Examining the criteria for contact erosion in granular soil foundations through transparent soil model tests

Abstract

Contact erosion, or interfacial erosion, often occurs in layered foundations composed of coarse and fine layers, which refers to the phenomenon that the particles of the fine layer are detached by the flow parallel to the interface and transported through the pore channels of the coarse layer. In order to visualize the initiation and progression of contact erosion at the internal interface of soil strata, the transparent soil model tests were employed to simulate the real soil, and a series of contact erosion tests were conducted on double-layer foundations composed of different coarse and fine layers. Based on the test results, the commonly used geometric and hydraulic criteria for contact erosion were examined. It shows that the geometric criteria are reliable, while hydraulic criteria give much diverse results. For the same fine soil layer, the critical hydraulic gradient varies greatly with the coarse soil layer, while the critical flow velocity varies in a relatively small range since flow velocity has an intrinsic relationship with the dragging force imposed on particles by seepage flow. It is suggested that more efforts should be paid to the criteria based on critical velocity in further studies for contact erosion.