Stability Analysis of Pile Group Subjected to Lateral Loading using Pseudodynamic Method

Pile foundations, classified under Deep foundations are used when shallow foundations are deemed unsuitable owing to soil or site conditions. Pile foundation system find wide applications in case of expansive soils such as black cotton soil and collapsible soils such as loess or when there is a layer of weak soil near the surface that cannot support the load of the superstructure. Pile foundations are subjected to significant amount of lateral loads besides vertical loads due to seismic forces. Most of the seismic analyses are complicated and require numerical analysis. Furthermore they are aimed at determining stability by considering limiting value of lateral displacement. Very limited seismic studies are conducted considering the pile group as a block. Even in the seismic studies conducted, pseudo-static approach or numerical methods are employed. The objective of this study is to analyze the response of pile group as a block in cohesion less soils subjected to seismic horizontal and vertical forces using pseudo–dynamic approach and compare the results with the existing pseudo-static method. The results of the study help us to determine the relative stability of the pile block against overturning for the avoidance of failure of the foundation system. It is observed that although the stability factor decreases with increase in the value of kv for a given value of kh. For the horizontal acceleration coefficient (kh), the effect is not as pronounced as in the case of horizontal acceleration coefficient. The variation of stability factor is negligible. Relative stability increases with the increase in the value of �•. For higher values of �• there is an increase in shearing resistance of soil. Increase in density has a negative effect on the stability of the pile block. However as the graph suggest that for all other parameters remaining same, the stability factor is higher in case of pseudo-dynamic method as compared to the pseudo-static for any given value of density. The effect of arching is reflected in pseudo-dynamic analysis where the stability factor becomes constant after a depth of about 10m.