Pseudo-Dynamic Bearing Capacity of Shallow Strip Footing Resting on c-Φ Soil Considering Composite Failure Surface (original) (raw)
Related papers
Pseudo-dynamic analysis for bearing capacity of foundation resting on c –Φ soil
International Journal of Geotechnical Engineering, 2014
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-W 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 (N ce) 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.
Seismic bearing capacity of shallow strip footings
The seismic bearing capacity factors for shallow strip footings embedded in sloping ground with general c-soil are found out by using the limit equilibrium method. The seismic forces are considered as pseudostatic forces acting both on the footing and on the soil below the footing. A composite failure surface involving planar and logspiral is considered in the analysis. A new methodology to establish minimum bearing capacity factors has been adopted by numerical iteration technique to determine the critical focus of the logspiral. Three different types of failure surfaces are considered depending on the embedment depth and ground inclinations. The seismic bearing capacity factors with respect to cohesion, surcharge and unit weight components viz. N cd , N qd , and N ␥d , respectively, are found out separately for various values of soil friction angles and seismic acceleration coefficients both in the horizontal and vertical directions, ground inclinations, and embedment depths. Results of the present study are reported in tabular form. The effect of parametric variation on seismic bearing capacity factors has been studied. Comparisons of the proposed method with available theories in the seismic case are also presented.
Seismic Bearing Capacity of Strip Footing
At present there are quite a number of available methods, to predict the bearing capacity of a strip footing under dynamic loads, but it is not evident which one of these methods predicts more accurately under a given situation. From the viewpoint of possible earthquake effects, India is divided into four zones, for computing seismic forces, either seismic coefficient method (used for pseudo static design of foundations of buildings & bridges) or response spectrum method (used for the case of earth dam) is used [5]. These forces along with the static forces make the foundation subjected to eccentric inclined load. If the resultant load on the foundation has an eccentricity 'e' only in one direction then the dimension of the foundation in that direction is allowed to be reduced by '2e'. In this condition it is proposed to study changes of allowable bearing capacity during earthquake for strip footing on sandy soil for various ranges of width of foundation (B), angle of shearing resistance (Φ) of supporting soil and intensity of earthquake from different available theories to check the relativities of such theories. The majority of available solutions in the literature are analytical. Solutions for dynamic bearing capacity for identical foundation were obtained and comparison were made to seek relative differences between the results from such different theories for varying seismic condition.
Static and seismic bearing capacity of shallow strip footings
Soil Dynamics and Earthquake Engineering, 2016
In this study, the evaluation of static and seismic bearing capacity factors for a shallow strip footing was carried out by using the method of characteristics, which was extended to the seismic condition by means of the pseudo-static approach. The results, for both smooth and rough foundations, were checked against those obtained through finite element analyses. Under seismic conditions the three bearing capacity problems for N c , N q and N γ were solved independently and the seismic bearing capacity factors were evaluated accounting separately for the effect of horizontal and vertical inertia forces arising in the soil, in the lateral surcharge and in the superstructure. Empirical formulae approximating the extensive numerical results are proposed to compute the static values of N γ and the corrective coefficients that can be introduced in the well-known Terzaghi's formula of the bearing capacity to extend its applicability to seismic design of foundations.
Geomechanics and Geoengineering, 2020
In this study, several effective parameters and geometrical features were considered to present the design charts and the reduction coefficients tables to obtain the bearing capacity of a strip footing placed near a c-ϕ excavation under static and seismic conditions by using Finite Element Limit Analysis (FELA). The effects of setback distance to footing width ratio (L/B), cohesion (c), soil friction angle (ϕ), pseudo-static horizontal earthquake coefficient (k h), and the height of the excavation to the footing width ratio (H/B) on the bearing capacity and failure mechanism were studied. Also, a design procedure and example of its application were presented to obtain the static and seismic bearing capacities of the strip footing placed near the c-ϕ excavation based on the design charts and the reduction coefficients tables.
