Evaluation of the Response of Piled Raft Systems in Soft Soil Undergoing Consolidation and Pore Pressure Drawdown

The paper presents the results of a numerical investigation to study the time-dependent settlement and structural behaviour of piled raft foundations due to consolidation and subsidence. It is well understood that structures constructed on soft soils undergo large deformations with time. Moreover, few researchers have concluded that due to consolidation and pore pressure drawdown (dewatering and pumping), there is a possibility of separation of the raft from the soil, which can lead the piles to take higher loads than the design loads. A 3D numerical model of a piled raft foundation using finite element approach was incorporated in this paper. The validation was done with the reported experimental results. A parametric study was conducted to study the variation in the distribution of axial load along the pile undergoing consolidation and drawdown, the increase in settlement with time, and the load transfer from the raft to the pile head due to the process of consolidation and drawdown with variation in the pile slenderness ratio. From the finite element simulations, it was observed that soil continues to settle as a result of pore pressure drawdown. Therefore, large drag force occurs in the piles. As the soil continues to settle, the contact pressure between raft and the soil reduces, thereby changing the working conditions of the piled raft. Pile takes additional load due to the loss in shearing strength of the soil at the raft-pile interface, which may result in the failure of the piles. The maximum axial force transmitted to the piles after drawdown is 1.02 to 1.77 times higher than that transmitted during structural service load. Therefore, the need to study the effect of consolidation and drawdown on the serviceability and structural aspects of piled raft is of utmost importance.