Bearing Capacity Of Shallow Foundations Research Articles

Evaluation of the pseudo-dynamic bearing capacity of surface footings on cohesionless soils using finite element lower bound limit analysis

ABSTRACT Design of shallow foundations subjected to dynamic loading is an important topic in the geotechnical engineering practice. In this study, an attempt has been made to evaluate the seismic bearing capacity of a strip footing founded on a soil deposit using the lower bound limit analysis method merged with the finite element formulation adopting the second-order conic programming (SOCP) approach. To this end, a well-established pseudo-dynamic loading scheme has been employed to apply the seismic loading on the surface footing. Accounting for the various conditions of the underlying soil layer, the results of the so-called ‘conventional pseudo-dynamic (CPD)’, ‘spectral pseudo-dynamic (SPD)’ and ‘modified pseudo-dynamic (MPD)’ bearing capacity analyses are compared with one another and their pseudo-static counterparts in terms of the value of parameter. The results show the notable influence of the amplification factor, the impedance factor and the site characteristics on the seismic bearing capacity of shallow foundations. In addition, the results obtained from the MPD, CPD and SPD methods are observed to bear a good agreement with each other. Moreover, the MPD approach was observed to render the most conservative seismic bearing capacity values.

Statistical and Numerical Study on the Performance of Skirted Foundations in Clayey Soil

Skirted foundation is considered as an alternative approach required for improving the bearing capacity of shallow foundations, by using structural skirts fixed to the edges of the foundation. The presence of vertical skirts at the base of footing generates a soil resistance on skirt side beneath the footing, which helps to resist sliding. For this purpose, a numerical analysis has been performed in order to explore the behavior of square and strip model footings with one and two sided skirts for different embedded ratio in soft clay. In this study, a vertical skirt depth (Ds) has been considered as the main parameter that significantly affects the bearing capacity. Finite element analysis using plaxis 3D Foundation has been performed to model the skirted foundation. This work indicated that, using structural skirts in one and two sides of footing has a paramount effect in improving the bearing capacity for both strip and square footings and a marginal precedence has been noticed for the strip once. Therefore, the results have demonstrated that the average improvement in bearing capacity in soft clay for the one and two sided skirts at skirted ratio of Ds/B=2 is 170 and 220% respectively. A derived equation has been proposed to calculate bearing capacity of skirted foundation and a feasible agreement has been obtained between the observed and there predicted test results where the coefficient of regression (R2) is found to be 90%.

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.

Influence of failure mechanism on seismic bearing capacity factors for shallow foundations near slopes

The bearing capacity of shallow foundations may decrease when located near slopes, particularly under seismic conditions. However, there is limited work that isolates the destabilising influences of seismicity and finite slope geometry on ultimate bearing capacity in terms of conventional bearing capacity factors. Herein, analytical solutions based on upper-bound kinematic limit analysis are used to isolate both the mechanism of failure and bearing capacity factors (Nc, Nγ and Nq) for shallow foundations near slopes subject to seismic action without using principles of superposition. The analytical solutions of ultimate seismic bearing capacity show good agreement and accuracy compared with numerical results. Seismic bearing capacity factors are assessed considering transitions in failure mechanism, soil properties and finite configurations of slope and footing geometry. The results presented demonstrate significant non-linearity in bearing capacity factors that have not been previously demonstrated, primarily owing to the transition in governing mechanism with geometry, shear strength or seismic loading. This study shows that the isolation of bearing capacity factors without superposition is possible considering slope and footing geometry, and is greatly influenced by the failure mechanism.

Effect of Roughness on Seismic Bearing Capacity of Shallow Foundations near Slopes Using the Lower Bound Finite Element Method

Abstract A lower bound finite element analysis in conjunction with linear programming technique was used to evaluate the effect of soil–foundation interface roughness on the seismic limit load of s...

