechanisms, including both cavity-independent and cavity-dependent failure mechanisms, associated with circular and square footings and influential parameters. These mechanisms are categorized into three zones for cavity-independent failures and four zones for cavity-dependent failures. The changes in the influential parameters including B/D, S/D, γD/Su, and C/D lead to changes in the type of failure mechanism and the size of the failure zones, while the foundation shape does not have a significant effect on the failure mechanism. Sinkholes and underground cavities annually contribute to infrastructure damage and financial losses. The 1981 incident in Winter Park, Florida, exemplifies the real-world consequences. Previous investigations have been limited to two-dimensional models due to the time-consuming nature and complexity of three-dimensional modeling, but the real-world nature of cavities in three dimensions requires a more comprehensive understanding. This study directly addresses this need by investigating the impact of three-dimensional cavities on the bearing capacity of circular and square building foundations, also known as footings. This study thoroughly investigated the factors influencing the results, encompassing cavity size, depth, soil weight, and off-center position. It extensively explored potential footing failures, providing detailed discussions. Our findings are presented as easy-to-understand maps and charts covering a broad range of potential scenarios. These visual tools can help engineers and researchers accurately estimate the stability of a building's foundation when a cavity is present underneath. In simpler terms, this research has created a handy tool for professionals to predict the potential danger posed by hidden cavities to buildings and infrastructure. This knowledge can then be applied to ensure safer building practices, potentially saving a significant amount of money and preventing accidents in the future. [ABSTRACT FROM AUTHOR]

This study presents a new solution algorithm to calculate the bearing capacity coefficient Nγ for a fully rough strip footing located on an infinite slope considering different soil friction angles φ and ground slopes β° using the stress characteristics method. The results showed that Nγ coefficients decreased with an increase in slope inclination, and roughness contribution prevented further reduction, particularly for higher φ values. The higher contribution of the upside-sloping ground for footing laid on the infinite slope led to a lower reduction of the Nγ coefficients compared with the footing placed at the slope vicinity in terms of a larger area affected by the stress field, and a larger plastic region of the downface slope. The reduction value was more eminent for steeper slopes β ≥ 20° due to the tendency for nonsymmetrical failure pattern, especially for higher φ values. The findings of the current research and those described in the literature were in good agreement, so much so that the lower-bound limit analysis and the current solution technique virtually reflect the same trend. The load inclination values for footings located adjacent to the slope with β ≤ 30° were not meaningful, whereas for footing resting on an infinite slope with β ≥ 25° it exceeds 15°, which reflects the fact that its effect should not be neglected, especially for ground slopes greater than 20°. By increasing β°, the maximum values of plastic length and plastic depth on the left and right sides of the footing decrease and increase, respectively. The maximum depth of the plastic region for β ≥ 20° from around the right side of the footing shifts toward the downward-sloping face. The maximum width of the elastic wedge gradually reduces, and the intersection point of the left and right plastic regions slowly shifts to the left and upside of the footing. [ABSTRACT FROM AUTHOR]

The strength anisotropy and strain softening of natural soil can significantly impact the bearing capacity of shallow foundations on clay. In this article, we present a nonlocal numerical method to study the coupled rotation of the maximum normal stress axis and strain softening on the bearing capacity of shallow foundations on clay through a Cosserat strain softening constitutive model. The strength anisotropy and strain softening characteristics were numerically implemented into a finite-element (FE) program by dynamically updating the anisotropic cohesion in global Newton–Raphson iterations. Due to its nonlocal feature, the proposed nonlocal numerical method can overcome the mesh dependence in simulating the progressive failure of clay through the classical FE method. We first validated the efficacy of this method against the results of the plane strain test and numerical results in the literature. We then study the bearing capacity of a strip footing over anisotropic and strain-softening clay through the implemented numerical method. The results indicated that the deposition angle has an important effect on the bearing capacity and failure mode. The effects of the degree of anisotropy and strain softening on the ultimate bearing capacity are quantified through the numerical method. It is found that (1) the proposed method can effectively reflect the characteristics of the maximum normal stress axis rotation on the failure surface of the footing; (2) the ultimate bearing capacity of a footing (Pu) on anisotropic clay could increase linearly with an increase in the anisotropy ratio k (i.e., k is the ratio between C1 and C2) and decreases with an increase in the softening modulus; and (3) the strength anisotropy and strain softening are strongly coupling factors impacting the bearing capacity of anisotropic clay. [ABSTRACT FROM AUTHOR]

The aim of this study is to investigate the influence of the anisotropic variability in soil on the failure mechanism and the ultimate bearing capacity of foundations that are placed near slopes. A random adaptive finite-element limit analysis (RAFELA) with anisotropic random field modeling and the Monte Carlo simulation technique are combined. The stochastic ultimate bearing capacity for various undrained shear strengths, slope angles, normalized slope heights, distances from the slope crest, and horizontal and vertical correlation distances are analyzed. The quantitative identification and characterization of failure mechanisms, which are determined by the failure slip and passive wedge contribution, are achieved through the digital image processing of realizations from anisotropic random soil. This study showcases the diverse failure mechanisms and sliding surface sizes that arise from distinct soil patterns, which are influenced by alterations in slope geometry and soil anisotropic spatial variability. The quantitative findings highlight that alterations in failure mechanisms and slip surface sizes lead to heightened failure probabilities and significant variations in bearing capacity. [ABSTRACT FROM AUTHOR]

