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|Title:||Assessment of the effectiveness of clay soil covers as engineered barriers in waste disposal facilities with emphasis on modeling cracking behavior|
|Authors:||Environmental Laboratory (U.S.)|
U.S. Nuclear Regulatory Commission.
Berney, Ernest S.
Hodo, Wayne D.
Peters, John F.
Myers, Tommy E.
Olsen, R. S. (Richard S.)
Sharp, Michael K.
Finite element numerical modeling
Finite element method
Radioactive waste disposal
|Publisher:||Geotechnical and Structures Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
|Series/Report no.:||ERDC TR ; 08-7.|
Abstract: This research investigated the nature of cracking behavior in compacted clay liners used for nuclear waste disposal facilities. A literature review found that, in all documented in-place clay liner studies, cracking occurred in the clay liner within 10 years, leading to failure of the liner system. Further, all moisture-flow models studied failed to capture clay cracking and the resultant high permeability associated with these failed liner systems. A laboratory investigation was undertaken to define the mechanics of the clay cracking process for a numerical model. Visual and numerical observations of cracking during drying of a highly expansive clay showed that crack formations are very diverse along the surface layer and as they migrate downward. Shapes of cracks are neither uniform nor symmetric, evolving from thin webs of microcracks to a select number of wide primary cracks that, in turn, can seal off existing microcracks. A finite element model of the soil shrinkage process was then developed, which included crack formation. Stresses within intact soil are caused by self weight (gravity stresses) and changes in water content, which induce shrinkage as a result of suction-induced tensile stresses. Two numerical simulations were run on a digital test bed similar to the laboratory study. The simulations agreed well with laboratory experimental observations, capturing all the relevant crack phenomena. The report concludes that a change in the current design criteria for clay liner systems is necessary to enable the clay to remain in a fixed, as-compacted state.
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