An experimental study on water and sand leakage disaster of gap-graded sandy soil under different grain size distributions

Water and sand leakage (WSL) disasters frequently occur in underground engineering such as tunnels and foundation pits. The appearance of leakage port destroys the stable soil structure and leads to the leakage of soil particles in large quantities under the action of water flow and gravity, especially in gap-graded sandy soil layer. Therefore, model experiments on the WSL of gap-graded sandy soil with different grain size distributions are conducted by self-designed WSL simulation device. Moreover, the applicability of Peck curve and ellipsoid theory in estimation of the volume loss rate and influence radius of WSL in sandy soils is explored. Results show that GGS1 containing 20% coarse particles fails to form soil arch with 80.7% of sand leaked. However, GGS2 and GGS3 containing 40% and 60% coarse particles form soil arches in WSL with 13.5% and 10.9% of sand particles leaked, respectively. Moreover, the soil surface settlement decreases, while the settlement influence radius increases, as the content of coarse particles increases. The natural filter channel formed in sandy soils with higher coarse particle content is longer and wider. Finally, theoretical results are consistent with experimental results, which verifies the applicability of Peck formula and ellipsoid theory in the evolution of WSL.