EXPERIMENTAL STUDY ON BEARING RESISTANCE OF SHORT DISPLACEMENT PILE GROUPS IN DENSE SANDS

Arnoldas Norkus,Vaidas Martinkus

doi:10.3846/jcem.2019.10403

Abstract

The prediction of the behavior of structures interacting with soil is one of the main challenges in structural design. Accurate evaluation of soil–structure interaction ensures a rational design solution for the superstructure and foundation of a building. In structural analysis, one of the key problems is the identification of relevant movements of the foundation considering the interaction between the superstructure, foundation and ground (the soil mass around the foundation). The correct assessment of soil–structure interaction contributes to the rational constructional design of the superstructure and foundation and allows avoiding violations of requirements for ultimate and serviceability limit states possible due to unpredicted additional stress on the structural system. Resistance predictions for pile group foundations is a complex problem, which may be the reason for scattered and insufficient information available despite numerous experimental and numerical studies, predominated by the focus on partial empirical relationships. This experimental study analyzed the prototype of a short displacement pile group with a flexible pile cap in terms of the bearing capacity and deformation behavior while subjected to static axial vertical load. In particular, attention was given to the resistance–stiffness evolution of single piles acting in a pile group with different spacing. Test results of short displacement pile groups were used to verify known models for the bearing resistance prediction of the pile group.

Highlights

A displacement pile (DP) is considered one of the most efficient foundation types because pile installation compacts granular soil increasing the load bearing resistance and stiffness of the ground
The displacement pile group (DPG) efficiency factor η for loading up to s < 0.1D is in good agreement with the predictions by Vesic (1967, 1968) and Tejchman (1973) but is in conflict with the results determined by Broms (1981), Kishida (1964), Choi et al (2017), Sales et al (2017), Gowthaman and Nasvi (2018), Sharma et al (2019), yielding η < 1
Tests determined an increase of η when decreasing the spacing a in dense sands, and this result conflicts with the results reported by Gogoi et al (2014) and Gowthaman and Nasvi (2018)

Summary

Introduction

A displacement pile (DP) is considered one of the most efficient foundation types because pile installation compacts granular soil increasing the load bearing resistance and stiffness of the ground (the soil mass around the pile). Analytical and empirical models for the prediction of the ground resistance were developed for long piles (the slenderness ratio L/D ≥ 20); the suitability of the proposed prediction methods for less slender (short) piles (which are frequently used in Lithuania (L/D ≈ 5–6)) should be verified experimentally. The study aimed to conduct the static axial compression tests and perform a resistance analysis for a short single displacement pile (SDP) and a short displacement pile group (DPG), both installed in an artificially created sand deposit

Ground resistance of a pile and pile group

Single pile tests

Findings

Tests for the pile groups with the 3D spacing

Concluding remarks