Optimization Method for Irregular Piled Raft Foundation on Layered Soil Media

Yunfei Xie,Shichun Chi

doi:10.1155/2019/5713492

Abstract

Important buildings such as nuclear power plants always require stricter control of differential settlement than ordinary buildings. Therefore, it is necessary to provide an optimized design for the piled raft foundations of important buildings. In this paper, a new optimization method (using different pile diameters and different pile spacing) was proposed for the design of piled raft foundations. This method adjusts the pile diameters and pile spacing according to the stress distribution at the pile top of the initial design to achieve a more uniform settlement of the raft and stress distribution on top of piles, which can solve the differential settlement problems caused by uneven loads of the superstructure. After optimized design, the differential settlement and integral bending moment of the raft decreased more than 64% and 52%, respectively, and the differential stress on top of piles decreased by at least 63%. The new method proposed in this paper could be applied to large-scale piled raft foundations with complex superstructure loads.

Highlights

Rigid foundations are a good choice for important buildings to resist static loads and seismic loads, but the rigid foundations are always limited
The differential settlement of the Piled raft foundations (PRFs) designed by the conventional method for ordinary buildings may not satisfy the requirements of important buildings. e piles are usually uniformly arranged in conventional PRF designs, that is, a consistent pile diameter, length, and spacing
Mathematical optimization methods can solve the problems through a combination of mathematical tools and numerical methods; accurate optimal results can be obtained, but it is difficult for ordinary engineers to learn. e main idea of the BSDPT optimization method proposed in this paper is to reduce the differential settlement through adjusting the pile diameters and spacing according to the stress distribution on top of the pile group

Summary

Introduction

Rigid foundations are a good choice for important buildings to resist static loads and seismic loads, but the rigid foundations are always limited. Piled raft foundations (PRFs) have been widely adopted in the design of high-rise buildings and important buildings in recent years due to their efficiency in controlling the total settlement and differential settlement and their high bearing capacity [1]. The differential settlement of the PRF designed by the conventional method for ordinary buildings may not satisfy the requirements of important buildings. Truman and Hoback [12] proposed a combined finite element (FE) and optimization technique to minimize the system-wide distortion of PRFs. Using a centrifuge model test and an extensive parametric study, Randolph [13] and Nguyen et al [14] verified that differential settlement could be effectively reduced by adding several piles in the center of a raft. The differential settlement and the differential stress on top of the pile group and the maximum integral bending moment of the raft all decrease more than 50%, which allows an optimal and economical raft-pile system to be obtained without the need for complex iterative computations

Optimization Method

Result

Model Validation

Optimized Design under Various Pile Diameters