EXPERIMENTAL STUDY ON MECHANISM OF FLOW SLIDE OF LOESS LANDSLIDES TRIGGERED BY STRONG EARTHQUAKE——A CASE STUDY IN DANGJIACHA, NINGXIA PROVINCE

This paper aims at the problem of low angle and long distance fluidized loess landslide triggered by earthquake. It takes the Dangjiacha landslide as a typical example. It was triggered by Haiyuan Earthquake in 1920. A detailed field investigation and indoor research are carried out for the Dangjiacha landslide. After comprehensive analysis, it reveals the genetic mechanism and movement characteristic of Dangjiacha landslide. In the earthquake process, the original structure of Ma Lan loess was destroyed destructively. The upper unsaturated loess was damaged in tension with the seismic shaking. Edge cracked, excess pore water pressure was accumulated in saturated zone. The saturated loess was liquefied and plastic deformation had accumulated. The shear surface gradually transfixed. Under the seismic horizontal ejection, the slope collapsed in high-speed. Three sliders slid to the middle groove, along the direction of 295 degree, 300 degree and 80 degree to the north respectively. Then they turned down the ditch with collision. Liquefied layer flowed forward like mudslides, showing a typical "the shear-thinning fluid", with extremely low steady-state strength and very low apparent dynamic viscosity coefficient. The upper loess floated with low angle and long distance movement, finally rushed out the valley, then turning along Bao Yu Gou to downstream for the mountain barrier. The displacement was up to 3 km. The results have important reference value or guiding significance for further understanding the formation mechanism of fluidized loess landslide under strong earthquake conditions and preventing geological disasters triggered by earthquake liquefaction in loess area.