Title

Load-settlement and stress-strain behaviour of geotextile-reinforced sandy soil

Author Identifiers

Shadi Aria

ORCID ID: 0000-0003-4963-9174

Date of Award

2018

Degree Type

Thesis

Degree Name

Doctor of Philosophy

School

School of Engineering

First Advisor

Associate Professor Sanjay Kumar Shukla

Second Advisor

Dr Alireza Mohyeddin

Abstract

During the past few decades, many studies have been conducted to investigate the load-settlement behaviour of geosynthetic-reinforced foundations, and researchers proposed different methods to improve the performance of geosynthetic-reinforced foundation soils as well as to develop empirical equations to estimate their bearing capacity. In the recent past, using geotextile reinforcement with wraparound ends has been recommended to strengthen the foundation soil aimed at improving the effectiveness of using geosynthetic reinforcements. However, there are still areas that received far too little attention in the past, e.g. the optimum geometric parameters in geosynthetic-reinforced sandy soils with or without using wraparound reinforcement technique. An optimal design and the effectiveness of employing geosynthetic material for strengthening the foundation soil require an extensive knowledge of the load-settlement behaviour and failure mechanism of reinforced soils.

This thesis presents extensive laboratory measurements and numerical analysis conducted to (i) investigate the effect of angle of internal friction of soil on the optimum burial depth of the reinforcement and the bearing capacity of the geosynthetic-reinforced sandy soil based on numerical modelling, (ii) study the effects of reinforcement geometrical parameters, namely land width occupied by the reinforcement, and the lap length of the wrapped ends, based on numerical modelling, (iii) present experimental evaluations of the effectiveness of the wraparound reinforcement technique for improving the bearing capacity and load-settlement characteristics of sandy soils, and (Das & Sivakugan) study the strain distribution and the mobilisation of tensile modulus in geotextile reinforcement buried within the sandy soil. In the experimental phase, laboratory model strip footing tests were performed to investigate the influence of wraparound lap length and occupied land width on the load-settlement behaviour of sandy soil. In addition, an instrumentation program with pressure cells and strain gauges was designed to investigate stress and strain distribution within the sand bed. The test results show that the existence of wraparound ends of the geotextile reinforcement improves the bearing capacity of sand bed by about 70% comparing with reinforced foundation soil without wraparound ends. The strain distribution observations reveal that the theoretical solution may overestimate the tensile strength of the geotextile in the range of 30-60 % that can be due to the in-isolation methods being used by standards to measure the tensile modulus of geosynthetics.

In the numerical phase, first, a numerical model was built to investigate the effect of the angle of internal friction of sand on the optimum burial depth of geosynthetic reinforcement. Numerical outputs reveal that the optimum burial depth depends significantly on the angle of internal friction of sand, and has a linear relationship with the height of the active wedge beneath the footing. In the second stage, a parametric study of the wraparound reinforcement technique was carried out to investigate the effects of geometrical parameters of wraparound reinforcement on the bearing capacity of the sandy soil. The model was used to critically analyse the reinforcing mechanisms for improved bearing capacity caused by wraparound ends. The results reveal that the efficiency of reinforced models with wraparound ends in terms of occupied land area is about 100% higher than that of without wraparound ends. The research carried out as presented in this thesis demonstrates that the wraparound geosynthetic reinforcement technique can be highly beneficial in a location of limited land width for foundation construction.

Access Note

This thesis is under embargo for two years and will be available on 18 February 2021.

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