Ultimate Bearing Capacity Of Footings Research Articles

Ultimate bearing capacity of strip footings on Hoek-Brown rock slopes – A stress characteristics solution

The present study addresses the ultimate bearing capacity of strip footings on rock slopes under seismic conditions. The stress characteristics method (SCM) is combined with the modified pseudo-dynamic (MPD) approach for the intended purpose. Unlike the solutions available in the literature, the generation of the stress characteristics network within the framework of the SCM automates the potential failure mechanism of the slope medium at the limiting state of collapse. The MPD approach enables the analysis to capture realistic earthquake inertia forces induced in the slope, considering the material damping properties of the slope. The non-linear nature of the rock mass strength is captured using the generalized Hoek-Brown failure criterion. The seismic ultimate bearing capacity of strip footings is reported as non-dimensional charts. Additionally, the impact of relevant dynamic characteristics of seismic waves and rock mass properties is thoroughly assessed by conducting a detailed parametric investigation. The results reveal a substantial reduction in the ultimate bearing capacity of footings resting on rock slopes under earthquake conditions. The efficacy of the proposed methodology is validated with the existing solutions reported by various researchers.

Experimental and numerical study for seismic response of strip footing on slopes

The present study investigates the free-field response of slopes as well as the seismic response of strip footing on slopes. The small-scaled physical model tests (PMT) have been performed under one-directional excitation. The sinusoidal waves of different amplitudes and frequencies are applied at the base of the model. To examine the kinematic interaction between the footing and slope, a rigid strip footing is placed at the center of the slope. The free-field response of the slope as well as the seismic response of the footing on the slope from PMT is determined using digital image correlation (DIC). Two-dimensional finite element analysis (FEA) has been carried out to simulate the PMT results. No study has been reported in the literature considering both experimental and numerical work. Further, the effects of increasing load on the footing on slopes have not been examined yet. Results from PMT and FEA are found in good agreement. The maximum amplification is observed near the crest for free-field response of slope. For both horizontal ground surface and sloping ground, the maximum amplification occurs at the frequency of excitation. However, some small peaks at other frequencies are also observed for the sloping ground due to the reflection of waves from the sloping surface. The seismic settlement of strip footing is increased with the increase of slope angle, amplitude and frequency of the excitation. However, the seismic settlement decreases with the increase in footing width and edge distance of footing from the slope. For footing on slope, the maximum amplification is observed at the center of the slope. A large settlement of footing is observed when the footing is heavily loaded (e.g., 80% of the ultimate bearing capacity of footing).

Performance of two-tiered reinforced-soil retaining walls under strip footing load

In the current study, an attempt was made to investigate the performance of two-tiered mechanically stabilized earth walls (T-TMSEWs) under static footing loading using reduced-scale model tests. For this purpose, twenty-four T-TMSEW models were constructed with three different types of reinforcement (metal strips, geogrid and geostraps) and were loaded using the rotatable and non-rotatable strip footings in different distances to the wall crest. Findings indicated that, although decreasing the reinforcement stiffness and the soil-reinforcement interaction reduces the ultimate bearing capacity of footings, the use of extensible reinforcements with low pull-out capacity and allowing the footing to tilt can be two effective solutions in T-TMSEWs to minimize deformations of backfill surface and connection loads as well as lateral pressures. It was observed that the use of a two-tiered configuration in MSE walls and also reducing tensile stiffness and soil-reinforcement interaction simultaneously, not only lead to change in the slip surface geometry but also prevent the development of deep slip surfaces in the lower tier. On the other hand, increasing the footing distance to the wall crest in the range of reinforced zone was found to be another influential solution to improve the bearing capacity, reduce wall deformations and also minimize lateral pressures.

Influence of a Thin Horizontal Weak Layer on the Mechanical Behaviour of Shallow Foundations Resting on Sand

The presence of minor details of the ground, including soil or rock masses, occurs more frequently than what is normally believed. Thin weak layers, shear bands, and slickensided surfaces can substantially affect the behaviour of foundations, as well as that of other geostructures. In fact, they can affect the failure mechanisms, the ultimate bearing capacity of footings, and the safety factor of the geotechnical system. In this research, numerically conducted through Finite Element Code Plaxis 2D, the influence of a horizontal thin weak layer on the mechanical behaviour of shallow footings was evaluated. The obtained results prove that the weak layer strongly influences both the failure mechanism and the ultimate bearing capacity if its depth is lower than two to four times the footing width. In fact, under these circumstances, the failure mechanisms are always mixtilinear in shape because the shear strains largely develop on the weak layer. However, the reduction in the ultimate bearing capacity is a function of the difference between the shear strength of the foundation soil and the layer. The presence of a thin weak layer decreases the ultimate bearing capacity up to 90%. In conclusion, this research suggests that particular attention must be paid during detailed ground investigations to find thin weak layers. Based on the obtained results, it is convenient to increase the soil volume investigation to a depth equal to four times the width of the foundation.

