Strength and stability analyses of straight shafted pile foundation in cohesion less soil conditions using finite element method

Abstract

Foundation is an arbitrator structure to transfer the load from superstructure to the soil effectively, without any failure for both the structure and the soil. Pile foundations are meant to transfer the enormous load to the deeper depth. Straight shafted file are widely used in cohesion less soil conditions than in expensive soils. Now days these piles are designed not only to transfer the load, as a group they act as settlement reducers. These piles may be cast in situ or precast, and are required as the primary foundation support for a wide range of buildings, towers, dams and other massive structures. Analysis of pile-soil interaction is more complicated, practical testing to analyse the strength and settlement of each pile is cumbersome. The pile capacity is often difficult to assess even by means of a static loading test. The oldest approach is simply to state that the ultimate load in a test is equal to the applied load when the movement of the pile head is 10 percent of the pile toe diameter, so a proper and reliable analytical method was in urgent need to be developed. In this study analysis of straight shafted pile for has been carried out under cohesion less soil conditions (sand) by varying the length and diameter, to determine the ultimate strength and maximum displacement. For the suitability of natural condition non linear analysis need to performed implementing all the non linear characteristics of soil and linear characteristics of pile. So one of the Finite Element software’s ANSYS have been used foe the analysis. Two dimensional axisymmetric model, with pile as linear and pile soil interaction as nonlinear behaviour was considered for the modelling. Nonlinear elastic-perfectly plasticity behaviour of pile-soil interaction was assigned using Drucker-Prager constitutive model, where in interaction was modelled using Targe 169 and Conta 172 elements to produce best interaction and accurate results. Here nonlinear analysis with Incremental – iterative mixed method was carried out to obtain accurate results for axial compression loads, applied on each node. It has been identified that the pile capacity and settlement increases with increase in length and diameter of pile. But the diameter of the pile has more significance in load carrying capacity, pile capacity increases more with the increases in diameter than increases in length of the pile. The work has been concluded admitting 4m length and 0.4m diameter pile combination showed a most optimum result as compared to other combinations in case of cohesion less soil conditions.