Permeability and Internal Erosion Responses of Gravelly Soils Following Slurry-Induced Clogging

Abstract

Bentonite slurry is used to maintain trench stability during cut-off wall construction. Because the slurry level remains above the groundwater table, slurry can infiltrate the surrounding soil and form a spatially heterogeneous clogging structure within the pore network. In this study, field excavation of an experimental cut-off wall was conducted to observe the slurry infiltration into the surrounding soil. A large-scale laboratory experimental apparatus was developed to reproduce the slurry infiltration into soil and test the seepage erosion resistance of the clogging structure. Field observations revealed a distinct interfacial filter cake and bridging zone in the soil adjacent to the wall, and grain size distribution analyses of wall-adjacent samples indicated an enrichment of fine material consistent with slurry intrusion. The laboratory results showed that the post-clogging specimens exhibited lower hydraulic conductivity and fines eroded ratios, together with higher progression hydraulic gradients, than the corresponding baseline specimens. However, no replicate tests were conducted, no water-treated process control was included, and no in situ permeability tests were performed in the slurry-affected soil. Accordingly, the results characterize the bulk hydraulic and erosion responses of internally unstable gravelly soils following support-slurry intrusion during cut-off wall construction, rather than the overall seepage performance of cut-off walls with explicit defects. The slurry-affected zone should therefore be considered in seepage analyses around local wall defects.