Study On The Mechanism Of Loess Landslide Induced By Earthquake In Yuanzhou District Guyuan City

In Yuanzhou district，1920Haiyuan earthquake induced a mass of seismic landslide，causing great casualties and huge property losses.With the aim of finding out the basiccharacteristics，formation conditions and development rule of geological disasters in thisarea and proposing scientific and reasonable control measures against the hazard，we needto study the formulation mechanism of this landslide，analyse and evaluate its currentstability.On the basis of a detailed survey of the geological hazard in Yuanzhou District, thispaper employs technical methods such as crime scene investigation, laboratory test, andnumerical simulation to investigate the formation mechanism of two typical loesslandslide triggered by earthquake—the one caused by seismic liquefaction and the onecaused by seismic force. And the results are:(1) The landslide in Yuanzhou District induced by the1920Haiyuan earthquakecan be divided into two types on the basis of trigger mechanism—the one caused byseismic liquefaction and the one caused by seismic force. The former, featuring low angle,high speed and long-distance sliding, mainly distributes in the transitional zone of riverterrace and loess platform; the latter, featuring high speed, collapse and slide, centrallydistributes in loess hilly region.(2) The common slope made up by loess and mudstone in In Yuanzhou district mayproduce massive landslides easily, if the gradient of slope is above30°and the seismicintensity is higher than Ⅷ.(3) Through discrimination of liquefaction possibility and numerical simulationanalysis,the results showed that the shibeiyuan landslide is formed because the fine sandlayer of overlying malan loess is caused into liquefaction during Haiyuan earthquake andthen the sliding mass slide along the liquefaction zone under dead weight and seismicexcitation.The landslide whose sliding distance is1.2km and sliding velocity is6.6m/s istypical one of low angle,high speed and long distance. (4) Through analyzing the result of numerical simulation of the original slope ofshuiquan village2ndgroup landslide,we think that the loess slope is in stable positionbefore the earthquake.The direct reason of the large scale slipping along the contactbetween loess and mudstone is the great earthquake force of Haiyuan earthquake. Theformulation mechanism of this kind is seen frequently in loess seismic landslidedistributed in the east and northeast of yuanzhou district.