Examining the criteria for contact erosion in granular soil foundations

Abstract

Contact erosion, or interfacial erosion, often occurs in layered foundations composed of coarse and fine layers; it 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. To visualise the initiation and progression of contact erosion at the internal interface of soil strata, transparent soil model tests were employed to simulate real soil, and a series of contact erosion tests was 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 is shown that the geometric criteria are reliable, while hydraulic criteria give 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. More efforts should be invested on the criteria based on critical velocity in further studies of contact erosion.