Effect of Water Drawdown and Dynamic Loads on Piled Raft: Two-Dimensional Finite Element Approach

Naveen Kumar Meena,Sanjay Nimbalkar

doi:10.3390/infrastructures4040075

Abstract

The piled raft foundations are widely used in infrastructure built on soft soil to reduce the settlement and enhance the bearing capacity. However, these foundations pose a potential risk of failure, if dynamic traffic loading and ground conditions are not adequately accounted in the construction phase. The ground conditions are complex because of frequent groundwater fluctuations. The drawdown of the water table profoundly influences the settlement and load sharing capacity of piled raft foundation. Further, the dynamic loading can also pose a potential risk to these foundations. In this paper, the two-dimensional finite element method (FEM) is employed to analyze the impact of water drawdown and dynamic loading on the stability of piled raft. The seismic response of piled raft is also discussed. The stresses and deformations occurring in and around the raft structure are evaluated. The results demonstrate that water drawdown has a significant effect on the stability and seismic response of piled raft. Various foundation improvement methods are assessed, such as the use of geotextile and increasing thickness of the pile cap, which aids of limiting the settlement.

Highlights

In Australia, many infrastructure projects are located on the soft soil
This paper reports the outcomes of finite element analysis of the piled raft foundation under two-dimensional plane strain state
The stability of the piled raft foundation subjected to seismic loads and groundwater table drawdown is evaluated

Summary

Introduction

In Australia, many infrastructure projects are located on the soft soil. Owing to high compressibility of such soils, structures are affected due to excessive differential settlement. The level of groundwater table (GWT) and loading condition influence piled raft characteristics. Moormann [11] reported that the GWT lowering influences the settlement as well as the load sharing capacity of piled raft. They considered only static loading condition, whereas dynamic loading consideration is essential. The fluctuation in GWT results in differential settlement in surrounding soil, leading to potential damage [14,15]. IItt tthhuuss bbeeccoommeess eesssseennttiiaall ttoo aasssseessss tthhee ssttaabbiilliittyy ooff ppiilleedd rraafftt aaggaaiinnsstt ddyynnaammiicc llooaaddiinngg [[2200,,2211]] ccoonnssiiddeerriinngg GGWWTT,, aanndd uunnddeerrttaakkee ttoo nneecceessssaarryy mmooddiifificcaattiioonnss ssoo tthhaatt iitt ccaann wwiitthhssttaannddaaggaaiinnsstthhiigghheerrssttrreesssseessffrroommnnaattuurraallddisisaasstteerrssaannddppoossssibiblylyeelilmimininaatetesstrtruucctuturraallddaammaaggee. This study is focused on the critical assessment of the effect of GWT drawdown and dynamic loading on piled raft foundation. The commercial software package, PLAXIS 2D v. 2012 developed by Bentley Systems is used to perform finite element analysis

Finite Element Modeling and Model Setup

Results and Discussion

Seismic Response Analysis

Conclusions