Indian Journal of Science and Technology

Abstract

Objective/methods: Pile load test is commonly carried out at ground level assuming that using sleeve eliminates shaft resistance within the planned excavation area. But these tests do not capture the effect of stress relief due to excavation. So to study its effect on pile behavior, three numerical simulations were carried out using finite element method. The first simulation (L_Ground) was carried out at the ground level. The second simulation (L_Sleeve) was conducted using sleeve in the planned excavation area. The length of sleeve was taken equal to the depth of basement. The third simulation (L_ Excavation) was carried out after excavation at the formation level.

Findings/application: It was found that Q_LE is 85% of Q_LS so when tests are conducted by using a sleeve, pile capacity is overestimated. Q_LG is 74% of Q_LS which is less than Q_LE. Because after excavation, soil particles around the pile are stiffer so capacity is increased. At ground level, at working load shaft carries about 77% load. When the load is increased and reaches the ultimate value end bearing contributes more than the shaft resistance. On the other hand, for sleeved pile, at working load shaft and end bearing carries about 80 and 20% load, respectively. But at ultimate load, shaft carries 55% load which is still greater than that carried by end bearing. While after excavation, at working load shaft carries about 86% load. When ultimate load is reached the load distribution is similar to sleeved pile. In the case of ground level and excavation, the shaft resistance has been fully mobilized at the load less than Q_LS that is about 74 and 86% of Q_LS, respectively. These results will help to estimate the pile capacity in a better way.

Keywords: Stress Relief, Pile Capacity, Soft Clay.