ORCID Identifier(s)

0000-0002-0617-2458

Graduation Semester and Year

2022

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Sahadat Md Hossain

Abstract

Each year significant number of highway slope failures are reported in the United States, especially in states like Texas where expansive clayey soil is prevalent. Slopes constructed over expansive clay often experience recurring shallow failures following their construction which poses maintenance problems to the Texas Department of Transportation (TxDOT). These shallow slope failures can be primarily attributed to the considerable volume change that expansive clay soil undergoes from seasonal climatic variation. Furthermore, under unsaturated conditions during dry periods, high matric suction (i.e., negative porewater pressure) exists in soil slopes. The existence of matric suction contributes to the shear strength of the soil. Contrastingly, during prolonged wet periods, sufficient infiltration occurs into the slope and decreases the matric suction of the soil. The loss of matric suction in turn results in an increase in soil water content and subsequent reduction of the additional shear strength provided by the matric suction eventually leading to shallow slope failures. Since rainfall infiltration is a major cause of shallow failures of highway slopes, it is worthwhile to study preventive measures that can minimize rainfall infiltration into soil slopes which will in turn maintain the long-term stability of the slope. Conventional slope stabilization methods include earthwork, moisture control and mechanical reinforcement methods. To this end, a slope stabilization method was developed utilizing the modified moisture barrier to minimize rainfall intrusion into a soil slope. A portion of a failed section of a highway slope located along interstate highway 20 in Arlington, Texas was designed to be stabilized with a modified moisture barrier. The failed section was divided into two test sections modified moisture barrier and recycled plastic pins sections, while a portion of the original slope was established as the control section. The test sections were instrumented with integrated temperature-moisture sensors, soil water potential sensors, and vertical inclinometer casings. Additionally, a topographic survey of the slope was conducted using a total station and field hydraulic conductivity testing was carried out in the test sections. Measurement of volumetric water content and matric suction revealed that the control section experienced instantaneous fluctuations with respect to rainfall events while that of the MMB section was considered insignificant. The maximum variation of moisture content in the control section ranged from approximately 14.7 to 32.6 % while that of the MMB section was almost constant. The insignificant change in moisture content of the MMB section soil was reflected in the field measurements of soil permeability. The hydraulic conductivity of the soil under the MMB section remained almost constant while that of the other sections showed considerable variation with time and rainfall, as exposed to climatic conditions. The insignificant fluctuation of the moisture content in the MMB section also influenced the lateral and vertical movement of the slope. The MMB section experienced maximum lateral deformation of 0.29 inches over a monitoring period of 36 months which was about 40% lower than that of the control section while the RPP section showed maximum lateral movement of 0.26 inches. In comparison, the MMB and RPP section showed a very similar reduction in maximum lateral deformation of the slope compared to the control section. Similar trend was observed in the vertical settlement of the slope: the MMB section showed 65% reduction in movement compared to the control while that of the RPP section was 37% less. Therefore, it can be concluded that use of the modified moisture barrier reduces the lateral and vertical settlement of the slope caused by the swell-shrink behavior of expansive soil by controlling rainfall infiltration.

Keywords

Expansive soil, Volume change behavior, Rainfall induced shallow slope failure, Modified moisture barrier, Field hydraulic conductivity, Prediction model

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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