Ultimate Bearing Capacity Of Foundation Research Articles

Bearing Capacity Factor of Shallow Foundation on Reinforced Sloped Clayey Soil

The placement of buildings and structures on/or adjacent to slopes is possible, but this poses a danger to the structure due to failures that occur in slopes. Therefore, a solution or improvement should be determined for these issues of the collapse of the structure as a result of the failure of the slopes. A laboratory model has been built to test the impact of some variables on the bearing capacity factor. The variables include the magnitude of static axial load applied at the center of footing, the depth of embedment, the spacing between geogrid reinforcement layer and the numbering of the geogrid sheet under the footing, the inclination angle of slope clayey soil (β), the spacing between the footing's edge and the slope's end (b/H). The results show that the critical case of reduction in bearing capacity is mobilized at (b/H˂ 0.25) and (β˃ 30°). A design chart has been obtained to the case of unreinforced slope soil under a footing to describe the reduction in (Nc) when increasing the inclination angle and another design chart of the case of reinforced slope soil with (N=1, 2 and 3) has been obtained to show the increase in value of (Nc) with increasing the number of the reinforced layer at different values of (β) and finally simple equations have been obtained in order to calculate the ultimate bearing capacity of foundation on sloped clayey soil at different number of reinforcement.

Analysis of foundation bearing capacity and structural stability of suction bucket for offshore wind power

The large-scale wide and shallow bucket foundation of offshore wind power has a unique bucket top bearing mode, and the bucket foundation is provided with partition plates, which has greater bearing capacity as a whole. By numerical method, the solid and structural elements such as bucket body, rib plate connector and silo plate, as well as bucket-soil contact element are established, and the real three-dimensional complex model of bucket foundation and foundation soil is constructed in detail. The nonlinear contact calculation of bucket foundation under the combined loading modes such as horizontal load, wave force, vertical load and bending moment are simulated, and the deformation, bearing characteristics and safety of suction bucket are analyzed. The ultimate bearing capacity of foundation under horizontal load, vertical load and bending moment are calculated by Flac3d finite difference method, which provide reference for the foundation structure selection, bucket foundation design, implementation and safety evaluation of offshore wind farm projects.

Bearing Capacity of Circular Foundation on Sand Layer of Limited Thickness Underlain by Rigid Rough Base Subjected to Eccentrically Inclined Load

Abstract Laboratory model test results for the ultimate bearing capacity of a shallow rough circular surface foundation over a sand layer of limited thickness underlain by a rigid rough base subjected to an eccentrically inclined load have been presented. The sand layer for tests was prepared at a relative density (Dr) of 69 % using five different thicknesses, H. Tests were conducted at H/B values of 0.3, 0.5, 1, 2, and 3 (B = diameter of foundation). The load eccentricity ratio e/B varied from 0 to 0.15, and the load inclination with the vertical (α) was changed from 0° to 20° in 5° increment. Based on the model test result, a reduction factor has been proposed that can be used to estimate the ultimate eccentrically inclined load per unit area of the foundation supported by a sand layer of limited thickness, from the ultimate bearing capacity of a foundation on a sand layer extending to a great depth under an eccentrically inclined load.

Discussion of the Method to Determine the Ultimate Bearing Capacity of Soil Foundation

Combining literature examples, this paper has carried out Contrastive analysis of the theoretical formula method and finite element method about the ultimate bearing capacity of foundation, To verify rationality and superiority of the incremental load method in finite element ABAQUS in solving the bearing capacity of foundation soil. The study can provide certain reference for practical engineering calculation and analysis of foundation bearing capacity.

Finite Element Investigation of the Bearing Capacity of Square Footings Resting on Sloping Ground

The ultimate bearing capacity of foundation placed on a slope is significantly affected by its vicinity to the slope face, which offers substantially lesser passive resistance as compared to a footing resting on a semi-infinite medium. Conventional bearing capacity theories fail to address the behavior of such foundations. Few existing theories predict the bearing capacity of foundations on slopes considering stress-based failure approach. However, deformation along the slope plays a major role in governing the failure of such foundations, thus requiring a coupled stress-deformation based failure analysis. With the aid of 3-D finite element modelling, employing coupled stress-deformation analysis, this study addresses the failure mechanism and the bearing capacity (q u ) of a square footing located on a dry cohesionless slope. The effect of various parameters, namely the angle of internal friction of soil, setback distance, slope inclination, footing width and the depth of embedment of the footing, have been investigated. Variations parameters are found to noticeably alter the bearing capacity estimate and the observed failure mechanism. A critical setback distance is obtained [(b/B)critical = 3] beyond which the failure mechanism resembles the same obtained for a footing resting on horizontal ground. The unit weight and modulus of elasticity of the soil material is found to have negligible effect on the bearing capacity.

