The Research On The Formation Mechanism Of The Typical Landslide In Yan'an Area

Situated in the middle part of loess plateau,Yan'an has many loess landslides.According to a general survey of geologic hazards in Yan'an district,the number of loess landslides amounts to 1350,almost all of which are loess landslides.There are different incentives bringing about the landslides.Some are from natural causes such as rain and river erosion while others from human activities such as construction excavation and loading,reservoir water retaining,etc.Different incentives produce different mechanism for landslides,which demands prevention and harnessing measures.Therefore,a good research on mechanism of producing landslides from different incentives in Yan'an will provide theoretical basis and technical support to take precautions against landslides calamity,which will be of a great help to make a practical and feasible plan for prevention and reduction of natural disasters,avoidance or reduction in property loss and casualties.In this paper,the author has adopted various methods such as analyzing the existing data,surveying the field sliding elements,sampling and testing typical sliding sites,testing rock and soil in lab,and numerical simulation,etc.to analyze the very mechanism of inducing landslides.What follows are what has been done and achieved.(1)The author has summarized the development types of landslides in Yan'an on the basis of statistics on and analysis of the detailed results of geologic survey;and detected the major controlling causes and incentives of landslide growth in this area.(2)In light of growth conditions of the old and fresh landslides in Yan'an,direct shear test of remodeled saturated loess and shear test of undisturbed loess in three axis conditions are separately carried out to gain strength characteristics of remodeled saturated loess and undisturbed loess.Meanwhile,a uniaxial compression test and a compression test for mudstone and sandstone in this area are conducted.A “rebound test” is implemented to analyze the strength of the sandstone surface structure.(3)On the basis of analyzing rainfall infiltration method and law and by means of numerical simulation,the author takes Jizixian Town landslide in Fuxian county,Yanjiagou landslide and Yan'an Refinery landslide as typical examples to reproduce thevivid process of causing various landslides when rain infiltrates through the joints of the loess porosity,flows through centralized channels such as unloading cracks and sinkholes,etc,and migrates gradually through water gaps.The paper deals with the formation mechanism of different landslide because of different infiltration methods.(4)Based on Anli landslide,Yintaishan landslide and Luochuan gas station landslide,numerical simulation method was used on the analyzing of different landslide processes,including head erosion,river side erosion,river erosion and gully erosion.Through comparing the changes of sliding surface stress and shear strength in different stages,the formation principle of landslide was well explained.Landslide trends simulation makes sliding range and movement distance obtainable.(5)According to the feature,conceptual model of upstream slope for the reservoir,this thesis illustrated the landslide mechanism for upstream slope of the reservoir by numerically simulated the change of the corepower pressure and shearing strength,analyzed the relationship between the shearing strength and shearing resistance,and found out the change of the stability for downstream slope.Furthermore,took the Zhaojiaan as an example of the downstream slope landslide,this thesis illustrated the landslide mechanism for downstream slope of the reservoir by simulated and analyzed the change of corepower pressure and the stress while the water level rose or fell.(6)Based on Sanmutai landslide,Nanyaocun high slope and Longshoucun high slope,numerical analyzing method was used on the explanation of fresh landslide formation principle,which was a result of artificial excavation.Based on wangyaocun landslide,old landslide reviving principle was revealed,which was a result of artificial excavation.Based on Yuanhezhuang landslide,the changes in slope stress and shear strength were analyzed,and the surface loading landslide formation principle was explained.