An accessible calculation method of the bearing capacity of shallow foundations on anisotropic rock masses

Numerical modeling of the bearing capacity of foundations on rock masses having a high degree of anisotropy needs to represent, in most cases, a large number of discontinuities, thus making the numerical analysis difficult and, in most cases, unapproachable.In this research, a simplified numerical procedure by using the Discontinuity Layout Optimization method (DLO) which proves to be appropriate when studying the limit bearing capacity of foundations involving slip line formation and failure wedges is presented.A single discontinuity simplified procedure is proposed maintaining the accuracy of the full model. The isolated discontinuity is located in the proper position and has the correct slope to represent the whole family of discontinuities.DLO models using the proposed procedure can represent the different possible failure mechanisms that may occur in the rock mass. Besides, the ultimate bearing capacity of a particular case is checked against the available analytical solution.

Reliability Analysis of Circular Footing by Using GP and MPMR

Circular footings are designed to bear a load of super structures. Studies have been done on the influence of soil properties on bearing capacity of shallow foundations. The use of circular foundation is practical in geotechnical engineering. During the design of circular footing, bearing capacity of soil is taken into consideration, and cohesion (c), unit weight (γ), and angle of internal friction (ϕ) are the most variable parameters. Reliability analysis is used frequently for the design of circular footing. Most of the authors have used first order second moment methods (FOSM). However, FOSM is a time-consuming method. Drawbacks of FOSM have been overcome by genetic programming (GP), minimax probability machine regression (MPMR). This article gives a distinct analysis between the developed MPMR based FOSM and GP-based FOSM.

Assessment of the Bearing Capacity of Foundations on Rock Masses Subjected to Seismic and Seepage Loads

It is usual to adopt the seismic force acting as an additional body force, employing the pseudo-static hypothesis, when considering earthquakes in the estimation of the bearing capacity of foundations. A similar approach in seepage studies can be applied for the pore pressure’s consideration as an external force. In the present study, the bearing capacity of shallow foundations on rock masses considering the presence of the pseudo-static load was developed by applying an analytical solution for the Modified Hoek and Brown failure criterion. Calculations were performed adopting various inclinations of the load and the slope on the edge of the foundation, as well as different values of the vertical and horizontal components of the pseudo-static load. The results are presented in the form of charts to allow an affordable and immediate practical application for footing problems in the event of seismic loads or seepages. Finally, and to validate the analytical solution presented, a numerical study was developed applying the finite difference method to estimate the bearing capacity of a shallow foundation on a rock mass considering the presence of an additional horizontal force that could be caused by an earthquake or a seepage.

Impact of Dismantled Sheet Pile Vibration on Cohesive Soil Parameters

The dynamic impact of geotechnical works can affect subsoil, as well as structures and technical devices. In order to prevent hazards resulting from vibration, the monitoring of geotechnical works execution is necessary. This paper presents an analysis of the relationship between the vibration caused by pulling out the sheet pile and the variability of cohesive soil parameters. The authors present the case study of a construction site in Wroclaw (Lower Silesian Province, Poland). The sheet pile profiles were used as a temporary protection of the foundation excavation. After the underground floors were constructed, the sheet piles were pulled out from the ground using vibrating techniques. This is a typical action to recover steel profiles that can be reused. While the sheet piles were being pulled out, the cohesive soil adhered to steel surfaces. In order to analyse the impact of dismantled sheet pile vibration on the variability of soil parameters, laboratory tests of basic soil physical and mechanical properties were carried out. The results were then compared with the primary parameters of soil as specified in the geotechnical documentation, which had been made at the initial stage to determine the geotechnical conditions for the foundation of the designed building. The comparison has shown a negative effect of vibrations on soil properties, including a decrease in the strength parameters, as well as an increase in the liquidity index and compressibility. In this case, an increase in the earth pressure on the existing underground structures and a reduction of the bearing capacity of shallow foundations may occur. Therefore, the vibration monitoring during sheet pile dismantling process is also very important.