Behavior of Piled Raft Foundation Model Embedded within a Gypseous Soil Before and after Soaking

The paper explain an experimental study to show piled raft system behavior when embedded within gypseous soil in three different stats (dry, socking for 1 day and placing a bearing layer of dense sand below the gypseous soil when socking for 1 day). A small-scale “prototype” model of steel box with dimension of (60cm length x 60cm width x 75cm heights) was used for carried out the model tests. Two different lengths of reinforced concrete pile models (40cm and 45cm) of 2.0cm dia. were used to keep the same imbedded length ratio during testing piled raft and piles only. Three different configurations of pile groups (single, three and six piles) were tested in the laboratory in two ways, first; the raft does not contact with the soil and the second; the raft is in contact with the soil. In dry state, the gypseous soil showed a very high carrying capacity with reduction in settlement. Piled raft foundations show an efficient in dry state, where the load carrying capacity increased and the settlement decreased. The improvement ratios in the load carrying capacity were about 16% for single piled raft and 39% for group of three-piled raft, while settlement reduction ratios were about 18% for single piled raft and 45% for group of six-piled raft. When the gypseous soil socked with water for 1 day, the ultimate bearing capacity of foundations is generally reduced by about (69%-83%) compared with dry state for all model configurations. The improvement ratios in ultimate bearing capacity due to using piled raft in soaking state was about (11% -50%) whilst the reduction settlement ratios was about (16% -44%).

Comparison Analysis of Bearing Capacity Approaches for the Strip Footing on Layered Soils

The ultimate bearing capacity of shallow foundations is mostly based on the simplified idea that bearing layer is infinite and homogenous. However, in practice multilayered soils are mainly being used. Determination of reliable ultimate bearing capacity of foundation in multilayer soil stratum is required in the safety assessment and design analysis of a foundation structure. In present study, large number experimental, limit equilibrium, finite element analyses are performed. It has been found that a number of factors may influence bearing capacity of the soil, such as soil layer thickness, soil properties, applied stress, and type of design analysis which is not taken into consideration in the traditional bearing capacity theories. Such simplification causes structural design that is more conservative. In this study, ultimate bearing capacity of layered soil is investigated according to different conventional and recently developed techniques including finite element model, limit equilibrium methods, and experimental assessment. It is also found that the critical h / B point (first layer thickness to the foundation width) from analytical, numerical, and experimental methods are equal to 2.0, 2.5, and 1.5, respectively.

Recent developments on bearing capacity of strip foundation on granular soil under eccentrically inclined load

Bearing capacity of shallow foundations is one of the most important areas of study in geotechnical engineering. Since the founding work of Terzaghi (1943), results of several theoretical and experimental investigations have been published. Most of these studies relate to the case where the foundation is subjected to centric vertical load. In the present paper, an attempt has been made to summarize the important developments related to the estimation of the ultimate bearing capacity of a shallow strip foundation on granular soil subjected to eccentrically inclined loading. Reduction factors to estimate the ultimate bearing capacity of foundations have been discussed.

Observations on Load and Strength Factors in Bearing Capacity Analysis

AbstractThe widely differing factors of safety obtained by strength reduction and load increase in the ultimate bearing capacity of foundations have been reexamined analytically. In most cases, factors of safety based on load increase need to be higher than those based on strength reduction to achieve the same level of safety in design. The greater sensitivity of foundation systems to strength reduction over load increase may impact the choice of factors in ultimate limit state design.

