Abstract: It is shown that the water tables of leachate in many early valley-type MSW landfills in Chinese Southern Region are very high by the operating experiments in last ten years. It is shown that the high water table of leachate by rainwater infiltration is a main factor induced MSW landfill landslide by many literatures. So, it is very important to investigate the water transport responses and the stability of valley-type MSW landfills under heavy rainfall. Firstly, based on the soil-water characteristic curve of shallow, middle and deep layer MSW in Qizhishan landfill and Brooks-Corey equations, the permeability function of MSW landfills is given by nonlinear curve fitting. Secondly, numerical analyses are conducted to investigate water transport in Qizhishan valley-type MSW landfill subjected to rainfalls with four different patterns, i. e. delayed, central, advanced and uniform rainstorms. At last, the stability of Qizhishan landfill has been studied by limit equilibrium method. The computed results show that rainfall pattern has a significant influence on water transport in valley-type landfill and its stability, and the delayed rainfall is found to be the most critical one because it results in the highest pore-water pressure in the landfill and the smallest safety factor of landfill. Numerical results show that the safety factor of landfill reaches 1.016 after 746 mm rainfall with duration of 7 days, and the possibility of landside in Qizhishan landfill is very great.

Key words: Qizhishan landfill, rainfall patterns, rainfall infiltration, saturated-unsaturated seepage, water transport, stability analysis