A Ring-Shear Radial-Seepage Apparatus for Evaluating the Permeability of Shear Bands in Compacted Clay

Compacted clay cores are extensively used in rockfill dams to cut off water flow because of their low permeability and wide availability. Large differential settlement often occurs at certain locations in a dam, causing large shear concentrations in the compacted clay core in the form of shear bands. This raises concern about the permeability evolution in the shear bands in compacted clay during a large shear process. Thus, a ring-shear radial-seepage apparatus was developed for evaluating the permeability of the shear bands in compacted clay. The apparatus tests hollow cylindrical specimens that are held in a shear box, which consists of an upper box, lower box, and inner chamber. The specimen is compressed in the height direction and sheared in the circumferential direction to form a concentrated shear band. The permeability of the shear band is measured by radial-seepage from the inner side to the outer side of the hollow cylinder. To demonstrate the performance of the apparatus, a series of tests was conducted on compacted specimens of a clay used for the core wall of a high rockfill dam. The test results showed that the change in permeability of the shear bands in compacted clay was dependent on the surcharge pressure. If the current surcharge pressure was far less than the preconsolidation pressure caused by the previous compaction process, the permeability of the shear band might increase significantly. This experimental finding can be useful for identifying high-risk leakage zones in a dam with a compacted clay core.