Geocells have recently been widely used to reinforce subgrade/foundation soil beds. The honeycomb-shaped cells can significantly improve the apparent cohesion and stiffness of soil due to the lateral limitation. This paper aims to predict the subgrade modulus of geocell-reinforced sand beds according to the unreinforced soil and the properties of geocells. Numerical technology was adopted to obtain the original data used for building the predicted model. A laboratory plate load test was initially cited to validate the calculated results obtained using FLAC3D. The validated model was subsequently extended to the baseline model of geocell-reinforced sand beds. The influence of reinforced parameters on bearing capacity and subgrade modulus was discussed deeply. The results revealed that only sufficient lateral deformation could increase the passive resistance of geocells. Based on this, the predicted model was proposed by considering the applied load, unreinforced soil, and geocell parameters. Furthermore, a modified equation was also built to suit all sand with different relative densities. The comparison results showed the suitability and accuracy of this model. [ABSTRACT FROM AUTHOR]

A sand compaction pile (SCP) with a high area replacement ratio (>50%) has been recently employed to improve the soft clay ground in offshore projects, but its performance is still not completely known. Therefore, to provide a comprehensive understanding of the SCP method, a series of laboratory model tests were performed on the SCP-improved clay ground using high (70% and 100%) and the low-to-medium (0%, 14%, and 38%) area replacement ratios. The internal stress and strain responses of SCP-improved ground with a high area replacement ratio were different from those with a low-to-medium ratio. Typically, under high ratios, the loaded SCPs bulged, resulting in the bending of the adjacent SCPs, while under low-to-medium ratios, the SCPs deformed individually. Essentially, the additional lateral confinement is provided by the adjacent SCPs under the high replacement ratio. An improved model to predict the bearing capacity of the SCP-improved ground was proposed by incorporating a coefficient of lateral pile interaction that reflects the failure mechanism. The prediction using the proposed model showed good agreement with the observations in the west artificial island of the Hong Kong–Zhuhai–Macao Bridge project. This study provides a universal mathematical model to predict the bearing capacity of the clay ground improved by SCP varying from low to high area replacement ratios, leading to a comprehensive understanding of the performance of this modern technique. [ABSTRACT FROM AUTHOR]

This paper focuses on the bearing capacity of vertically loaded rigid footings adjacent to slopes with spatially random soil by performing random adaptive finite-element limit analysis. The solution is illustrated by quantitatively assessing the effect of influential factors, taking into account the spatial variability, soil properties, and geometric parameters on the ultimate bearing capacity and failure mechanism. The variability of the slip surface, which has several failure mechanisms, is investigated for various normalized slope heights, footing distances, slope angles, and spatially variable soil cohesions. Different possibilities of failure mechanisms and sliding surface size resulting from these soil patterns are demonstrated with changes in slope geometry and soil spatial variability. The results quantitatively reveal that a high failure probability with a large variation in bearing capacity is induced by the changes in the failure mechanism and slip surface size. [ABSTRACT FROM AUTHOR]

Square foundations often penetrate deeply into seabed sediments so that sufficient bearing capacity is obtained, which inevitably induces large-scale deformation in the surrounding sediments. Most of the previous research on square foundations has assumed the sediment had a uniform or linearly increasing strength profile with depth and has ignored the spatial variability of sediments. This work therefore focused on the influence of sediment spatial variability on the behavior of square foundations by applying a random large-deformation finite-element (LDFE) approach. The LDFE results indicated that the sediment heave effect could increase the bearing capacity by up to 15%. This underscores the advantages of LDFE analysis for bearing capacity predictions. More importantly, the mean bearing capacity from random analyses is smaller than the deterministic solution in uniform sediments. Consequently, deterministic analysis yields an overestimated bearing capacity. Finally, a framework was established for estimating the probability of failure at various depths considering a random sediment strength based on a factor of safety (FOS). This indicated that the partial FOS recommended by the Det Norske Veritas code is equivalent to a probability of failure of 0.1%. Our findings may facilitate the evaluation of the probability of failure for deterministic foundation design based on the FOS. [ABSTRACT FROM AUTHOR]

This study evaluated the strip foundation bearing capacity and settlement on sandy soil reinforced with scaled geocomposite and geotextile by laboratory model testing. Therefore, several reinforcement compounds were used in different layers (one to four), including identical and various vertical distances from each other and the footing base. The geocomposite used in this study consisted of geogrid and geotextile layers. The most crucial consideration in this research was the application of scaled reinforcement with a factor of 7.5 to create more precise laboratory models. Based on the results, all models failed in the lower settlement, which in most cases was 7% of the width of the footing. Test results indicated that the maximum increasing factor in bearing pressure of foundation in the case of ultimate bearing was 3.4, which could be related to using four layers of geocomposite at optimal distances. The percentage of decreasing footing settlement at the maximum value was about 86% in the two-layer geocomposite state. Its value remained constant with increasing number of layers. Percentage variation in bearing capacity value indicated that geotextile had a better performance in increasing the bearing capacity at the high settlement level. It was close to the values of the geocomposite. [ABSTRACT FROM AUTHOR]

The undrained bearing capacity of ring foundations has received significant attention from researchers, but most of the reported studies do not reflect the effect of consolidation due to preloading. In this work, we investigated the postconsolidation undrained vertical capacity of ring foundations resting on nonhomogeneous clays using finite differential analyses and the modified Cam-clay constitutive model. The results are presented in nondimensional form and were compared with data available in the literature. The coupling influences of the internal opening of the foundation, the magnitude of the preloading, the duration of the consolidation, and the initial overconsolidation ratio of the clay were all considered. A methodology based on approximating expressions that captured the numerical results well is proposed as a way of predicting the undrained capacity gain of ring foundations for any degree of preloading and consolidation. [ABSTRACT FROM AUTHOR]

