PULLOUT RESPONSE OF GRANULAR PILE ANCHORS IN CLAYEY SOILS

Abstract

Concurrent with the development of communication networks in recent years, many mobile communication towers have embarked at various places. These transmission towers are subjected to significant wind loads. It generates uplift forces on the foundations on one side and compression on the other side. Similarly, foundations in expansive soil are also subjected to uplift forces due to the swelling behavior of the soil. Different foundation systems in practice are capable of combating pullout forces such as bored piles, augured piles, cast in situ bored concrete piles, under-reamed piles, driven H-piles, and granular pile anchors. The granular pile anchor (GPA) system is an effective and economical foundation system to resist the pullout forces. In the GPA system, the foundation is axially anchored at the bottom of the granular pile to an anchor plate through an anchor rod. A mild steel plate of the same diameter as the granular pile is devised as an anchor plate. This anchoring arrangement through the anchor plate and anchor rod enables the GPA to offer resistance to pullout forces. The lateral swelling pressure in the surrounding cohesive soil confines the GPA radially and develops resistance against pullout. Available research work on GPA system demonstrates its applicability in resisting pullout load. Some researchers have conducted small-scale laboratory tests to study the pullout behavior of granular pile anchor foundation (GPAF) system in cohesive and non-cohesive soils. The GPA material used was a mixture of locally available sand and metal chips. Very few studies were extended to large-scale field tests. Some researcher carried out the numerical investigations of GPA system using finite element software PLAXIS 2D/ 3D to study the influence of various key parameters such as length, diameter of granular pile, and soil modulus. Limited experimental studies have been carried out to analyze the pullout behavior of GPAs in clayey soils, under inclined loading. In the present study, a series of pullout tests were conducted on a single GPA and groups of GPAs embedded in a clayey soil bed in the laboratory. The pullout response was monitored in the form of force-displacement behaviour. The pullout force was always purely vertical for a single GPA. It was vertical and inclined on the group of GPAs. The numerical modeling of GPAs was carried out using PLAXIS 2D/3D software to compare the experimental results. Hence, the present study was carried out in two phases as (i) Experimental Investigation and (ii) Numerical Investigation.