Date of Award:

2016

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Advisor/Chair:

John D. Rice

Abstract

Internal erosion often occurs when seepage flow is concentrated into a small, unprotected opening. One such example is where sandy soil is eroded through a defect in an overlying clay layer, resulting in a sand boil in the process. The erosion initiates through the heave and backward piping mechanisms and continues beneath the clay layer through the piping process, forming a pipe that progresses toward the source of the seepage. The initiation of erosion at the seepage flow concentration is a complex mechanism involving a number of hydraulic and soil mechanics principles, including: flow concentration, soil arching, heave, detachment of soil grains, and transportation of soil grains.

A laboratory testing program is being performed to investigate the mechanisms of erosion into a concentrated, unprotected exit. The study builds upon previous research on the mechanisms of piping initiation performed at Utah State University and uses a similar apparatus. A number of different soils representing a range of grain size, grain shape, and gradations are being forced to erode into a range of constricted seepage exits. The exit is fixed with a riser pipe to model the upward transport of eroding soils. The results are compared with axisymmetric finite element analyses in order to develop a better understanding of the initiation process for backward erosion piping.

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