Bearing capacity of surface circular footings on granular material under low gravity fields

Low gravity fields have been simulated through magnetic acceleration to conduct experimental study on bearing capacity of circular footings on a type of crushable planetary regolith simulant, which has comparable density and particle size distribution of lunar soil. The load–settlement responses of surface spread footings are obtained by investigating the relative density, footing size and gravity effects. Applying the hyperbolic asymptote method, normalised foundation stiffness and ultimate bearing capacity are obtained by curve fitting and predicted by power functions using multivariate nonlinear regression. The results show that the nonlinear gravity effect is not negligible, related to stress condition, soil dilatancy and mobilised friction angle. A cone penetration test (CPT)-based method for prediction of bearing capacity is proposed with correlations between ultimate bearing capacity of footings and shallow penetration stiffness of CPTs, avoiding the uncertainties of soil property estimations. Analyses of allowable bearing capacity and footing influence zone in consideration of footing size and gravity effects could therefore improve the design of shallow foundations on the Moon and Mars, and provide new understandings and potential implications to the bearing capacity of shallow foundations on crushable granular material in both terrestrial and extraterrestrial geotechnical engineering.

Ultimate bearing capacity of eccentrically loaded strip footings above voids in rock masses

Based on a self-developed adaptive finite element limit analysis (AFELA) code and generalized Hoek-Brown (GHB) failure criterion, the footing-void system subjected to eccentric load in rock masses is investigated. The research emphasis of this study is on quantifying the effect of the load eccentricity and voids on the ultimate bearing capacity of footings. Predictions of footing ultimate bearing capacity can be captured by the scope enclosed by upper bound (UB) results and lower bound (LB) results within 5% relative errors. All of independent variables including the void location, the void size, the void length-width ratio and the rock strength parameters are involved in parametric study in pairs. Furthermore, typical failure patterns which can cover nearly all cases are discussed for deeper insight into how the stability evolving with variations of above-mentioned variables.

Eccentric bearing capacity of embedded strip footings placed on slopes

The bearing capacity of strip footings placed on slopes is determined by slope geometry, soil strength and foundation distribution. Previous analyses for the ultimate bearing capacity of footings placed on slopes mainly focus on the fist two factors, and the influence of embedded soils and eccentric surcharges is rarely discussed. In this study, the eccentric bearing capacity of embedded strip footings placed on slopes is addressed by applying the finite element limit analysis method. Effective parameters, including an embedded depth ratio and an eccentric ratio, on the bearing capacity are examined. Design charts are provided to evaluate the eccentric bearing capacity of embedded footings as a function of dimensionless parameters. In addition, the ultimate bearing capacity predicted by the finite element limit analysis method is compared with that obtained by the existing methods.

Ultimate bearing capacity of rigid footing under eccentric vertical load

In geotechnical engineering, the stability of rigid footings under eccentric vertical loads is an important issue. This is because the number of superstructure buildings has increased and the situation of structures being subjected to eccentric vertical loading is occurring more and more frequently. In this study, focus is placed on the ultimate bearing capacity of a footing against the eccentric load placed on two types of soil, namely, sandy soil and clayey soil, using a finite element analysis. For the sandy soil, the study newly introduces an interface element into the footing-soil system in order to properly evaluate the interaction between the footing and the soil, which greatly affects the failure mechanism of the footing-soil system. For the clayey soil, the study improves the analysis procedure by introducing a zero-tension analysis into the footing-soil system. Two friction conditions between the footing and the soils are considered; one models a perfectly rough condition and the other models a perfectly smooth condition. For a two-dimensional analysis of the footing-soil system, the rigid plastic finite element method (RPFEM) is applied to calculate the ultimate bearing capacity of the eccentrically loaded footing. The RPFEM is extended in this work to calculate not only the ultimate bearing capacity, but also the distribution of contact stress along the footing base. The study thoroughly investigates the effect of the eccentric vertical load on the ultimate bearing capacity in the normalized form of V/Vult and e/B where e is the length of the eccentricity and B is the width of the footing. Vult indicates the ultimate bearing capacity of the centric vertical load. The failure envelope in the plane of V/Vult and M/BVult is further investigated under various conditions for the sandy and clayey soils. M is the moment load induced by the eccentric vertical load. This study examines the applicability of the failure envelope obtained for the eccentric vertical load to the cases where two variables, V and M, are independently prescribed. The obtained results are coincident and indicate the wide applicability of the failure envelope in the normalized V-M plane in practice. Finally, in a comparison with previous researches, the numerical data in the present study lead to the derivation of new equations for the failure envelopes of both sandy and clayey soils.

