Abstract: A case study is conducted on a foundation pit in Nantong, China, to investigate the mesomechanism of ground collapse induced by the leaking of underground diaphragm wall in waterrich sandy strata. In addition, the evolution law of the ground collapse is analyzed by computational fluid dynamicsdiscrete element method and related countermeasures are discussed. The following results are obtained: (1) The included angle between the boundary line of the influenced zone and the horizontal line is approximately (45°+〖WT〗φ/2)〖WT５《TNR》〗 in the case of an underground diaphragm wall. The value and growth rate of ground collapse increment induced by the leakage are large and within〖WT〗 1HL (HL〖WT５《TNR》〗=leakage depth) behind the underground diaphragm wall. (2) During the leak, the ground cavity undergoes generation, expansion, and collapse stages and rapidly collapses with ground settlement. (3) Active earth and water pressure near the leaking point increases by 5.7 to 8.5 times compared to that observed in the model with no leakage. This increase is large when leakage occurs at or above the excavation surface. Underground diaphragm wall leaking may lead to structural cracks, abrupt ground subsidence outside the pit, and the kicking damage of the retaining wall.

Key words:  , foundation pit, waterrich sandy strata, underground diaphragm wall leaking, numerical simulation, ground collapse