Torsional load arising from horizontal load eccentricity has a significant effect on the ultimate horizontal load carrying capacity of tripod bucket foundations in clay. In this paper, the effect of torsional load on the failure mechanism and ultimate horizontal capacity of tripod bucket foundations in undrained clay was studied using 3D finite-element analyses. Three single buckets were connected to form a rigid tripod bucket foundation system. Two different shear strength profiles, that is, uniform and linearly increasing with depth were considered. A detailed parametric study was conducted by varying the bucket spacing and embedment depth to explore the effects of different governing parameters. All the analyses were carried out for smooth and rough interface conditions. The influence of torsion on horizontal capacity is presented in the form of combined horizontal-torsional (H-T) failure envelopes. Reductions in ultimate horizontal capacity with increasing load eccentricity were quantified for the ease of practice. Finally, an expression for estimating combined H-T capacity is provided as a function of normalized spacing and embedment. Additional analyses were also performed to evaluate the effect of moment arising from vertical eccentricity on the combined H-T capacity. [ABSTRACT FROM AUTHOR]

The paper aims to evaluate the pseudostatic seismic bearing capacity of shallow foundations on geosynthetic-reinforced granular soil subjected to inclined/eccentric combined loading. This is achieved through a comprehensive set of lower-bound finite-element limit analysis (LB FELA) simulations adopting the second-order cone programming. The pseudostatic seismic loading is incorporated into the element equilibrium equations as body forces. Both sliding and structural modes of geosynthetic failure are simulated within the FELA framework. The influences of pseudostatic acceleration, embedment depth (u), and the ultimate tensile strength (Tu) of the reinforcement layer on the failure mechanism, bearing capacity ratio, and failure envelope of the overlying obliquely/eccentrically loaded shallow foundation are thoroughly investigated and discussed. It is generally concluded that at a given reinforcement embedment depth, failure envelopes shrink substantially with the increase of the seismic horizontal acceleration and the reduction of the geosynthetic ultimate tensile strength. [ABSTRACT FROM AUTHOR]

Reasonable estimation of the bearing capacity of bulbs is essential for the design of squeezed branch pile (SBP) foundations, and existing analytical methods cannot be applied to SBPs. This study investigated the bearing capacity of bulbs by model tests, field tests, and theoretical and numerical analysis. From the laboratory model loading test and transparent soil model test assisted by particle image velocimetry technology, the bearing features of SBPs and the displacement field around a bulb under failure state were investigated, respectively. It was found from the tests that the bulb's bearing ratio is up to approximately 50% out of the total applied load to the pile at failure. Furthermore, by referring to Meyerhof's theory of bearing capacity for deep foundations, an analytical method was proposed to calculate the bearing capacity of a bulb for an SBP considering its unique geometry. Finally, field tests with a real-size SBP and numerical study were conducted to verify the proposed method. The ultimate bearing capacity (UBC) of the bulb estimated by the proposed method has an acceptable difference of 4.21% from the model test and 17.6% from the numerical field cases. The proposed solution can be used as an effective explicit solution to evaluate the UBC of the single bulb of SBPs considering the pile's dimensions and soil parameters. [ABSTRACT FROM AUTHOR]

This paper attempts to investigate the bearing capacity of a strip footing that rested on unsaturated homogenous sands and used upper bound finite-element limit analysis in association with linear optimization. The analysis is based on suction stress-based (σs) effective stress (σ′) analysis. Unlike the saturated soil, the size of the yield surface varies with the vertical position, and therefore, proper modifications are carried out in the upper bound formulations to incorporate the unsaturated soil property functions. A detailed investigation is carried out to estimate the load-carrying capacity of a strip footing that vary the mechanical strength, unsaturated soil properties, water table depth (hw), and climatic conditions. The numerical solutions are presented in terms of bearing capacity factors [BCF (Nγs, Nqs)] for the unit weight (γw) and surcharge pressure (qs). The nodal velocity patterns are drawn for several cases, and the presented solutions are compared with the available results. The design charts provided in this paper might be useful to design engineers. [ABSTRACT FROM AUTHOR]

This paper presents the results of finite-element analyses of rigid-surface strip foundations on dry cohesionless soil subjected to displacement-controlled vertical loading. A two-surface constitutive model with a non-associated flow rule, representing the full range of pressure-dependent drained shear strength and volume change behavior of dry sand, is employed to model the soil. A range of foundation widths and sand initial relative densities is covered. The results show that, for narrow, rigid-strip foundations, the conventional bearing-capacity calculation provides a reasonable indication of the load-carrying capacity of the foundation. However, there is no peak in the load-carrying capacity for wide foundations, and the load–deformation curve exhibits stiffening behavior, even at large settlements; this is particularly apparent at larger values of the initial relative density. Based on the results, it is observed that with the increase in vertical foundation loading, the vertical stiffness of the foundation increases with each loading increment, due to the tendency of the dense sand to become more dilatant with the increase in confining pressure. At large settlements, the state of the sand beneath the foundation approaches the critical state. Settlement vectors beneath the foundations on dense sand reveal that the displacements approximate one-dimensional compression. [ABSTRACT FROM AUTHOR]

