Horizontal Loading Tests on Disconnected Piled Rafts and a Simplified Method to Evaluate the Horizontal Bearing Capacity

Xiao-Jun Zhu,Kang Fei,Sheng-Wei Wang

doi:10.1155/2018/3956509

Abstract

Disconnected piled raft (DPR) foundations have been widely adopted as an effective foundation system where the piles are separated from the raft by a granular layer, which can limit the shear forces and moments transmitted between the raft and the piles. Thus, DPR foundations may avoid the problem of horizontal forces, such as those from an earthquake or dynamic loads, which damage the structural connection between the pile head and raft. A series of static horizontal loading tests were carried out on three types of foundation models, i.e., piled raft, disconnected piled raft, and raft alone models, on fine sand using a geotechnical model in a 1 g field. In this paper, the influences of vertical loading and interposed layer thickness were presented and discussed. The results showed that most of the horizontal force was carried by raft/interposed layer friction in the DPR foundation type, and the shear force and moment of the piles were greatly reduced due to the gap between the raft and the heads of the piles. The tested foundations were simulated using a simplified method with theoretical equations derived by making several approximations and assumptions. The simulated results agreed well with the test results.

Highlights

In situations where a raft foundation alone does not satisfy the design requirements, it may be possible to enhance the performance of a raft by adding piles, producing what is called a piled raft [1,2,3]
The Rion–Antirion Bridge in Greece [6, 7] and the ICEDA nuclear waste storage facility [8] were founded on clay reinforcement by settlement-reducing piles with an interposed granular load distribution layer, which can limit the shear forces and moments transmitted between the raft and the subsoil
According to the horizontal force transfer mechanism of DPR foundations, if the pressure distributed on the bottom of the raft is uniform and experiences vertical and horizontal load, its horizontal bearing capacity is composed of the bearing capacity of the raft structure, the

Summary

Introduction

In situations where a raft foundation alone does not satisfy the design requirements, it may be possible to enhance the performance of a raft by adding piles, producing what is called a piled raft [1,2,3]. Erefore, the concept of a disconnected piled raft has been discussed, where the piles are separated from the raft with an interposed granular load distribution layer [4, 5]. The Rion–Antirion Bridge in Greece [6, 7] and the ICEDA nuclear waste storage facility [8] were founded on clay reinforcement by settlement-reducing piles with an interposed granular load distribution layer, which can limit the shear forces and moments transmitted between the raft and the subsoil. The behaviour of the DPR under a seismic load has not been well clarified, which is partly due to the uncertainty in the complicated behaviour of the disconnected piled raft when it is subjected to seismic and lateral loads

Methods

Results

Conclusion