Failure Mechanism and Bearing Capacity of Footings Buried at Various Depths in Spatially Random Soil

Abstract The objective of this paper is to demonstrate how the spatial variability of random soil affects the failure mechanism and the ultimate bearing capacity of foundations buried at various depths. A nonlinear finite-element analysis combined with random field theory is employed to explore the vertical capacity of foundations embedded at different depths in random soil. Different possibilities of shear failures resulting from spatial patterns of soil are demonstrated and are used to explain the significant discrepancy between the bearing capacity of the random soil and that of uniform soil. The effect of the spatial pattern of the soil on the development of shear planes is also investigated, with the coefficients of variation for the bearing capacity demonstrated to be closely related to the shear plane length. The results of the statistical variation in the bearing capacity are provided for different embedment depths, and these are also reported as the failure probability of the footing compared wit...

Ultimate bearing capacity of a foundation reinforced by columns or cross trenches under inclined loads: a homogenization approach

SummaryThis paper addresses the geotechnical engineering problem of evaluating the ultimate bearing capacity of a strip foundation resting upon a reinforced soil, by means of the yield design homogenization approach. The analysis is notably focused on the determination of the macroscopic strength criterion of such reinforced soils, where both constituents are purely cohesive, which can be conveniently expressed through the notion of anisotropic cohesion. A comprehensive comparison is made between the classical configuration of reinforcing columns and the more original one of orthogonal reinforcing trenches. Among the most outstanding results of the analysis is the conclusion that the cross trench configuration is notably more efficient in terms of load bearing capacity than the reinforcement by columns, notably when significantly inclined loading is concerned. Copyright © 2014 John Wiley & Sons, Ltd.

Liquefaction Mechanisms and Mitigation-A Review

It is aimed to review a series of the research investigation on liquefaction mechanism for mitigation. A number of theoretical and computational studies have been performed by various researchers to determine the different types of liquefaction mechanism and evaluating ultimate bearing capacity of foundations in the presence of the static, dynamic and blast pore water pressure. But never these mechanisms have been compared base on latest scientific achievement. The liquefaction mechanisms of soil foundation under different condition have been reviewed by comparing experimental and numerical modeling for better interpretation. The result has been highlighted that the water pressure function could be controlled without reducing pore water pressure magnitude. This guideline could be used for liquefaction mitigation. The research requirement is also recommended.

Ultimate bearing capacity of shallow strip foundation under eccentrically inclined load, Part I

Results of laboratory model tests to determine the ultimate bearing capacity of shallow strip foundation supported by sand and subjected to eccentrically inclined load are presented. The tests were conducted in dense and medium dense sands. The embedment ratio (ratio of the depth of embedment <i>D_f</i> to the width of the foundation <i>B</i>) was varied from zero to one. The load eccentricity <i>e</i> was varied from zero to 0.15<i>B</i> as well as the load inclination from zero to 20 degrees. Based on the results of the present study, an empirical nondimensional reduction factor has been developed. This reduction factor is the ratio of the ultimate bearing capacity of the foundation subjected to an eccentrically inclined load to the ultimate bearing capacity of the foundation subjected to a centric vertical load.

Numerical Analysis of Ultimate Bearing Capacity of Embedded Foundation

Soil is divided for finding the ultimate bearing capacity of foundation with given buried depth and size. Supposing a uniform load acts on the foundation, Mindlin’s integral formula and corner points method are used to get extra stress of every mesh knot by MATLAB program, then the principal stress is found. Combining with failure criterion, MATLAB program is used to find coordinates of points which are destroyed. Using graphic processing function of MATLAB, the failure points are showed in the coordinate. Increasing the rectangular uniform load, the failure points are found until these points can form a continuous failure surface. This rectangular load is the ultimate bearing capacity of the foundation. The method can avoid errors brought by unreasonable hypotheses of the empirical formulas; and the three-dimensional failure surface of the foundation soil is obtained.

Upper Bound Solution for Ultimate Bearing Capacity of Foundation Based on Unified Strength Theory

Based on unified strength theory, an upper bound solution for bearing capacity of foundation is established considering the strength of soil above the basement by using Prandtl slip model. The proposed method could be degenerated to classical slip-line method in some certain situations. A series of results could be presented by means of changing the parameters of unified strength theory. The results obtained by this proposed method are greater than those by Terzaghi method, which is mainly because the positive effects of soil strength above foundation base. Since unified strength theory could be simplified to Mohr-Coulomb strength theory in a certain situation, the results are close to those obtained by Meyerhof method. This proposed solution can consider the effects of intermediate principal stress so that we can make full use of the potential capacity of soil, which is a rigorous upper-bound solution. Other solutions are special cases of this proposed solution.

