Seismic Bearing Capacity Of Foundation Research Articles

Seismic Bearing Capacity of Strip Footings with Modified Pseudo-dynamic Method

Current research has shown a nonlinear trend in the failure of soil, and the single tangent method is commonly adopted when coping with nonlinear problems of soil failure. However, the method equates a nonlinear criterion to an optimizable linear criterion, which may differ from the actual situation, resulting in conservative results. In this paper, two types of piece-wise log-spiral failure mechanisms for bearing capacity estimations, including symmetrical and unilateral mechanisms were proposed with the nonlinear Mohr-Coulomb criterion. The static bearing capacity of foundations was evaluated using the symmetric failure mechanism, while the seismic bearing capacity of foundations was evaluated adopting a modified pseudo-dynamic method based on the unilateral failure mechanism. The result shows that the bearing capacity calculated in the paper is smaller compared to the result using the linear Mohr-Coulomb criterion. For London clay, the static bearing capacity is reduced by about 45% at a foundation width equal to 1m. From the comparisons, it is found that the proposed approach of piece-wise log-spiral failure mechanism for bearing capacity estimation is effective. In addition, parametric studies show that the nonlinear parameters, the initial factor of seismic acceleration, the normalized frequency, and the damping ratio all have obvious effects on the seismic bearing capacity. A significant reduction in the seismic bearing capacity of the foundation occurs when the normalized frequency ωsH/Vs is equal to (0.5 + n)π (n = 0, 1, 2, …). Considering that the approach proposed provides a strict upper bound to the bearing capacity, the result imparts confidence in the approach of analysis presented.

Modified pseudo-dynamic bearing capacity of reinforced soil foundations

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

Seismic bearing capacity of foundations on sloping ground using power-type yield criteria

Seismic bearing capacity of foundations on sloping ground using power-type yield criteria

Numerical analysis of evaluation of static and seismic bearing capacity of foundations on rock masses

Numerical analysis of evaluation of static and seismic bearing capacity of foundations on rock masses

Seismic Reliability Investigation of Bearing Capacity of Foundations Based on Limit Analysis and Limit Equilibrium Methods

In this paper, by considering the upper-bound limit analysis method in calculating the seismic bearing capacity of foundations, the comparison between a limit equilibrium method such as Hansen and limit analysis method in terms of reliability is investigated. Limit equilibrium has been the oldest method for performing bearing capacity of foundations. However, it seems that theoretical equations proposed by the majority of old limit equilibrium methods to calculate the bearing capacity of foundations (such as Hansen) do not consider the effects of inertial forces of the earthquake in the soil mass. These methods only take into account the horizontal load applied to the foundation and disregard the earthquake forces applied to the soil. By comparing the results of this study, it can be inferred that the reliability of the Hansen approach is very close to the limit analysis method that ignores the impact of horizontal earthquake forces applied to rigid soil blocks. Since the upper-bound limit analysis takes into account the seismic effect of inertial forces in an earthquake, its results may be considered more accurate than Hansen. This study shows that in both granular and cohesive soils in high seismicity-prone areas, usage of a more realistic method as the limit analysis is more reasonable. Considering the facility of RBD by Hansen method using EXCEL spreadsheet in comparison to the seismic reliability-based design using MATLAB programming following the upper-bound limit analysis method, graphs that offer coefficients for obtaining the equivalent value of target reliability in the limit analysis by using the Hansen formulation are presented. Additionally, this study shows that the horizontal seismic coefficient (kh) is an impressive parameter that affects the differences between the two mentioned approaches.

Seismic Pressure and Seismic Bearing Capacity of Foundations

Seismic Pressure and Seismic Bearing Capacity of Foundations

Vane Shear Footing-Integrated Rational Approach for Seismic Bearing Capacity of Foundations & Seismic Pressure

Structural buildings are subjected to huge cyclic powers during earthquakes. The structural failures during seismic events notably impact a variety of facets of buildings within tolerable levels like sustainable strength and stable energy dissipation capability to sustain inter-story drifts and overall structural damages. The major structural elements such as columns, beams and soil shearing capacities are majorly affected during seismic events. Buildings situated in the earthquake prone zone are exposed to most concerns in the structural design. Boreholes are also one of the main factors responsible for seismic waves and soil shearing. Shear strength is a term used in soil mechanics to describe the magnitude of the shear stress that soil can sustain, especially selected BC soil. The shear resistance of soil is a result of friction and interlocking of particles, and possibly cementation or bonding at particle contacts. Soils consist of individual particles that can slide and roll relative to one another. Shear strength of a soil is equal to the maximum value of shear stress that can be mobilized within a soil mass without failure taking place. In many parts of the world to avoid or control these consequences, buildings have been constructed as steel-composite structures. However, in India, buildings are being constructed as RCC framed structures. Here a novel combination of VANE shear footing and BRB method has been introduced. In this article, the effects of boreholes increase seismic bearing capacity of foundation, and load bearing capacity to balance seismic pressure.