Soils above the groundwater table and near the ground surface are often partially saturated, and the changes in the degree of saturation and matric suction caused by infiltration may have substantial effects on the stability of geotechnical systems. This work evaluates the significant effect of transient flow on the ultimate bearing capacity of strip footings founded on unsaturated soils under the simultaneous actions of vertical and horizontal loads and moment using the lower-bound theorems of the finite-element limit analysis and the incorporation of second-order cone programming. The unified effective stress theory is incorporated into the soil yield function to model the partially saturated state, and the closed-form solution for one-dimensional transient flow is adopted so as to evaluate the tempo-spatial variations of suction stress. For both sand and clay underlying soils, it is found that the increase of infiltration time leads to a notable decrease of the size of the normalized failure envelopes for either obliquely or eccentrically loaded shallow foundations. The impact of transient flow on the ultimate bearing capacity of surface footings is also observed to be greater for clay soils as compared with sand deposits due to the significant contribution of higher induced suction stress. [ABSTRACT FROM AUTHOR]

Finite-element limit analysis (FELA) is an effective numerical method to evaluate the stability of reinforced geostructures. Such an analysis has been commonly performed in the literature by assuming the earthen material to follow the well-defined associated plastic flow rule. In this study, the effect of adopting the nonassociated plastic flow rule on the ultimate bearing capacity of eccentrically-obliquely loaded shallow footings placed over geosynthetic-reinforced granular soil is rigorously examined through a comprehensive set of lower-bound FELA simulations along with second-order cone programming. The nonassociativity of the plastic flow rule is incorporated into the formulation of the Mohr–Coulomb yield criterion by considering a wide range of dilation angles (ψ) varying between 0 and the soil internal friction angle (φ). Unlike the previous FELA studies, both pull-out (sliding) and tensile (structural) modes of geosynthetic failure are taken into account. Accordingly, the impact of considering the nonassociated flow rule for the sand deposit on the bearing capacity ratio, failure envelopes, and the failure mechanism of overlying shallow foundation is investigated and discussed. The results show that failing to consider the significant influence of nonassociativity in the FELA simulations leads to overestimations of the tensile forces mobilized in the reinforcement layer as well as the ultimate bearing capacity of the overlying shallow foundation, thus yielding nonconservative and insecure designs. [ABSTRACT FROM AUTHOR]

Vertical stone columns have been employed to improve the bearing capacity of the foundations for circular oil storage tanks placed on weak clayey strata. A solid stone column was placed along the axis of the foundation along with (1) two annular rings of stone columns for a 10-m-diameter tank, and (2) four annular rings of stone columns for a 20-m-diameter tank. The tank was first placed on a thin granular pad before transferring the load to the underlying weak clayey stratum reinforced with stone columns. The bearing capacity, with and without vertical stone columns, has been determined by employing an axisymmetric finite-element limit analysis. The Mohr–Coulomb yield criterion was used for the granular pad as well as stone column materials, and the Tresca yield criterion was employed for the purely cohesive clayey stratum. The results from the analysis were compared with that reported in the literature. The employment of stone columns leads to a significant increase in the bearing capacity of the foundations on soft clay. [ABSTRACT FROM AUTHOR]

The bearing capacity of foundations constructed on unsaturated soils depends on the soil saturation degree and thus the soil suction. This paper presents a simple limit equilibrium approach to compute the foundation bearing capacity on unsaturated soil using lateral earth pressure theory. An imaginary retaining wall is assumed to pass the edge of the foundation and active and passive lateral pressures on both sides of the wall are computed using the distribution introduced in an earlier study. Equating total active and passive thrusts on two sides of the wall gives the footing bearing capacity. The soil–water characteristic curve is used to obtain soil suction corresponding to different moisture contents and drained shear–strength parameters are used to determine the foundation bearing capacity. The developed method is applicable to sands and c-φ unsaturated soils with varying saturation degrees. The predicted results have been compared with data from seven case studies reported in the literature and found a satisfactory agreement. Parametric studies have been conducted to investigate effects of foundation embedded depths, two-layer soils, various suction stresses, and ground slope changes on the footing ultimate bearing capacity. The results show that with increasing the soil suction, the footing bearing capacity increases significantly. [ABSTRACT FROM AUTHOR]

This paper pertains to the finite-element lower-bound bearing capacity analysis of inverted triangular-based strip footings (ITBFs). The solutions are obtained by the construction of a linear stress field that satisfies all the equations of equilibrium, which is the same as that developed by Lysmer in 1970; however, they were modified in conjunction with a nonlinear programming technique (active set algorithm) to isolate the optimal solution. Studies have been conducted on the convergence of the solutions (by varying the number of triangular elements), and the extensibility of the chosen stress field was confirmed by extending the mesh and comparing the solutions that were obtained. Parametric studies were carried out by varying the cone apex angle (β), for relevant soil properties and different values of the coefficients of earthquake acceleration [horizontal (αh) and vertical (αv)]. A close examination of the obtained results shows that they were as expected and were similar to those of conical footings. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate the behavior of strip shell footings subjected to axial and eccentric loads resting on a cylindrical steel rods assembly that simulates granular soil. An image processing analysis called particle image velocimetry (PIV) is used to obtain the displacement field around the footings. The bearing capacity and ultimate settlements of the footings are presented that show a linear variation with respect to the footing peak angle. The efficiency of eccentrically loaded shell footings is also discussed using settlement and rotation factors. Shell footings are proven to demonstrate better performance under eccentric loading in terms of settlement compared with axial loading cases, while a better performance is found at low eccentricities in terms of rotation. The PIV analysis provided the opportunity for a deeper comprehension of ground wedges beneath the footing and a comparison of results with analytical methods that validated the experimental results. Eventually, an eccentricity factor is proposed for the upper-bound solution to make it applicable for nonaxial loading cases. [ABSTRACT FROM AUTHOR]

