Date of Award:

5-2013

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Advisor/Chair:

John D Rice

Abstract

Seepage barriers have been used extensively to mitigate seepage problems in dams and levees. Although the designs of many of these dams and levees have been based on intact seepage barriers, seepage barriers have been shown to be susceptible to deformation and cracking when high differential hydraulic pressures act across the barrier. Cracking and deformation have also been observed due to thermal expansion and contraction during seepage barrier curing. Under certain conditions, a crack can lead to serious seepage problems, which could potentially lead to the development of a low-resistance seepage pathway. Three scenarios have been identified where there is potential for erosion to occur adjacent to a crack in a barrier: 1) erosion at the interface between a fine-grained soil and a course-grained soil, 2) erosion of overlying soil due to flow along a joint in bedrock, and 3) erosion of the barrier material itself. Previous studies have investigated the first mode of erosion and studies are underway to look into the second mode. The objective of this study is to investigate the third mode of erosion and to identify the conditions under which serious seepage problems can develop. The question considered was whether the combination of highly permeable material adjacent to a crack in a seepage barrier and a large differential head across the barrier combine to develop a velocity within the crack that is erosive to the seepage barrier material. Laboratory tests have been performed on a variety of seepage barrier materials to assess the potential for cracks to develop a preferred seepage path leading to a serious seepage problem. The results of this study will be useful in risk assessment studies of dams and levees with existing seepage barriers as well as in the design of new seepage barriers. Having knowledge of the conditions under which problems may occur will aid in the selection of seepage barrier types for new barriers, placement of instrumentation to monitor new and existing barriers, and mitigation of existing barriers where problems have been identified. The data provided will assist engineers in quantitatively assessing the potential for the propagation of critical seepage problems from cracks in seepage barriers.

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