ASSESSING THE ULTIMATE BEARING CAPACITY OF FOOTING IN A TWO-LAYERED CLAYEY SOIL SYSTEM USING THE RIGID PLASTIC FINITE ELEMENT METHOD

Ultimate bearing capacity formulae for foundations are specified in the guideline published by the Architectural Institute of Japan for the design of building foundations. The rigid plastic finite element method was developed by Tamura and Ohtsuka to estimate the ultimate bearing capacity of footing. Unlike deformation analysis, this method employs limited soil constants; it uses only the strength parameters of cohesion c and friction angle φ as it considers the limit state directly and disregards the deformation of the building and ground. A series of rigid plastic finite element analyses were conducted to compare the ultimate vertical and inclined bearing capacities of spread foundations between the simulation results and the theoretical formula for a two-layered clayey soil system. The change in the failure mode of the ground was discussed using the geometrical ratio between the width of the footing and the height of the surface layer. The strength ratio of the surface and second ground layer was clearly shown to affect the formation of failure mode. The applicability of the rigid plastic finite element method for the assessment of the ultimate bearing capacity of a two-layered clayey soil system was successfully demonstrated.

ULTIMATE VERTICAL BEARING CAPACITY OF CLAYEY SQUEEZE BREAKDOWN USING RIGID-PLASTIC FINITE ELEMENT METHOD

The relations of ultimate bearing capacity for foundations are specified in the guideline published by the Architectural Institute of Japan for design of building foundations. The rigid-plastic finite element method developed by Tamura and Ohtsuka has been employed to estimate the ultimate bearing capacity of footings. The characteristic of this method is that, in contrast to deformation analysis, it applies limited soil constants; only the strength parameters, such as cohesion and friction angle, are used since the method deals with the limit state directly by disregarding the deformation of the building and ground. In this study, a series of rigid plastic finite element analyses were performed to compare the ultimate bearing capacities of spread foundation for clayey squeeze breakdown obtained by simulations and the formulae of the Architectural Institute of Japan. The change in the failure mode of the ground was discussed considering the geometrical ratio between the width of the footing and the surface clay layer. In addition, inclined load was considered for clayey squeeze breakdown. The applicability of rigid plastic FEM to the assessment of ultimate vertical bearing capacity of clayey squeeze breakdown was demonstrated.

Effective Width Rule in the Analysis of Footing on Reinforced Sand Slope

Abstract This paper presents the results obtained from an experimental programme and numerical investigations conducted on model tests of strip footing resting on reinforced and unreinforced sand slopes. The study focused on the determination of ultimate bearing capacity of strip footing subjected to eccentric load located either towards or opposite to the slope facing. Strip footing models were tested under different eccentricities of vertical load. The obtained results from tests conducted on unreinforced sand slope showed that the increase in eccentricity of applied load towards the slope facing decreases the ultimate bearing capacity of footing. Predictions of the ultimate bearing capacity obtained by the effective width rule are in good agreement with those proposed from the consideration of total width of footing subjected to eccentric load. The ultimate bearing capacity of an eccentrically loaded footing on a reinforced sand slope can be derived from that of axially loaded footing resting on horizontal sand ground when adopting the effective width rule and the coefficient of reduction due to the slope. When increasing the distance between the footing border to the slope crest, for unreinforced and reinforced ground slope by geogrids, the ultimate bearing capacity of footing is no more affected by the slope ground.

Pseudo-Static Bearing Capacity Analysis of Shallow Strip Footing over Two-Layered Soil Considering Punching Shear Failure

In present analysis, ultimate bearing capacity of footings residing on sub soils comprising of two layers has been investigated for the event of a thin soil layer overlying a weak deposit. Pseudo-static approach has been applied to find out the ultimate bearing capacity of shallow strip footing resting on two layered soil. Ultimate bearing capacity equation was derived as a function of the properties of soils, the footing width and the top soil thickness. Particle swarm optimization algorithm is used to optimize the solution using MATLAB R2009. The paper acquaints a detailed parametric study of the design parameters including the effect of angle of friction, mobilization factor, the ratio of the depth of embedment to the footing width and the ratio of the cohesions of both the layers. Design charts were developed in dimensionless form for very wide range of design parameters. Comparative study of the present analysis has been applied with respect to different analytical, numerical and experimental studies.

