Use of Perforated Base Pedestal to Simulate the Gravel Subbase in Evaluating the Internal Erosion of Geosynthetic Clay Liners

Abstract

Abstract When geosynthetic clay liners (GCLs) are placed over coarse-grained gravel subgrades, the permittivity of the GCLs may increase because of internal erosion. To simulate this condition, geosynthetic clay liners typically are placed over gravel and tested in the laboratory under high hydraulic heads. In this study, a perforated base pedestal was used instead of gravel. The base pedestal was designed to have circular voids to represent the voids of a uniform and rounded gravel subgrade. Results obtained from tests where natural gravel and a perforated base pedestal were used were compared. To verify the effectiveness of the new approach, two different geosynthetic clay liners were tested over two different gravel subgrades. Tests also were conducted using rounded, uniform, coarse-grained gravels to compare to the results of the tests with the perforated base pedestals. The void diameter of the perforated base pedestals was chosen to be approximately the same as the maximum void size between the gravel particles. Test results indicated that a perforated base pedestal with uniform voids simulated a rounded, uniform, coarse-grained gravel subgrade in terms of internal erosion. The hydraulic heads that caused internal erosion were similar when a perforated base pedestal or a rounded gravel subgrade was placed beneath a GCL. When the same GCL was used over a base pedestal or over a gravel subgrade with equivalent void size, the difference in hydraulic heads at failure did not alter more than 5 m, except for one comparison. For most of the tests, the performance of the GCL placed over the gravel subgrade was slightly better than that of the perforated base pedestal in terms of internal erosion. These results indicated that the proposed technique of using perforated subbase to simulate gravel remains conservative for the GCLs and gravel subgrades considered as part of this study.