Numerical modeling and parametric study of piled rafts foundations

Abstract

This study presents a series of 3D nonlinear analysis of un-piled and piled rafts by varying raft thickness and number, spacing and diameter of piles in the group. The simulated piled rafts are square in plan and they are loaded vertically with uniform load. The soil profile utilized for analysis is a case study consisting of five layers of various properties with groundwater encountered at 3.5m from ground surface. The soil is treated as elasto-plastic material and idealized using Mohr-Coulomb model in drained condition, whereas the piles are modeled as embedded volume elements. The results show that with the increase in thickness of raft (traft), the utmost bending moment in un-piled rafts increases, whereas it decreases in piled rafts. Additionally, it has been found that, as the pile spacing decreases or piles diameter increases, the load absorbed by the piles increases as compared to that carried by the raft (pile cap) and as a result the settlement and the bending moment decreases. Further, with all traft analyzed, in 9-pile rafts of 0.5m or 0.6m diameters (dpile), the central piles absorb the largest amount of the applied load and edge piles and corner piles are placed in the next ranks, respectively. While, for all traft and each dpile utilized in the case with 25-pile rafts, a reverse behavior is observed during which the corner piles receive the upper load followed by edge piles then central piles. Moreover, piled raft foundations tend to attenuate differential settlement in structures as it makes displacements uniform.