Finite element limit analysis of the seismic bearing capacity of strip footing adjacent to excavation in c-φ soil (original) (raw)
Related papers
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.
International Journal of Geotechnical Earthquake Engineering, 2015
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 methodolog...
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.
Bearing Capacity of Embedded Strip Footing Placed Adjacent to Sandy Soil Slopes
Lecture Notes in Civil Engineering, 2020
In some infrastructure projects, the strip footing adjacent to the slope is usually constructed at some depth below the ground surface. For practical engineers, estimating the bearing capacity of such footing is one of the challenging tasks. In this paper, the Finite Element Limit Analysis (FELA) is employed to determine rigorous lower and upper bounds for bearing capacity of embedded strip footing resting adjacent to a sand soil slope. The results obtained using FELA are compared with analytical approaches available in the literature. The parametric studies have been performed to examine the effect of slope angle, friction angle of the soil, footing location, and embedded depth of the footing on the bearing capacity. The results indicate that, when the strip footing is built adjacent to the sandy soil slope, the bearing capacity is reduced depending on the location of the footing relative to the crest of the slope. Also, the bearing capacity of the slope increases with the increase in the embedded depth of footing and the soil strength. Whereas, it decreases with an increase in the slope angle. The numerical outcomes are presented in design charts which can be used by the practicing engineers.
Bearing capacity of a strip footing placed next to an existing footing on frictional soil
Soils and Foundations, 2020
The ultimate bearing capacity of a single/isolated footing has been investigated intensively by many researchers. Although a lot of studies considered different aspects affecting the bearing capacity, only very few focused on the influence of an existing footing on the bearing capacity of a new footing in its close proximity. In this study, the influence of an existing footing on the ultimate bearing capacity of a recently constructed footing in a close spacing has been investigated with respect to different sizes of the footings, spacings between the footings, friction angles of the subsoil and loads applied on the existing footing. Numerical simulations based on finite-element limit analysis (FELA) are utilized to determine lower and upper bounds of the ultimate bearing capacity which bracket the exact solution from below and above. The results for isolated footings are compared with selected data from literature in terms of the bearing capacity factor N c indicating good agreement of both, lower and upper bound values. Accuracy of the results was enhanced by applying an adaptive mesh refinement technique which enabled a more precise approximation of the failure mechanism and a better estimation of the exact solution due to smaller differences between the lower and upper bound solutions. The results for footings placed next to an existing footing are discussed with regard to the interference factor n c as well as the shape and size (extend) of the failure mechanism. The results illustrate that two types of failure mechanisms may develop which either extend up to the front edge of the existing footing or pass underneath. Comparisons with previous studies revealed that interference factors have been improved significantly due to utilization of adaptive mesh refinement technique. Moreover, design charts for an estimation of n c are presented for variable footing width ratios, spacings between the footings, friction angles of the subsoil and loading factors of the existing footing.
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.