111 Influences of Underground Drainage and Rainfall on the Stability of a Landslide

The special location of Dayan tang landslide makes it affected by the engineering construction more severely. Some horizontal drainage tunnels are dug beneath the slip belt to enhance the stability and prevent the failure of the landslide during the construction period. The stability of the landslide will be impacted by the heavy foggy rain formed by flood discharge when the hydro project begins operation. A secondary improvement has been done for FLAC program to simulate the infiltration and a three dimensional analysis has been accomplished coupled the soil mechanism with infiltration of rainfall. Conclusions are obtained as follows: firstly, the saturation time of the landslide caused by foggy rain is 1∼2 days. Secondly, the accumulation of the over pore pressure in the slip belt is delayed or mitigated for the existence of the drainage tunnels underground and the gravel clay on the surface. Finally, the stability factor is decreased more than 20% and the main broken area takes place at the front and middle part during the foggy rain period.