A buried bucket foundation combined with a vertical truss is a new foundation system for photovoltaic farms in marine tidal flat (MTF) areas with deep soft soil. This paper employs numerical methods to study the response of the new buried bucket foundations in MTF clay under combined loading conditions. The ultimate limit states under combined static loads in the operation phase are presented as failure envelopes expressed in terms of geometric variations of foundation length and overburden soil depth, soil properties of MTF clay, and applied loads. A parametric study was carried out, and a soil failure mechanism was found from numerical studies for the newly proposed bucket foundations in MTF clay under general loading. A design method was established, which can be used for preliminary assessment of the bearing capacities of buried bucket foundations under combined loading conditions. [ABSTRACT FROM AUTHOR]

This study presents the numerical solution for the seismic bearing capacity of embedded strip footing in Hoek–Brown rock mass. The upper-bound solutions are presented by employing the finite-element limit analysis. The influence of various parameters namely, geological strength index (GSI), yield parameter of the rock (mi), rock strength ratio (σci/γB), embedment depth ratio (d/B), and the horizontal seismic coefficient (kh) on the seismic bearing capacity factor (N) of strip footing is assessed. The results are presented as design tables and charts for a wide range of parameters. A parametric study is performed and a discussion on the influence of each parameter on the seismic bearing capacity factor is made. The influence of the considered parameters on the failure pattern is highlighted. It is noted that the lateral extent of the failure surface increases with an increase in the depth of embedment which has a positive influence on the seismic bearing capacity of strip footing. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Finite element analyses are performed to investigate the influence of layered clays on the undrained response of embedded strip footings under uniaxial and combined loading. A fully bonded footing–soil interface was considered to comply with the undrained condition. Transformation in failure mechanism under uniaxial (vertical, horizontal, and moment) loading due to the involvement of the soft/strong underlying clay is extensively studied. Analysis-based bearing capacity values of strip footing for different combinations of embedment, top layer depth, and shear strength ratio are provided. The present study accounts for the interaction between coupling of horizontal and rotational displacements and underlying clay layer properties while investigating the combined load response. Subsequent effect of this interaction on the maximum and ultimate horizontal and moment capacities are quantified. In addition, the contribution of different footing and soil properties in altering size and obliquity of the failure envelope is categorically studied. [ABSTRACT FROM AUTHOR]

The bearing capacity of large strip foundations under combined loading is an important issue in geotechnical engineering, which is related to the design and stability analysis of foundations such as gravity dams, retaining walls, and ground anchorages of bridges. Herein, a new model for predicting the bearing capacity of large strip foundations under combined loading was proposed. First, a series of numerical simulation analyses of a large strip foundation resting on the surface of the soil were conducted to investigate the shape of the failure envelope in the V–M–H (vertical load, overturning moment, and horizontal load) loading space, and an improved form of failure equation was proposed. Second, the main factors influencing Vmax (the vertical ultimate bearing capacity) and the shape of the failure envelope were determined. Last, an applicable empirical equation of the failure envelope in the V–M–H loading space was presented. The results show that the deflection angle of the ellipse (θ), which is considered as a certain constant by previous studies, varies with the vertical load (V); the width of the foundation (B), the depth of the foundation (D), the cohesion of the soil (c), and the internal friction angle of the soil (φ) are the main factors influencing Vmax and the shape of the failure envelope; only parameters B, D, c, φ, and γ are needed to determine, in a unique way, the empirical equation of the failure envelope in the V–M–H loading space. The proposed model provides a convenient means of calculating the bearing capacity of large strip foundations on soil under combined loading. [ABSTRACT FROM AUTHOR]

The primary focus of the present article is to evaluate the bearing capacity of ring footing placed over two-layered soils and subjected to vertical loadings applied over certain portions of the footing, namely, inner half, middle half, and outer half. The layered soils are chosen as (i) sand over sand and (ii) undrained clays overlying on another layer of undrained clays. The combined effect of layer strength, ring geometry, top layer thickness, soil–footing roughness, surcharge loading, and loading positions are extensively verified by using axisymmetric lower-bound theorem of limit analysis in conjunction with finite elements and nonlinear optimization. An interior-point method based on logarithmic barrier function is employed to carry out the nonlinear optimization. The sand and the clay layers are modeled with the smoothened Mohr–Coulomb and Tresca yield surfaces, respectively. The results are reported in terms of normalized bearing capacity and efficiency factor. The magnitude of normalized bearing capacity appears to be highly influenced by the position of applied loading, whereas the efficiency factor and the optimum upper layer thickness are found to be unaffected by the zone of loading positions. Failure patterns are drawn for several cases. [ABSTRACT FROM AUTHOR]

In this paper, upper bound limit analysis that includes a horizontal pseudostatic seismic force is used for the first time to obtain the limit load on strip footings seated on cohesive-frictional soils reinforced with a single geosynthetic layer. Reinforcement tensile rupture and sliding failure modes for the geosynthetic layer are included in the analyses. Results of analyses are presented as optimum reinforcement depths and a bearing capacity equation with a single term and different bearing capacity factors for tensile rupture and sliding failure modes. The bearing capacity factors are presented in tables and capture the combined influence of the reinforcement strength, soil frictional strength and cohesion, soil unit weight, footing geometry, uniform surcharge, and magnitude of horizontal ground acceleration. [ABSTRACT FROM AUTHOR]