Seismic bearing capacity of surficial foundations on sloping cohesive ground

Engineers often assume undrained conditions in stability calculations of shallow foundations resting on soil with fine content as this assumption yields conservative results. Calculation of undrained bearing capacity of shallow foundations on level ground is a well-defined problem and when the footing is located on or near slopes, empirical equations or design charts produced based on limit equilibrium, upper bound plasticity calculations or finite element method (FEM) analyses are used. On the other hand, available studies that consider seismic bearing capacity of foundations on cohesive soils do not consider the influences of all influential parameters. Therefore, their use in design practice is rather limited. Accordingly, this study attempts to develop design charts that consider the influences of all parameters that affect the undrained bearing capacity factor of surficial strip footings under seismic conditions (Ncse). These influences are footing width, slope angle, slope height, footing position, undrained shear strength and pseudo-static acceleration coefficient. As the number of parameters to be considered is high, a parametric study is conducted using FEM models. Obtained results are consistent with the results of available studies in literature. Proposed design charts allow the selection of problem specific Ncse values. A design procedure is defined and two design examples are presented for the calculation of the magnitude of undrained bearing capacity under seismic conditions.

Seismic bearing capacity of strip footing above an unsupported circular tunnel in undrained clay

By applying the lower bound theorem of limit analysis in conjunction with finite element, the bearing capacity of a strip footing located above an unlined long circular tunnel in undrained clay is computed with the inclusion of pseudo-static horizontal seismic body forces. The effects of varying the tunnel diameter and the embedment depth of tunnel below the ground level on the seismic bearing capacity of foundation are studied in detail. The design charts are provided for a wide range of pseudo-static earthquake forces. It is expected that the charts provided in this note will be quite helpful for the practicing engineers. Failure patterns are also studied in detail to understand the extent and the type of failure zone which may generate during the collapse.

Pseudo-Dynamic Bearing Capacity of Shallow Strip Footing Resting on c-Φ Soil Considering Composite Failure Surface

The evaluation of bearing capacity of shallow strip footing under seismic loading condition is an important phenomenon. This paper presents a pseudo-dynamic approach to evaluate the seismic bearing capacity of shallow strip footing resting on c-F soil using limit equilibrium method considering the composite failure mechanism. A single seismic bearing capacity coefficient (N?e) presents here for the simultaneous resistance of unit weight, surcharge and cohesion, which is more practical to simulate the failure mechanism. The effect of soil friction angle(F), soil cohesion(c), shear wave and primary wave velocity(Vs, Vp) and horizontal and vertical seismic accelerations(kh, kv) are taken into account to evaluate the seismic bearing capacity of foundation. The results obtained from the present analysis are presented in both tabular and graphical non-dimensional form. Results are thoroughly compared with the existing values in the literature and the significance of the present methodology for designing the shallow strip footing is discussed.

Pseudo-dynamic analysis for bearing capacity of foundation resting on c–Φ soil

Estimation of seismic bearing capacity of foundation in earthquake prone area is an important parameter in the design of any substructure. This paper presents a pseudo-dynamic approach for calculating the seismic bearing capacity of shallow strip footing resting on c–Φ soil using limit equilibrium method. Considering the Coulomb failure mechanism, the effect of wall friction angle and soil friction angle, soil cohesion, shear wave and primary wave velocity, and horizontal and vertical seismic accelerations are taken into account to evaluate the seismic bearing capacity of foundation. In this paper, the seismic bearing capacity presents in a single coefficient (Nγe) for the simultaneous resistance of unit weight, surcharge, and cohesion, which is reasonable and easy to use. The results obtained from the present analysis thoroughly compared with the existing values in the literature and the significance of the present methodology for designing the shallow strip footing is discussed.