Finite element investigation and ANN-based prediction of the bearing capacity of strip footings resting on sloping ground

Footings placed on or near a slope, the slope face act as a finite boundary that leads to an inappropriate and inadequate development of the plastic region of failure as the foundation approaches the limit state under the applied loading. Depending upon the position of the footing and steepness of the slope, the above-mentioned phenomena might lead to considerable decrease in the bearing capacity of the foundation. A sequence of finite element analysis has been carried out using Plaxis 2D v2015.02 to inspect the ultimate bearing capacity of strip footings placed at the crest of the c–φ soil slope. The effect of various geo-parameters namely internal angle of friction (φ), cohesion (c), setback distance (b), width of footing (B), slope angle (β) and embedment depth of footing (Df) on the ultimate bearing capacity of the footing have been investigated and the outputs obtained are appropriately elucidated. In addition, large database of numerically simulated ultimate bearing capacity has been considered to develop and verify the ANN model to establish the relative importance of the input parameters.

Estimation of Ultimate Bearing Capacity of Footings on Soft Clay from Plate Load Test Data Considering Variability

The ultimate bearing capacity of a foundation can be determined from the load–settlement response obtained from plate load tests. For clayey soil it is known that the ultimate bearing capacity of footing is equal to that of a test plate. However, the present study shows that it varies with the variation of type of loading, size and shape of test plate and soil consistency. For reaction type of loading, the load is observed as normally distributed random variable with an average co-efficient of variation of 0.018. For different shape and size of plates, the bearing pressure–settlement curves show a high degree of variation. Subsequently the bearing pressures and settlements are normalized to dimensionless parameters and the normalized plot shows a reduction in variability. Further, the normalized curves are fitted to the hyperbolic model by nonlinear regression with non-constant variance. The model parameters, their standard errors, 95% confidence intervals and co-efficient of determination are quantified. The horizontal asymptote of the hyperbolic model has been used to estimate the ultimate bearing capacity. This method yields a value very close to other conventional bearing capacity methods. A sensitivity analysis shows the influence of various parameters on the bearing pressure.

Experimental and Numerical Study of Bearing Capacity and Effect of Specimen Size on Uniform Sand with Medium Density, Reinforced with Nonwoven Geotextile

Reinforced soil is a composite material in which elements of high tensile resistance are implemented to increase the tensile resistance of the soil. Geotextiles are one of the major groups of geosynthetic products that are used for soil reinforcement. This paper deals with the effects of using nonwoven geotextile to improve the ultimate bearing capacity of footings resting on sand with medium density. The plate load tests were performed using 27 cm × 27 cm and 35 cm × 35 cm square plates, and the effects of the depth of the first layer of geotextile, vertical spacing as well as the number of geotextile layers on the ultimate bearing capacity of the footings were studied. Moreover, the impact of plate size and sample size was examined numerically by performing 3-D finite element analyses with different sizes of the square plate. The experimental results showed that the maximum bearing capacity is achieved for the system with four geotextile layers, vertical spacing of 0.3B between geotextile layers and geotextile width of 4B, where B is the width of the plate. The numerical analyses indicated that with increasing the size of the plate up to 65 cm, the values of the bearing capacity ratio (BCR) gradually decrease; however, additional increase in the size of the plate has a little impact on BCR values.

Behavior of Shallow Strip Footing on Twin Voids

This paper numerically examines the bearing capacity and failure mechanism of a shallow strip foundation constructed above twin voids. The voids may refer to caves, caverns, underground aqueduct or tunnels due to water seepage, chemical reaction or deliberately excavated in soil deposit. The ability of numerical model to accurately predict the system behavior is evaluated by performing verification analyses on existing researches. Subsequently, a parametric study carried out to reveal the influence of size of footing/voids and their location (i.e. depth, spacing, eccentricity) on the bearing capacity of footing. To clarify the failure mechanism, the distribution of shear strain in the soil for different scenarios is assessed. The parametric study provided a new framework to determine the bearing capacity and the mode of failure for footings on voids. Based on the results, a criterion can be issued to avoid collapse of footing/voids regarding the shape, location and size of voids. The results can also be used to design construction of a footing on existing voids while the acquired failure mechanisms can be appointed to develop analytical solutions for this problem. Results demonstrated that a critical depth for voids and a critical distance between them exist where the influence on the ultimate bearing capacity of footing disappears.

