Date of Award

August 2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Engineering

First Advisor

Sam Helwany

Committee Members

Al Ghorbanpoor, Hani Titi, Istvan Lauko, Nathan Salowitz

Keywords

Bearing capacity, Cyclic thermal load, Energy pile, Fatigue, Shear strength

Abstract

In the present work, the side resistance of an energy pile subjected to a significant number of thermal cycles in saturated Kaolin clay was investigated through small-scale pile tests, direct shear tests, and triaxial tests. Before applying compressive load, relative shearing displacement, or deviator stress, up to 36 cooling/heating cycles were performed on the soil-foundation interface and soil. The thermal cycle was below the average ground temperature in temperate zones to simulate the winter-mode operation. In small-scale pile tests, the long-term behavior of the pile was observed in terms of temperature distribution and pore water pressure in soil, and a 15% relative settlement criterion was adopted to define the failure load. In direct shear tests, failure is taken to correspond to the maximum shear stress attained, or shear stress at 10% relative shear displacement. In triaxial tests, failure is taken to correspond to the maximum deviator stress attained, or deviator stress at 15% axial strain. If soil is subjected to long-term temperature cycling, however, time plays an essential role in affecting mechanical performances. Therefore, under ambient temperature, a series of tests were carried out in direct shear tests and triaxial tests to analyze the effect of time of which is referred to as an aging influence. The results show that the pile subjected to temperature cycling has weaker side resistance than the isothermal pile tested at room temperature due to soil erosion by condensate water, but this is not the case for the soil-foundation interface in the direct shear test. In direct shear tests and triaxial tests, although the heating/cooling cycles induced the clay to have a significant contraction, the elapsed time of temperature cycling is the main factor for increasing the resistance to shear deformation.

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