Semester of Graduation

summer 2020

Degree

Master of Civil Engineering (MCE)

Department

The Department of Civil and Environmental Engineering

Document Type

Thesis

Abstract

This study aimed at investigating the effect of heating-cooling cycles on the interface strength parameters of clay soil-concrete for potential applications to improve the side capacity of piles driven in clayey soil by the heating process, and also to assess the behavior of geothermal piles regarding interface shear strength parameters. A modified large-size direct shear test device with the dimensions 12” x 12” x 8”, was used in this study. A concrete block (12” x 12” x 4”) of similar texture and smoothness to the concrete piles was used to simulate the pile interface. The tested clays are low plasticity index, P.I., clay (PI=12), medium plasticity index, P.I., clay (PI=30), and high plasticity index, P.I., clay (PI=60). All three types of clay soils were tested under one heating-cooling cycle of (20o - 70o - 20o) C temperatures. Only the low P.I. clay soil was also tested under two different heating-cooling cycles of (20o - 55o - 20o) C temperatures and (20o - 40o - 20o) C temperatures. In addition, it was tested under 16psi and four number of heating-cooling cycles of (20o - 70o - 20o) C, (20o - 55o - 20o) C, and (20o - 40o - 20o) C temperatures. Furthermore, the low P.I. clay soil was also tested under nine number of heating-cooling cycles of (20o - 55o - 20o) C temperatures under 16psi. A heating system was designed and used to apply up to 70°C temperature on the soil-concrete inside the direct shear test device. The experimental program includes shearing the three different types of clay soils for both conditions: without applying heating-cooling, and with applying heating-cooling cycles under three different normal stresses (10psi, 16psi, and 21.8psi), and also under 4.35psi normal stress for the low P.I. clay. After consolidation, the temperature for the heated specimens was increased gradually during the heating process from room temperature (22°C ±1°C) up to the target temperature, and then, during the cooling process, the specimens were cooled back to the room temperature. The test results of this study showed a significant increase of interface peak shear strength, cohesion, and the peak friction vii angle of the heated high P.I. soil specimens, while insignificant change was observed in residual shear strength parameters. However, for low and medium P.I. clay soils, the results showed an increase in both peak and residual interface shear strength parameters. In addition, the increase in shear strength parameters of the low P.I. clay was found to be proportional with number of cycles and the target temperature.

Committee Chair

Abu-Farsakh, Murad

DOI

10.31390/gradschool_theses.5148

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