Electronic Theses and Dissertations

Identifier

6185

Date

2018

Document Type

Thesis

Degree Name

Master of Science

Major

Civil Engineering

Committee Chair

David Arellano

Committee Member

Roger W Meier

Committee Member

Daniel Larsen

Abstract

Loess is a windblown deposit comprised primarily of silt particles that has a metastable structure characterized by randomly open and loose particle packing with high porosity. It has an ability to stand in a near-vertical slope in its unsaturated state but collpases with an increase in the degree of saturation apparently due to the loss of the effective cohesion and matric suction. The higher degree of saturation decreases the shear strength of the soil, which makes structures on loess vulnerable to collapse or excessive settlement and instability. The overall objective of this research was to find the effect of degree of saturation and dry unit weight on the shear strength of loess. To accomplish the overall objective of this research, disturbed soil samples were collected from the field and direct shear tests were performed in the laboratory for specimens with various saturation levels. The drained shear strength parameters, cohesion (c') and internal friction angle (φ'), were determined. Soil water characteristic curves (SWCCs) were prepared to determine the matric suction at different degrees of saturation. For determining the unsaturated shear strength, the friction angle indicating the increase in shear strength due to change in matric suction (φb) was estimated using three models, which was evaluated using three models, which were evaluated for loess. Using both test results, the shear strength of unsaturated loess was determined. It was found that the shear strength of loess decreases with an increase in saturation levels mainly due to a decrease in apparent cohesion resulting from the reduction in matric suction.

Comments

Data is provided by the student.

Library Comment

Dissertation or thesis originally submitted to the local University of Memphis Electronic Theses & dissertation (ETD) Repository.

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