Upper Bound Solution for Ultimate Bearing Capacity of Foundation Based on Unified Strength Theory

Based on unified strength theory, an upper bound solution for bearing capacity of foundation is established considering the strength of soil above the basement by using Prandtl slip model. The proposed method could be degenerated to classical slip-line method in some certain situations. A series of results could be presented by means of changing the parameters of unified strength theory. The results obtained by this proposed method are greater than those by Terzaghi method, which is mainly because the positive effects of soil strength above foundation base. Since unified strength theory could be simplified to Mohr-Coulomb strength theory in a certain situation, the results are close to those obtained by Meyerhof method. This proposed solution can consider the effects of intermediate principal stress so that we can make full use of the potential capacity of soil, which is a rigorous upper-bound solution. Other solutions are special cases of this proposed solution.

Strength reduction and step-loading finite element approaches in geotechnical engineering

Abstract: The finite element limit analysis method has the advantages of both numerical and traditional limit equilibrium techniques and it is particularly useful to geotechnical engineering. This method has been developed in China, following well-accepted international procedures, to enhance understanding of stability issues in a number of geotechnical settings. Great advancements have been made in basic theory, the improvement of computational precision, and the broadening of practical applications. This paper presents the results of research on (1) the efficient design of embedded anti-slide piles, (2) the stability analysis of reservoir slopes with strength reduction theory, and (3) the determination of the ultimate bearing capacity of foundations using step-loading FEM (overloading). These three applications are evidence of the design improvements and benefits made possible in geotechnical engineering by finite element modeling.

Seismic ultimate bearing capacity of strip footings on slope

The influence of earthquake forces on ultimate bearing capacity of foundations on sloping ground was studied. A solution to seismic ultimate bearing capacity of strip footings on slope was obtained by utilizing pseudo-static analysis method and taking the effect of intermediate principal stress into consideration. Based on limit equilibrium theory, the formulae for computing static bearing capacity factors, N q, N c, N γ, and dynamic bearing capacity factors, N qd, N cd, N γd, which are associated with surcharge, cohesion and self-weight of soils respectively, were presented. A great number of analysis calculations were carried out to obtain the relationship curves of the static and dynamic bearing capacity factors versus various calculation parameters. The curves can serve as the practical engineering design. The calculation results also show that when the values of horizontal and vertical seismic coefficients are 0.2, the dynamic bearing capacity factors N qd, N cd and N γd, in which the effects of intermediate principal stress are taken into consideration, increase by 4%–42%, 3%–27% and 34%–57%, respectively.

Bearing capacity of foundation on slope determined by energy dissipation method and model experiments

To determine the ultimate bearing capacity of foundations on sloping ground surface in practice, energy dissipation method was used to formulate the bearing capacity as programming problem, and full-scale model experiments were investigated to analyze the performance of the soil slopes loaded by a strip footing in laboratory. The soil failure is governed by a linear Mohr-Coulomb yield criterion, and soil deformation follows an associated flow rule. Based on the energy dissipation method of plastic mechanics, a multi-wedge translational failure mechanism was employed to obtain the three bearing capacity factors related to cohesion, equivalent surcharge load and the unit gravity for various slope inclination angles. Numerical results were compared with those of the published solutions using finite element method and those of model experiments. The bearing capacity factors were presented in the form of design charts for practical use in engineering. The results show that limit analysis solutions approximate to those of model tests, and that the energy dissipation method is effective to estimate bearing capacity of soil slope.

Soil inertia effects on the bearing capacity of rectangular foundations on cohesive soils

Two kinematic mechanisms are presented, which provide an upper bound of the ultimate bearing capacity of shallow rectangular foundations resting on cohesive soil, modeled by the Tresca strength criterion. The soil-foundation interface is described by the same criterion. The foundation is subjected to an inclined/eccentric load. The horizontal component of the body force in the soil is also taken into account to discuss the effects of the soil inertia on the bearing capacity. A multi-dimensional minimization algorithm allows one to find the geometric parameters corresponding to the best upper bound solutions for different load conditions. The shape effects are discussed and the solutions are compared both with previous theoretical upper bound solutions and with experimentally based formulas, in use in engineering geotechnical practice. Finally, the detrimental effects of the soil inertia on the ultimate bearing capacity of the foundation are analysed, as a function of the shape ratio and the design safety factor.