Behavior of strip footing on fiber-reinforced cemented sand adjacent to sheet pile wall

In urban areas, shallow foundations are often placed along the ground surface above a sheet pile wall. In this research, the potential benefits of reinforcing the active zone behind a model sheet pile wall by using polypropylene fiber and cement kiln dust have been investigated experimentally and numerically. Tests were conducted by varying parameters including fiber ratio (RF), cement kiln dust (CKD) ratio, thickness of reinforced layer, footing location relative to the sheet pile wall and curing time of reinforced layer. Finite element computer code PLAXIS 2D foundation was used for numerical modeling. Close agreement between the experimental and numerical results was observed (maximum difference 14%). Experimental and numerical results clearly show that fiber insertion into the cemented soil causes an increase in ultimate bearing capacity of footing and significant reduction in the lateral deflection of the sheet pile wall. At higher fiber ratios (RF ≥ 0.75%), the bearing capacity ratio (BCR) increased by about 42% and the effect of CKD ratio on BCR is more pronounced. The addition of fibers changed the brittle behavior of cemented sand to a more ductile one. Critical values of reinforcing parameters for maximum reinforcing effects are established.

The Bearing Capacity of Footings near Slope Considering the Footing-Soil Interaction

In some cases, structures are built on or near aslope. The ultimate bearing capacity of the foundations for these structures issignificantly affected by the presence of the slope. In this paper, the ultimate bearing capacity of footings near slopes is investigated by the finiteelement method. Consideration is given to the effect of slope angle, height ofslope, the distance from the edge of the slope to the footing, soil propertiesand the interaction between the soil and footing. Conclusions are drawn: Ingeneral, the dimensionless bearing capacity qu/γB increases with theincrease of the ratio cu/γB, the increase of L/B, and decrease ofthe slope angle β. Thecurves describing the relationship between cu/γB and qu/γBcan be characterized using three main properties, namely a linear section, anon-linear section, and zero bearing capacity point. Within the linear section,local bearing capacity failure contained to within the face of the slope; theheight of the slope does not influence the bearing capacity. In the non-linearsection, the curves of the relation (cu/γB, qu/γB) isgoverned by overall slope failure.

A Multiple Regression Equation for Prediction of Bearing Capacity of Geosynthetic Reinforced Sand Beds

Several researchers have studied the effects of various important parameters like number of layers of reinforcement (N), depth of the upper most layer of reinforcement from the base of the footing (u), spacing of the reinforcement layers (h), width of reinforcement layer (b), tensile strength of reinforcement (T) and density of soil (γ) on the ultimate bearing capacity of footings on reinforced soils. However, very few of them have attempted to develop equations to estimate the bearing capacity of the footings on reinforced soils by considering all the above parameters. Review of the existing state of the art in this area is presented in this paper and the ability of the existing analytical models to predict the ultimate bearing capacity of reinforced sand beds is verified using results from laboratory model tests. A multiple regression equation to estimate the ultimate bearing capacity of square footing resting on geosynthetic reinforced sand beds based on the laboratory model studies is presented. This equation is verified against the experimental results of model studies and also with the experimental measurements of other researchers. Statistical analysis of the model test data revealed that the aperture size of the reinforcement is very influential in altering the bearing capacity of reinforced sand beds. The regression equation developed in this study is reasonably good in predicting the bearing capacity of square footing on dense sand reinforced with planar geosynthetics.

剛塑性有限要素法を用いた根入れ基礎の支持力解析

The ultimate bearing capacity formula of embedded foundation is specified in the guideline published by the Architectural Institute of Japan for design of building foundation. The rigid plastic finite element method was developed by Tamura and Ohtsuka to estimate the ultimate bearing capacity of footing. The characteristic of this method is to employ few strength parameters. It does not use the Poisson’s ratio and the elastic modulus since it directly deals with the limit state by disregarding the elastic deformation of building and ground. The strength parameters as cohesion, c and internal friction angle, φ are only employed. By performing a series of rigid plastic finite element analyses, the comparison of ultimate bearing capacity of embedded foundation was conducted between the formula of the Architectural Institute of Japan and the simulation results. On the dispersion failure mode of ground, the bearing capacity of penetration foundation was made clear by the width and the penetration length of foundation and the strength ratio of first and second layers of two layered ground.