Abstract: Through field investigation and lab analysis, computation models of landslides with topographic hollows in Ziyang county of the Qinling-Daba Mountains were set up based on unsaturated soil mechanics theory. The stability and seepage with saturated and unsaturated properties under transient conditions were computed by limit equilibrium method in consideration of pore water pressure and unsaturated strength. Results show that topographic hollows induce slope failure through convergence of subsurface flow into small areas in the slope. Per unit depth of the maximum pore water pressure measured in an area close to the base of topographic hollows was found to be higher with bigger topographic hollows. Furthermore, a threshold relationship between the topographic hollow area and maximum pore water pressure in this study indicates that a topographic hollow of 1 000 m² area could generate a maximum pore water pressure of 1.47 kPa.

Key words: shallow landslides, topographic hollows, Qinling and Daba Mountains, pore water pressure, factor of safety