In this study, the bearing capacity coefficients Nγ were calculated for strip footings by considering different friction angles along the soil–footing interface (δ) using the numerical algorithm based on the method of stress characteristic lines. Changes in the geometric properties of plastic and nonplastic regions were also evaluated under the influence of footing roughness for different internal friction angles. The results revealed that the Nγ coefficient gradually increases with increasing roughness. At least 85% of the Nγ coefficient was achieved by mobilizing only 50% of the footing roughness. In addition, the magnitudes of Nγ under a full roughness state for φ > 25° were obtained, which were almost twice that of the smooth footing case. It was found that increasing the values of φ and δ/φ resulted in the expansion of the width and depth of plastic and nonplastic domains. Similar to the observed trend for the Nγ coefficient, the major part of the maximum width and depth values of plastic and nonplastic regions obtained under complete roughness state were provided for φ ≥ 0.5. By increasing both φ and δ/φ, the curvature of the outer boundary of the nonplastic curved wedge increases and affects a deeper layer of the soil. Further, the emergence point of the curve tends toward the footing edge, therefore the wedge covering a wider part of the footing base. [ABSTRACT FROM AUTHOR]

Ring foundations are widely used to support various types of offshore structures because of the cost-effective reason. Unlike the traditional circular foundations, very few studies were reported with regard to the bearing capacity of ring foundations. In addition, the study on the stability effects of anisotropic and nonhomogeneous clays is yet to be found in the current literature. The purpose of the technical note is therefore to bridge the current research gap. By using the robust lower and upper bound finite-element limit analysis in axisymmetric conditions, new stability solutions of ring footings on anisotropic and nonhomogeneous clays are obtained using dimensionless parameters. The associated failure mechanisms are also examined and discussed, while the design equations are proposed for predicting the bearing capacity of ring foundations. The findings in this study provide a reliable solution to improve the current design standard for ring footings in anisotropic and nonhomogeneous clays. [ABSTRACT FROM AUTHOR]

This paper deals with the behavior of piles subjected to inclined compressive loads. Some numerical results are first presented to document the influence of the load inclination on the pile response to high loads capable of determining an ultimate condition of the soil–pile system. On the basis of these results, a simple-to-use approach is proposed for a preliminary evaluation of the bearing capacity of piles embedded in cohesionless soils as well as in cohesive soils. Comparisons with numerical results and experimental data from model pile load tests are presented to assess the reliability of the proposed approach. A fairly good agreement is found in all considered case studies. In addition, it is shown that the predictive capability of the present approach is better than that of other simplified methods published in the literature. [ABSTRACT FROM AUTHOR]

In this study, the Taguchi design of experiments (TDOE) is employed to enhance the bearing capacity of geotechnical structures. To this end, two different case studies, including tapered helical piles as a novel kind of deep foundation (Case 1) and a shallow foundation resting on braid-reinforced soil as a new type of soil reinforcing technique for shallow foundation beds (Case 2), are studied. A series of large-scale tests, including pile loading tests in frustum confining vessel (Case 1) and standard plate load tests in test pit (Case 2), have been conducted in conjunction with numerical analyses. To the best of the authors' knowledge, this study is the first of this kind that uses the capability of the TDOE method to evaluate and improve the bearing capacity using large-scale tests. After conducting the tests, analysis of signal-to-noise, analysis of means, and analysis of variance were used to interpret the experimental results, to obtain the optimum condition, and to determine the percentage of each factor's participation in bearing capacity. Moreover, the Taguchi method output predictions are compared with the test observations and numerical modeling results. The comparison between test results and TDOE method predictions confirms that the Taguchi method can predict the bearing capacity well (R2 > 0.95). Additionally, verification tests on optimum models show a low level of relative error (RE < 5%) between the TDOE predictions and test results for both the case studies. Therefore, the results prove the ability of the TDOE method to predict and determine the optimum condition in geotechnical bearing capacity problems. [ABSTRACT FROM AUTHOR]

The foundation bearing-capacity characteristics and differential settlement have become the vital issues of high-speed rail study. Because of the collapsibility around loess foundations, the bearing characteristics as well as differential settlement are significantly different from other soil foundations. At present, there are many studies on other types of soil foundations, while the bearing capacity characteristics and differential settlements of the column-hammered and thrusted-expanded pile (CHTEP) composite foundation in the collapsible loess area are rarely involved. Therefore, based on the current codes, field tests and finite-element method (FEM), the variation in the differential settlement and bearing capacity characteristics of composite foundations with CHTEP is studied in collapsible loess areas. This paper mainly obtains the changing law of pile body stress, pile–soil stress ratio, pile side-friction resistance, differential settlement about the pile, and the soil between the piles of the composite foundation with CHTEP during different construction conditions. The result also shows the bearing capacity and settlement about composite foundation with CHTEP is up to code. This paper can provide some important rule to the design or construction about composite foundations with CHTEP at collapsible loess areas or other similar cases. [ABSTRACT FROM AUTHOR]

