Abstract: Because the studies on the occurrence mechanism and collapse mode of slurry trench during the construction of underground diaphragm wall in heterogeneous and water-rich stratum are rare, a discretization three-dimensional failure mechanism of slurry trench is established by using the spatial discretization technique. Based on the proposed mechanism and the upper bound theorem of limit analysis, an objective function for the safety factor of the slurry trench is obtained by introducing the heterogeneous characteristics of soil and pore water pressure into the energy dissipation calculation. The optimal upper bound solution for the safety factor of the slurry trench is calculated by the nonlinear programming approach. To verify the validity of the proposed method, the safety factors of the slurry trench are compared with the results of the existing documents and the solutions provided by the numerical simulation technique. Moreover, the comparative results show that the calculated safety factors are in accordance with those of the existing documents and numerical simulations. The parametric analysis shows that the heterogeneous characteristics of soil and pore water pressure affect the safety factor of the slurry trench. The safety factors of the slurry trench decrease with the increase of the cohesive inhomogeneity coefficient k_c and underground water level H_w, and increase with the increase of the unit weight inhomogeneity coefficient k_g.