Date of Award

1-1-2013

Document Type

Open Access Dissertation

Department

Civil and Environmental Engineering

Sub-Department

Civil Engineering

First Advisor

M Hanif Chaudhry

Abstract

Piping in an earthen levee, one of the main causes of failure, is a complex phenomenon. Most of the available research on piping failure has been on non-cohesive sandy soils. Jet Erosion Test and Hole Erosion Test have been conducted to study piping failure in an indirect manner. However, no general purpose formula is presently available to describe the erosion process due to complex erosion characteristics of cohesive soils in earthen levees.

Experimental investigations in a flume to understand the piping erosion process in an earthen levee are conducted in this research. One of the sidewalls and the bottom of the flume is built with transparent plexiglass. A side weir is used to maintain a nearly-constant upstream water level. Tests are done with a mixture of sand, silt and clay with different compaction rates. Image processing technique is applied to track the erosion process, both from the side and the bottom. The erosion process is initiated on the upstream side of the levee by removing an embedded plug. The effect of the compaction on the change in the depth, the area and the volume of erosion during the piping phenomenon are studied. Empirical equations to estimate the depth of erosion, side area of the piping zone and volume of eroded material are presented for the same soil mixture but with different compaction rate. The volume of erosion is calculated using image processing data from side and bottom views and from side views only. The former gives a more accurate estimate.

Using different mixtures of sand, silt and clay show that a minor change in the clay percentage in the soil mixtures significantly affects the time required for erosion. The ratio of the average depth of erosion to the average bottom width of piping remains approximately 1 during the erosion process. Empirical relation to estimate the depth of erosion as a function of time and the coefficient of soil erodibility for different soil mixtures with the same compaction is presented.

A one-dimensional numerical model to predict the evolution of the internal erosion in an earthen embankment is developed. The numerical model can predict the depth of erosion along the piping zone. The numerical model solves the Exner equation to predict the development of erosion depth with time. The model is used to analyze the upstream and downstream slope, the crest width, the initial upstream water depth and the initial piping diameter on the internal erosion process.

Rights

© 2013, Yusuf Ahmed Sharif

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