Date of Award:

5-2016

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Committee Chair(s)

John D. Rice

Committee

John D. Rice

Committee

James A. Bay

Committee

Marc Maguire

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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