Bearing Capacity of Square Footing Resting on Layered Soil

The bearing capacity of layered soil studies was carried out with various approaches such as experimental, theoretical, numerical, and combination of them. This work is focused on the settlement and bearing capacity of shallow foundations subjected to the vertical load placed on the surface of layered soils. The experimental part was performed by manufacturing soil cubic container (570 mm x 570 mm x 570 mm). A model square footing of width 60 mm was placed at the surface of the soil bed. The relative density of sand was constant at 60%, and the clay was prepared with a density of 19.2 (kN/m3) and water content of 14.6%. PLAXIS 3D FEM was used to simulate the experimental tests and performing a parametric study. The results showed that there was a good agreement between experimental work and corresponding numerical results. The value of the bearing capacity was obtained from load-settlement curve. The bearing capacity of layered soil showed higher value for footing resting on clay over sand soil. It was found that an increase in the ultimate bearing capacity regarding the clay over sand with increasing in first layer thickness ratio; while, a decrease has been indicated for the sand over clay. The critical depth was found at H = (2-3m), and the failure pattern was not unique for layered soil.

Pseudo-static Seismic Bearing Capacity of Shallow Foundations in Unsaturated Soils Employing Limit Equilibrium Method

There exist many structures founded on unsaturated soil deposits. Shear strength augmentation due to the evolution of the matric suction within the unsaturated porous media enhances the bearing capacity of the overlying foundation. This paper presents the evaluation of the pseudo-static seismic bearing capacity of the shallow foundations resting on unsaturated soil deposits using limit equilibrium method. Adopting the Coulomb failure mechanism and Bishop effective stress concept, the bearing capacity equations are solved. The distribution of the matric suction beneath the footing is assumed to be linear. The results of the bearing capacity evaluation are validated against some experimental data found in literature for the static condition. For the seismic loading consideration, the pseudo-static method is utilized. The dual effect of the earthquake acceleration vertical component is thoroughly discussed and a suction transition point is introduced in which the minimum bearing capacity is observed to bear the same value for both upward and downward directions. The increase in the matric suction throughout the soil deposit leads to the increase in the soil shear strength, thus posing more resisting forces as well as higher ultimate bearing capacity. The offered solution is deemed a consistent and useful tool for the accurate prediction of the seismic bearing capacity of shallow footings resting on unsaturated soil deposits.

Seismic Bearing Capacity of Shallow Strip Footings on Sand Deposits with Weak Inter-layer

The main objective of this study is to evaluate the ultimate seismic bearing capacity of a shallow strip footing resting on a frictional soil stratum containing a weak intervening layer. The majority of the studies throughout the literature pertain to the static loading condition. The previous seismic analyses have also been devoted to the studies on the bearing capacity of shallow strip footings resting on a two-layered soil. The influence of weak middle layer on the pseudo-static seismic bearing capacity of shallow foundations is the main focus of the present study. To determine the seismic bearing capacity, the limit equilibrium method (LEM) was combined with the pseudo-static seismic loading approach. Bearing capacity was defined by a single equivalent coefficient which combines the contributions of cohesion, surcharge and soil weight. A two-wedge failure surface, known as the Coulomb failure mechanism, was adopted to model the slip lines in each layer to calculate the seismic bearing capacity of the overlying shallow strip footing. The Particle Swarm Optimization (PSO) algorithm was invoked to seek the optimal bearing capacity value under different strength and loading conditions. In order to verify the validity of the presented formulations, the results were compared with some Finite Elements Method (FEM) analyses available in literature. Furthermore, the influence of the embedment depth, thickness, and strength of the weak inter-layer on the seismic bearing capacity of the shallow footing is investigated in the presence of different seismic loading arrangements. The results of this study could be very helpful in the seismic analysis and design of shallow foundations overlying a soil medium containing a weak layer of various strengths.

