Graduation Semester and Year

2020

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

J Anand Puppala

Second Advisor

Laureano Hoyos

Third Advisor

Xinbao Yu

Fourth Advisor

Eric Jones

Abstract

The problem of slope stability in earthen dams is a major concern to geotechnical engineers. Traditionally, the seepage through embankments and other geotechnical structures is estimated using hydraulic properties of saturated soil. In most of the cases, the soil is not fully saturated and use of saturated soil properties can lead to erroneous results. The reliable assessment of slope stability needs comprehensive characterization of both unsaturated and saturated hydraulic properties of soil. The coefficient of permeability is a key hydraulic property in solving any flow related problem in geotechnical engineering. The permeability coefficient of unsaturated soil is usually estimated using existing permeability models derived from Soil Water Characteristic Curve (SWCC) of soil. The performance of these prediction models has not been consistent in the past. The proper determination of unsaturated soil permeability properties will be needed for better stability designs and checks of earth structure. Hence, the primary objective of this research is to study and determine unsaturated soil hydraulic properties and then use them in a slope stability framework of earthen dams. As a part of this research, a comprehensive experimental program is designed to evaluate the influence of matric suction, net confining stress, wetting and drying cycle on hydraulic conductivity of a clayey soil over wide range of suction values. A modified suction – controlled triaxial equipment was used to apply and maintain suction and hydraulic head in soil specimen to measure the coefficient of permeability on drying and wetting cycles. Since cyclic drying and wetting induces hysteretic effects in hydraulic properties of partially saturated soils, a study was performed to determine hysteretic permeability of control soil. As many of the dam and levee embankments can be stabilized with lime treatments, experimental studies were undertaken to understand the effect of lime treatment on the same permeability coefficients and slope stability assessments. The final outcome of this research includes a finite element model based slope framework which can model dam slopes using both steady state and transient seepage in saturated-unsaturated soil conditions. A series of fully coupled hydro – mechanical numerical analyses were performed to examine the effect of unsaturated hydraulic properties of soil on pore water pressure and safety factors of slope for transient seepage conditions during drawdown. The effect of stress – dependent hydraulic properties and hydraulic hysteresis on transient seepage was also investigated. The findings from this study would highlight the role of hydraulic properties of partially saturated soil in seepage and slope stability analyses of earthen dam.

Keywords

unsaturated soil, permeability

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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