The ideal notion of footings placed in isolation is rarely implemented in practice and footings are often placed adjacent to each other, interfering with one another's performance. In this paper, the lower-bound finite-element limit analysis method is used to investigate the pseudostatic bearing capacity of a strip footing placed in close proximity to an already-existing strip footing, over cohesionless soil. The pseudostatic approach is used to model the seismic loading. Analyses conducted for different accelerations, soil friction angles, and service load magnitudes on the existing footing and spacings showed that while the presence of the existing footing can improve the pseudostatic bearing capacity of the new footing, an amplified rate of reduction with seismicity ultimately causes the new footing to withstand smaller accelerations compared with its isolated case. The increase in spacing generally reduced bearing capacity. An exception was observed for a friction angle of 40° for all service loads and pseudostatic accelerations, where a maximum in both bearing capacity and fluidization acceleration was observed around 0.1 of the footing widths. [ABSTRACT FROM AUTHOR]

This study aims to establish an equation to obtain the optimum tapering angle (αopt) for bored tapered piles that is correlated with pile geometry and sand properties that vary with the relative density. This αopt corresponds with the maximum axial bearing capacity when the volume of material in the tapered pile is maintained identical to the counterpart straight cylindrical pile. First, analytical formulations will be developed to estimate the axial bearing capacity of bored tapered piles that are embedded in sand. The proposed governing equations capture the shaft vertical bearing component of the tapered pile, which is unique to tapered piles and varies nonlinearly with the tapering angle (α). By differentiating the obtained bearing capacity equation for α, an αopt is achieved. The finite element method (FEM) will be adopted to conduct the numerical modeling and to calibrate the model parameters of the proposed analytical equation, which considers soil nonlinearities and interactions between the tapered pile and the surrounding soil that is subjected to axial loading. The UBCSAND constitutive model will be used to simulate the soil response near the tapered pile and the model parameters will be calibrated against laboratory test results for sandy soils with different relative densities. However, due to the complexity of the proposed differentiation and inverse calculation, a numerical solution will be used to obtain the results. Then, the load–displacement curves of the tapered piles will be attained numerically and αopt, which results in the maximum axial capacity of the pile, will be determined. The results exhibit good agreement between the analytically determined axial bearing capacity for the tapered pile and the corresponding numerical modeling predictions. Furthermore, a simplified empirical equation will be established to select αopt, which could be used by practicing engineers. [ABSTRACT FROM AUTHOR]

With wind farm development, a new type of foundation, the piled beam–slab foundation, was invented to support wind turbines on land. Although this foundation enables a lower-cost investment, its structure is complex. Wind turbine foundations are usually subject to combined vertical, horizontal, and moment loads. To investigate the coupled effects on the piled beam–slab foundation, scaled model tests were conducted. The results show that the presence of a vertical load increases the horizontal bearing capacity of the piled beam–slab foundation. The axial forces of the piles are mostly caused by the vertical load and moment acting on the foundation. The vertical load carried by the piles increases when the horizontal load acting on the foundation increases or the moment acting on the foundation decreases. Several equations are proposed to calculate the responses of the foundation under a combined load based on the responses of the foundation under a pure horizontal or moment load, which can be calculated by the traditional design method. Finite-element analysis on a prototype piled beam–slab foundation is performed to prove that the proposed equations are reasonable for actual foundations. [ABSTRACT FROM AUTHOR]

A probabilistic study on the bearing capacity of two parallel strip footings on a spatially variable soil where the mean of undrained shear strength increased linearly with depth was performed. For the comparative purpose, the single footing case was also investigated. Stationary and nonstationary random fields obeying log-normal distribution of undrained shear strength were generated and further mapped into nonlinear finite-element analysis. Monte Carlo simulations were then performed to evaluate the bearing capacity for the selected ranges of the degree of nonstationarity and the spatial correlation length in undrained shear strength. The normalized bearing capacities derived from two different random field models for the cases of single and two footings were compared, and the effect of footing interference was also discussed. [ABSTRACT FROM AUTHOR]

Overlooking the anisotropic behavior of soil with directional shear strength parameters can lead to unrealistic estimation of the actual limit load. This research is focused on the effect of the shear strength anisotropy on the bearing capacity of surface footings near slopes. The lower bound limit analysis in conjunction with the finite element method and linear programming technique was employed to estimate the limit pressure. The Mohr-Coulomb yield function and an associated flow rule were adopted, and the soil-foundation interface was assumed rough. The limit pressure of the foundation was expressed as a function of effective dimensionless parameters, including the cohesion and internal friction angle anisotropy degrees, slope angle, and the distance from the foundation to the slope. Finally, 3D applied charts were presented to estimate the effect of the anisotropy on the bearing capacity of surface footings near soil slopes. [ABSTRACT FROM AUTHOR]

This paper investigates the bearing capacity of strip foundations resting on a cohesive-frictional soil sloping ground under both static and seismic conditions by applying the kinematic theorem of limit analysis. With the consideration of a composite collapse mechanism involving a generalized continually deforming shear zone, analytical expressions are established by incorporating the coupled influence of the soil resistance contributed by the cohesion, angle of internal friction, and self-weight of the soil mass. The loading conditions owing to inertia forces of supporting structures and the changes in the body forces of the supporting soil medium occurred during an earthquake are included in the analysis based on a pseudostatic approach. Rigorous upper-bound solutions are presented in the nondimensional form as charts and tables for the practical range of parameters that are normally encountered in the field. Additionally, by extending the concept of slope stability, a closed-form expression is proposed for computing the limiting values of horizontal seismic acceleration coefficients beyond which the sloping ground becomes unstable. The importance of the consideration of coupling effects of the soil resistance toward evaluating the static and seismic bearing capacity of foundations on the sloping ground over conventional approaches is discussed. [ABSTRACT FROM AUTHOR]