Study of the Effect of an Inclined Bedrock on the Bearing Capacity of Shallow Foundations

In order to determine the bearing capacity of shallow foundations, most of the analytical methods take the assumption that the soil layers below the foundation are homogenous, horizontal and are extended to a great depth. However, in reality, the geological structure under the foundation is much more complex and far from simplifying taken the hypothesis. This can lead to unrealistic bearing capacity values and cause serious difficulties for the concerned structures. This paper aims to study the effect of various parameters such as soil geotechnical properties and geometrical specifications on the ultimate bearing capacity of a shallow foundation on an inclined bedrock, in order to obtain a new equation for determining the bearing capacity. A series of numerical modeling was performed to study the influence of the effective parameters of geotechnical and geometrical properties for calculation of the ultimate bearing capacity. The obtained results were verified through some laboratory small-scale models, and the failure surfaces of a shallow foundation on an inclined bedrock layer were analyzed. Finally, the verified results of the modeling were then evaluated by genetic algorithm in order to determine the new bearing capacity factors ( $$\mu_{a} , \mu_{b} , \mu_{c}$$ ) for the presented equation.

New explicit formulation for ultimate bearing capacity of shallow foundations on granular soil using M5’ model tree

Abstract Proper estimation of the ultimate bearing capacity of the shallow foundations is of vital significance as a necessary part of foundation design for different structures. This study aims at developing explicit and high-precision expressions for predicting the ultimate limit states of shallow foundations under vertical loading over a practical range of predictors including foundation width (B), foundation length (L), embedment depth (D), internal friction angle (φ) and specific gravity (γ). A more comprehensive database of the ultimate bearing capacity test results, in contrast to previous studies, were considered for modeling using the M5’ Model Tree algorithm. Predictions are compared with measurements, conventional bearing capacity theories and available soft computing approaches. Moreover, it is shown that the new model has lower uncertainty compared with other models. It is concluded that the ultimate bearing capacity of a shallow footing can be derived from power-law functions framework and also non-dimensional equations in practice.

Bearing capacity of strip footing on rock under inclined and eccentric load using the generalized Hoek-Brown criterion

The bearing capacity of shallow foundations on rocks under inclined and eccentric loads is investigated using the kinematic approach of limit analysis theory. The study focuses on evaluating the reduction of bearing capacity induced by the eccentricity and the inclination of the load with respect to the vertical direction. The generalized Hoek and Brown criterion is adopted to describe the strength properties of the rock. A failure mechanism is used to implement the kinematic approach of limit analysis. This study provides an upper bound of the bearing capacity of the strip footing. Comparisons were made between the results of this approach and those obtained using finite element limit analysis. These comparisons confirm the accuracy of the proposed approach. Finally, a parametric study was carried out, which evaluated the effects of geometric, strength and loading parameters on the bearing capacity of the strip footing.

On the deep soil mixing method in the mitigation of liquefaction-induced bearing capacity degradation of shallow foundations

ABSTRACT Bearing capacity degradation in shallow foundations due to subsoil liquefaction is not a new challenge in earthquake geotechnical engineering. Thus far, limited mitigation measures against this problem were suggested in the literature. In this paper, mitigation of liquefaction-induced bearing capacity degradation of shallow foundations using Deep Soil Mixing (DSM) method was investigated numerically. A 3D finite difference model has been developed via FLAC3D. It was explored whether liquefaction effects on static and seismic bearing capacity of shallow foundations were diminished, and may be effectively overlooked, for DSM column diameter and length and also shallow foundation width variation. It was found that an artificial non-liquefiable soil layer made by DSM method improves the seismic bearing capacity of shallow foundations remarkably. Therefore, in terms of excess pore water pressure generation decreases and bearing capacity ratio increases. It was also concluded that by increasing the diameter and length of the DSM columns, the seismic bearing capacity of shallow foundations increases. However, as shallow foundation width increases, along with an increase in DSM column diameter and length, the performance of DSM columns and accordingly shallow foundation decreases.

