Study On The Mechanism Of Dujiangyan Landslide Movement

In early July, 2013, Dujiangyan city of Sichuan province began to encounter extreme weather for several days. Rainfall reached 415.9mm only from 20 pm in the 8th to20 pm in the 9th. Due to continuous heavy rainfall, a large-scale geological disaster suddenly occurred in high position on the wulipo village of Zhongxing town at about 10:00 am, July 10, 2013. The whole volume of landslide wasmore than 1.5 million m3, out of the high positionof wulipo along the trench filled river and riverbed elevation. Alluvial materials impacted to both sides of the channel directly and buried the channel, resulting in the buried area reaching about 0.3km2.The No.1 landslide-debris run-out distance is 1.26 km, which caused 11 households destroyed,52 villagers and Nongjiale tourists were dead, 109 people missing. Therefore, the analysis of the effect of deformation and failure evolution of the disasterand mechanism of typical lands lides occurred in the heavy rainfall is of great theoretical and practical significance.This paper took the large landslide in wulipo village of Zhongxing town of Dujiangyan city of Sichuan province for example. Through field investigation, the model of the typical shape of the slope to be generalized and transported into the MIDAS/GTS finite element numerical simulation analysis software to establish three-demission geological model. Then, using FLAC3 D software the finite difference to established slope rainfall analysis model. Secondly, the physical and mechanical parameters of the simulation numerical of rock and soil, rock mass and weak interlayer of slope were determinedthrough physical lab of field sampling. Finally, simulations under different daily rainfall were conducted to obtainslope internal displacement and pore water pressureunder the heavy rain and the instability mechanism by analyzing the tracking and monitoring of local special point of bedding rock slope under rainfall. The results showed that below:(1) The rainfall seepage in the rock field formed the hydrodynamic and hydrostatic pressure. Hydrodynamic and hydrostatic pressure as the external forces exertedon the slope, increased the sliding force of slope, so as to influence the stability of the slope.During the rainfall infiltration process, along with the rainfall intensity increases, the displacement of the slope body was increased and reduced the overall slope stability.(2) The long time continuously extreme heavy rainfall was the direct reason triggering the large-scale landslideof wulipo village of zhongxing town. The study ofnumerical simulation of the process found the phenomenon that the slope of wulipo village of zhongxing townin long duration rainfall developed cracks at the top of the slope and vertical in slope under the shattered or damaged effect induced by the Wenchuan earthquake, extending to the level of free surfaceand along the rock fracture surface. Rock cracks formed a deformed body of many sets of large structural planes separated in space. Under continuous heavy rain, the powerful rain infiltrationproduced a lot of pore water pressure andthen made the top of slope out of balance. That is to say, push rock landslideoccurred starting moving from the back of the slope.(3)At the beginning of the rainstorm, the pore water pressureincreased at fast growth rate. The pore water pressure of the slope surface descended in order of the slope in rear middle and front, so as well the relationship with the slope displacement. But the development models of pressure and displacement are different from monitoring. It can be found that the changing turning point of two variable were not the synchronous from the process. The variation of pore water pressure began at first andthen the displacement. It also showed that the slope near the upper where excess pore water pressure accumulated adjustedand redistributedthe slope stress, causing obvious displacement changes. Later the development trend of pore water pressure has been unable to reveal or forecast the slope displacement.(4) The numerical slope displacement increase of weak interlayer speed lagged behind the corresponding values of slope surface under rainfall condition. It reflected that rainwater seepage entering from the slope surface to inner slope tooksome time to achieve. With the continuous rainfall, displacement growth gradually accelerated and the weak interlayer was sliding obviously characteristics at the end.