The lower bound limit theorem in conjunction with finite elements is used to quantitatively estimate the pseudostatic bearing capacity of a rough strip footing placed on geogrid-reinforced sandy soil. The objective of this study is to show how the bearing capacity of the rough strip footing will be improved in seismic prone areas by (i) laying a stronger soil layer beneath the foundation and (ii) inserting geogrid reinforcement layers in the soil stratum. Both the soil mass and the foundation are subjected to horizontal and vertical seismic acceleration. Solutions are obtained for different combinations of (a) geometrical parameters [e.g., size of reinforcement, depth of reinforcement, top (dense) layer thickness], (b) sand properties, and (c) seismic loadings. The optimum width and the critical depth of the reinforcement corresponding to different soil conditions and seismic loadings are presented in the article. It is observed that when seismic loads are applied, the reinforcements are to be placed at a shallow depth to ensure maximum benefit. Failure patterns are also drawn for a few cases. [ABSTRACT FROM AUTHOR]

Engineers often face challenges when designing foundations that are located over buried structures. This paper presents a laboratory model test investigation of the load–settlement response and the bearing capacity of a surface footing located over a conduit, buried within a soil slope. An attempt is made to explain the effect of the crest distance of the footing, burial depth, and diameter of the conduit on the load-carrying ability of the footing based on its failure mechanism. The test results show that the burial depth of the conduit is the most important parameter that affects the settlement and bearing capacity of the surface footing. To avoid any detrimental effect on the load-carrying ability of the footing, the depth of the crown of the buried conduit needs to be at least three times the width of the footing. The graphical illustrations and the developed correlations, presented in this paper, can be used by practicing engineers to ensure the stability of the footing. [ABSTRACT FROM AUTHOR]

This study employed finite element limit analysis (FELA) to investigate the influence of eccentric loads on the bearing capacity of footings above single and double continuous voids. Upper bound theorem (UB), lower bound theorem (LB), and adaptive meshing techniques were used in a parametric study to investigate the influence of some factors, including the relative distance between double voids, the depth of voids, the geometry of voids, the variation of soil shear strength, and the eccentricity of loadings on the bearing capacity of footings. The results indicated that, for the footings inclined above a single void, the bearing capacity with a void located on the same side of the eccentric load was less than that in an opposite position. In addition, the failure mechanisms were summarized and analyzed in this study. [ABSTRACT FROM AUTHOR]

Massive voids form in underground mines due to the continuous removal of valuable minerals. Backfill and pillars are commonly built into the voids to provide both local and regional support. The backfill material cannot rigidly support the upper load and acts as a secondary support systemto the pillars. Confinement effect effectively enhances the strength of the pillar; however, the lateral stress mobilized within the fill is contingent upon deformation of the roof and pillars, which act as a passive support. Without large-scale volumetric compression, the backfill has no effect on the prepeak stage of the pillar. In this case, the friction resistance of the interface between the pillar and backfill plays a key role in increasing the load capacity of the support system. This paper presents an analytical solution based on the load transfer of friction force in the interface, which involves the shear behavior of the interface, the mechanical properties of the pillar, and the pillar dimensions. Experimental results showed that the bearing capacity of the support system was strongly dependent on the interface shear parameters, lateral stress, and fill ratio. Comparisons were made between the proposed solution and experimental results. The results may represent a workable understanding of the interaction mechanism between backfill and pillars and assist in the design and optimization of underground mine support systems. [ABSTRACT FROM AUTHOR]

In the recent past, geotextile reinforcement with wraparound ends has been recommended to strengthen foundation soil to enhance the effectiveness of using the reinforcement. This study investigated the effects of reinforcement geometrical parameters-namely, land width occupied by reinforcement and lap length of the ends of reinforcement, which were not investigated in detail in the past-on the bearing capacity of the foundation soil. The soil considered was sandy in three different states of denseness, defined in terms of relative density as 50, 70, and 90%. The numerical model was developed using the typical elements in PLAXIS-3D software. The model was used to critically analyze the reinforcing mechanisms for improved bearing capacity caused by wraparound ends. The results showed that the bearing capacity increased by approximately 120% when reinforced with a geotextile reinforcement using the wraparound reinforcement technique, whereas this improvement was approximately 45% with the reinforcement only without wraparound ends. It was also found that the wraparound technique can be highly beneficial in a location of limited land width for foundation construction. [ABSTRACT FROM AUTHOR]

In the present paper, the interference effects on bearing capacity and settlement behavior of two closely spaced identical footings resting on the surface of granular fill (sand layer) of limited thickness underlain by soft clay have been studied by laboratory model tests. Three pairs of model footings with different shapes are used to study the effect of the aspect ratio of footing on footing interference. The width (B) and length (L) of the footings are selected in such a way that the aspect ratio or L:B ratio of the footings is varied as 1.0 (square), 1.5 (rectangular), and 2.0 (rectangular). Results show that the maximum interference factor for closely spaced footings on a single-layer sand bed is 40% higher in magnitude compared with the sand-clay layered soil bed or homogeneous clay bed. Furthermore, the interference factors increase with the increase in the L:B ratio of the footings. The optimum spacing ratio is independent of the L:B ratio of the footings, and it is 1.5 times the width of the footings. Based on the load-spread mechanism and the deformation of sand-clay interface, an analytical solution has been proposed to determine the bearing capacity of two closely spaced rectangular footings. [ABSTRACT FROM AUTHOR]