Bearing capacity of foundations on rock slopes intersected by non-persistent discontinuity

Rocks encountered in foundations of heavy structures are invariably intersected by discontinuities (joints). In the past, several studies have been performed by researchers to incorporate the effect of fully persistent joints in the assessment of the load-carrying capacity of rocks. However, in the field, the joints are non-persistent, and an assumption of full persistency will underestimate the capacity. Recently, Shaunik & Singh have studied the influence of non-persistency, number of joint segments and discontinuity orientation on the strength behaviour of rock specimens (Shaunik and Singh, 2019). Bell’s approach can be used to obtain the bearing capacity of shallow foundations placed in jointed rocks. In the present study, results of the experimental work (Shaunik and Singh, 2019) conducted by Shaunik & Singh have been used to suggest expressions by extending Bell’s approach for computing bearing capacity of the foundation placed near the crown of a rock slope. Easy to use design charts are also presented for field application. Finally, a real-life problem from Indian Garhwal Himalayas is considered, and the approach suggested in this study is utilised to obtain the bearing capacity of a bridge foundation as a function of uniaxial compressive strength (UCS) of intact rock, joint friction, spacing and orientation of joint, non-persistency and number of joint segments.

Bearing capacity of shallow foundation under cyclic load on cohesive soil

Abstract The bearing capacity of shallow foundations under static loads has been widely studied by various authors. In contrast, the bearing capacity under dynamic loads has been solved indirectly by adopting an equivalent pseudostatic approach or by means of reduction coefficients. The study of the problems related to cyclic loads has focused mainly on the behavior of granular soils. However, in the case of cohesive soils, these began to be studied in detail as a result of the Northridge, Kocaeli and Chi-Chi earthquakes that took place in the 90s. The object of the present work is to evaluate the influence of pore pressure in the calculation of bearing capacity of shallow foundation on cohesive soil and dynamically requested. This research is based on the results of cyclic simple shear tests carried out with samples from the Prat port (Barcelona). A pore-water pressure generation equation is proposed that depends on the effective vertical stress “in situ” (σ’ov), static shear stress (τo), cyclic shear stress (τc), and void ratio (e0). The formulation was implemented to the finite difference software FLAC2D, by which the bearing capacity of foundations can be determined. The proposed formulation can calculate the maximum cyclic load (CL) that a cohesive soil can resist before failure by cyclic softening, as a consequence of cyclic loads transferred by a shallow foundation. The practical application of this research is to provide a chart to calculate the bearing capacity of cohesive soils requested by cyclic loading (CL). This application takes into account the properties of the ground, the static load capacity (Phe) and the effective load outside the foundation ( q ). In addition, the formulation is validated in the application of a real case.

Experimental Study of the Effects of Bedrock on the Square Skirted Shallow Foundations Behavior

In this paper, the effect of existence of a bedrock on the behavior of a square shallow foundation was explored. A series of experimental small scaled laboratory tests were carried out to study the effects of some parameters of skirt length and the depth of a bedrock on a square shallow foundation bearing capacity, displacement and behavior which has been subjected to vertical loading. In this case, sandy soils in different relative densities for the cases of loose, medium and dense were used as the soil layer. Also, to study the results of a rigid base layer, a comparison study was conducted on the laboratory results in two cases of with and without attendance of the bedrock. The results show a linear growth in ultimate bearing capacity ratio in variation of depth of the bedrock layer corresponding to different skirt length, while the increment rates are different in different soil relative density and for some cases the effect of the bedrock is insignificant.

Bearing Capacity of Shallow Foundations on Unsaturated Soils: Analytical Approach with 3D Numerical Simulations and Experimental Validations

AbstractThe ultimate bearing capacity of shallow foundations on unsaturated soils is investigated through the concept of suction-dependent effective stress. The first approach is a new analytical s...