Degree Type

Thesis

Date of Award

2011

Degree Name

Master of Science

Department

Civil, Construction, and Environmental Engineering

First Advisor

Sri Sritharan

Abstract

In the past decades, the behavior of pile foundations in liquefiable sands has been studied extensively; however, similar investigations of soft clays or static/seismic response of piles in improved soft clay soils are scarce. Despite the widespread presence of this soil type in high seismic regions and the frequent need to locate bridges and buildings in soft clay, only a few investigations have been carried out to guide engineers in evaluating the effectiveness of ground improvement techniques on increasing the lateral resistance of pile foundation embedded in soft clay, and no numerical models have been validated to evaluate this approach. Thus, the objective of this research was to develop modified p-y curves for Winkler analysis to characterize the lateral load behavior of a single pile embedded in a volume of improved clay surrounded by unimproved soft clays.

A detailed literature review was completed in the study, aiming to gain knowledge on the development and fields of applications together with limitations of different ground improvement techniques. The ability of each available analysis method for lateral loaded piles was assessed for determining lateral responses of pile foundation in a volume of improved soil surrounded by unimproved soil.

A method of developing p-y curve modification factors to account for the effect of the improved soil on enhancing the lateral load behavior of a single pile embedded in soft clay was developed by integrating the effectiveness of the improved soil into the procedures of constructing p-y curves for stiff clay recommended by Welch and Reese (1972). It was achieved by estimating the effective length for a infinitely long soil layer with soil improvement so that the fraction of the load resisted by the soil improved over a limited horizontal extent could be accounted for by taking the ratio between the soil resistance attenuation at actual length of the soil improvement and the effective length. The accuracy of the method was verified against the centrifuge test data from Liu et al. (2010) and the full scale field test from Fleming et al. (2010). The verifications using experimental data demonstrated that the Winkler analysis with proposed p-y modification factors is able to capture the full range of elastic and inelastic pile responses with slopes that correspond well with the results obtained from both centrifuge and field testing, the effectiveness of the soil improvement can be adequately evaluated.

In addition, an analytical study on the effectiveness of the cement-deep-soil-mixing (CDSM) ground improvement technique on controlling the lateral displacement of pile foundations embedded in different clay soil conditions with and without ground improvement was carried out. A set of lateral load analyses was performed to establish permissible displacements for precast, prestressed concrete piles as well as open-ended steel pipe pile prior to reaching the curvature capacity of piles. The analysis results showed an average of 66% reduction on the permissible displacement limit by providing a volume of CDSM soil improvement around the prestressed precast concrete piles embedded in medium clay and soft clay. And an average of 79% reduction was observed on steel pipe pile embedded in CDSM improved medium clay and soft clay.

DOI

https://doi.org/10.31274/etd-180810-1393

Copyright Owner

Jin-wei Huang

Language

en

Date Available

2012-04-30

File Format

application/pdf

File Size

149 pages

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