JES. Journal of Engineering Sciences, 2014
In geotechnical investigation, determination oftheseismic bearing capacity of foundation soil constitutes an important task. The bearing capacity of soil under static loading has been extensively studied since the early work of Prandtl (1921).Design of foundation in seismic areas needs special considerations compared to the static case. The inadequate performance of structure during recent earthquake has motivated researches to revise existing methods and to develop new method for seismic resistant design. For foundation of structure built in seismic areas the demands to sustain load and deformation during earthquake will probably be the severe in their design life. Due to seismic loading foundation may experience decreases in bearing capacity and increases in settlement. Two source of loading must be taken into consideration inertial loading caused by lateral forces imposed on the 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, limit equilibrium method, kinematic approach of yield theory, a variational approach, and unified theory of stress, which the shape of failure surface has been assumed. The seismic forces are considered as pseudostatic forces acting both on the footing and on the soil under the footing. However, finite element and stress 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 = sin (∅ − tan −1 ℎ 1−)where r is the radius of the circle slip surface to determine the influence of the earthquake acceleration coefficients on the seismic bearing capacity of foundation with assisted by a computer program. The present study is compared with the various theoretical solutions. The comparison of that the present study predicted values of ultimate seismic bearing capacity of soil are less than others theories of ultimate seismic bearing capacity. In order facilitate the calculation of seismic bearing capacity, using the proposed equations. It is a function of (
Seismic bearing capacity of shallow strip footings embedded in slope
The seismic bearing capacity factors for shallow strip footings embedded in sloping ground with general c-soil are found out by using the limit equilibrium method. The seismic forces are considered as pseudostatic forces acting both on the footing and on the soil below the footing. A composite failure surface involving planar and logspiral is considered in the analysis. A new methodology to establish minimum bearing capacity factors has been adopted by numerical iteration technique to determine the critical focus of the logspiral. Three different types of failure surfaces are considered depending on the embedment depth and ground inclinations. The seismic bearing capacity factors with respect to cohesion, surcharge and unit weight components viz. N cd , N qd , and N ␥d , respectively, are found out separately for various values of soil friction angles and seismic acceleration coefficients both in the horizontal and vertical directions, ground inclinations, and embedment depths. Results of the present study are reported in tabular form. The effect of parametric variation on seismic bearing capacity factors has been studied. Comparisons of the proposed method with available theories in the seismic case are also presented.
Civil and Environmental Engineering Reports, 2021
The use of geosynthetic reinforcement to enhance the ultimate load-bearing capacity and reduce the anticipated settlement of the shallow foundation has gained sufficient attention in the geotechnical field. The improved performance of the shallow foundation is achieved by providing one or more layers of geosynthetics below the foundation. The full wraparound technique proved to be efficient for the confinement of soil mass and reduction in settlement of foundation however lacks the literature to ascertain the performances of such footing under dynamic loading. In view of the above, the present study examines the effect of geosynthetic layers having a finite length with full wraparound ends as a reinforcement layer, placed horizontally at a suitable depth below the foundation using the finite element modeling (FEM) and evaluates the ultimate load-bearing capacity of a strip footing resting on loose and dense coarse-grained earth beds under seismic loading and further compared to thos...
Iranian Journal of Science and Technology, Transactions of Civil Engineering, 2019
The subject seismic bearing capacity is one of the most important aspects of geotechnical earthquake engineering. As the existing pseudo-dynamic method has certain drawbacks, this paper presents a modified pseudo-dynamic approach to evaluate the seismic bearing capacity of shallow strip footing resting on c-Φ soil considering the log-spiral failure mechanism. Since damping is present in all materials, more realistic results can be obtained by modeling the soil as a visco-elastic material. Here, the passive failure region is considered a fully log-spiral zone with an arbitrary location of the center of log-spiral. A single seismic bearing capacity coefficient (N γe) is evaluated for the simultaneous resistance of unit weight, surcharge and cohesion, which is more practical to simulate the field failure mechanism. The effects of soil and seismic parameters are taken into account to evaluate the seismic bearing capacity of the 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 a reasonably good agreement is found with the existing studies.
Static and dynamic bearing capacity of strip footings, under variable repeated loading
The problem of bearing capacity of strip footings is one of the basic and classical problems of geotechnical engineering. Footings under variable repeated loads are vulnerable to collapse due to accumulation of plastic strains or inadaptation. Unlike common limit state methods, the shakedown method can be applied to investigate the behavior of structures subjected to loads varying and repeating in time. In the present study, shakedown theory is employed to determine the static and dynamic bearing capacity of strip footings under variable repeated loads. Effects of load variation and repetition on bearing capacity of footing are studied thoroughly for both static and dynamic loadings. The results indicate that the dynamic bearing capacity of footings is sensitive to dynamic properties of load and subsoil. In addition, results are compared to the bearing capacity of a footing obtained by the common limit state methods.