ULTIMATE SEISMIC BEARING CAPACITY OF STRIP FOOTING USING MODIFIED KREY’S METHODS (FRICTION CIRCLE METHOD)

In geotechnical investigation, determination oftheseismic bearing capacity of foundation soilconstitutes an important task. The bearing capacity of soil under static loading has been extensivelystudied since the early work of Prandtl (1921).Design of foundation in seismic areas needs specialconsiderations compared to the static case. The inadequate performance of structure during recentearthquake has motivated researches to revise existing methods and to develop new method forseismic resistant design. For foundation of structure built in seismic areas the demands to sustain loadand deformation during earthquake will probably be the severe in their design life. Due to seismicloading foundation may experience decreases in bearing capacity and increases in settlement. Twosource of loading must be taken into consideration inertial loading caused by lateral forces imposed onthe superstructure, kinematic loading caused by the ground movement developed during earthquake.Many techniques used for studying the effect of seismic forces on the soil bearing capacity such as, limitequilibrium method, kinematic approach of yield theory, a variational approach, and unified theory ofstress, which the shape of failure surface has been assumed. The seismic forces are considered as pseudostaticforces acting both on the footing and on the soil under the footing. However, finite element andstress characteristics methods shape of the failure is not required to be assumed.In the present paper, a theoretical analysis has been performed on the basis of Krey's method(friction circle method) with radius of friction circle equal to = 𝑟 sin (∅ − tan−1 𝑘ℎ1−𝑘𝑣)where r is theradius of the circle slip surface to determine the influence of the earthquake acceleration coefficientson the seismic bearing capacity of foundation with assisted by a computer program. The presentstudy is compared with the various theoretical solutions. The comparison of that the present studypredicted values of ultimate seismic bearing capacity of soil are less than others theories of ultimateseismic bearing capacity. In order facilitate the calculation of seismic bearing capacity, using theproposed equations. It is a function of (B, Rf, , tan ∅ , 𝑘ℎ and c)

Seismic bearing capacity of foundations on reinforced soil slopes

Different methods have been proposed for the analysis of the stability of reinforced soil. One of them is the method of characteristics, which treats the reinforced soil as a homogeneous but an-isotropic material. Soil masses are weak under the application of reversible/dynamic forces and reinforcing would be much helpful in these cases. In this paper, the idea of homogenization and the method of characteristics have been used to analyze the seismic bearing capacity of reinforced soil slopes. A new method has been used for deriving the equilibrium-yield equations along the characteristics, which is different from the conventional procedure used in the method of characteristics. A computer code has been written for the analysis, which calculates the geometry of plastic zone and the ultimate applicable load for the assumed material and geometrical characteristics of reinforced soil slopes. Non-uniform reinforcement and non-uniform distribution of horizontal or vertical seismic coefficients can also be considered in the analysis. Results of analysis of simple cases have been presented in the form of non-dimensional graphs to facilitate preliminary design.

Seismic bearing capacity of foundations on slopes

Seismic bearing capacity of foundations on slopes

Seismic bearing capacity of foundations on slopes

The effect of pseudo-static horizontal earthquake body forces on the bearing capacity of foundations on sloping ground has been assessed using the method of stress characteristics. Two failure mechanisms were considered, based on the extension of the characteristics from the ground surface towards the footing base from either one side or both sides. The magnitude of Nγ based on the both-sides failure mechanism, for smaller values of earthquake acceleration coefficient (αh), has been found to be significantly smaller than that obtained using the single-side mechanism; however, in the presence of αh the both-sides mechanism becomes kinematically inadmissible in many cases for higher values of ϕ. Only the single-side mechanism was found statically admissible for computing the bearing capacity factors Nc and Nq on sloping ground. All the bearing capacity factors reduce considerably with increase in αh for various ground inclinations.

Discussion: Seismic Bearing Capacity of Foundation on Cohesionless Soil

Discussion: Seismic Bearing Capacity of Foundation on Cohesionless Soil

Seismic bearing capacity of foundation on cohesionless soil : L. Dormieux & A. Pecker, Journal of Geotechnical Engineering — ASCE, 121(3), 1995, pp 300–303

Seismic bearing capacity of foundation on cohesionless soil : L. Dormieux & A. Pecker, Journal of Geotechnical Engineering — ASCE, 121(3), 1995, pp 300–303

Seismic Bearing Capacity of Foundation on Cohesionless Soil

The seismic bearing capacity of a strip-surface foundation resting on a Mohr-Coulomb material is evaluated. The upper-bound theorem of the yield design theory is used to obtain an estimate of the ultimate load. The loading parameters consist of a normal and tangential force applied to the foundation and of inertia forces developed within the soil volume. The classical Prandtl-like mechanism is used to show that the reduction in the bearing capacity is mainly caused by the load inclination; the consideration of inertia forces within the soil is only responsible for a decrease in the bearing capacity that is at least an order of magnitude smaller than the one caused by the load inclination. It is therefore concluded that, from a practical engineering standpoint, the soil-inertia forces can be neglected.