Early Identification And Danger Prediction Of Loess Landslide

Heifangtai region located in Yongjing County in Gansu Province,a typical area of loess landslide induced by irrigation,has become one of the most frequent geological disasters on the Loess Plateau and even in China,which seriously restricted the social and economic development.However,the practice of the spatial prediction of landslide based on regional scale in this area bear two defects,the lack of early identification of landslides based on quantitative assessment of regional stability and prediction methods about hazard ranges after landslide.In order to provide more reliable quantitative basis for risk management,and to promote the development of spatial prediction of loess slope,and further to provide theoretical basis and practical guidances for constructing the efficient and reliable regional monitoring and early warning system.Taking Heitai irrigation district as a case,the paper firstly used time series InSAR(Synthetic Aperture Radar Interferometry)technology to monitor surface deformation,analyzed the deformation characteristics,and identified the landslide in the early stage;Secondly,a quantitative model based on physical and mechanical process was established to evaluate the sliding probability of potential landslide.Lastly,the prediction method of landslide volume and sliding distance was carried out to obtain the range of potential landslide.The following research results were obtained:(1)62 landslides are catalogued in Heitai tableland,of which 12 are loess-mudstone landslides,large-scale and close-sliding.And the other 50 are pure loess landslides,which can be divided into shallow landslides,loess remote sliding and loess earth flows,according to the motion characteristics.The occurrence of these three landslides has a sequence,usually the shallow landslides staggered in the first,and transformed into loess earth flows in the last.The topographic analysis shows that Jiaojia section has experienced frequent landslide activities in the past,but it has tended to be stable in recent years.Whereas,Dangchuan section and Moshi valley section has begun to become active and is continuously active(2)The time series InSAR technique was used to obtain the surface deformation of Heitai irrigation district during 2014-2017.Combined with field investigations,it is proved to be of high applicability for regional deformation monitoring.The results show that:the surface deformation is still very dramatic,mainly concentrated in the southwest of platform,as Xinyuan Village,and the slope sections,as Dangchuan,Moshi valley and Yehu valley.The southwest dominated by uneven subsidence and the deformation of slope sections are characterized by the collapses,cracks and the multi-stage slidings.The deformation informations of DC03,DC04 and DC05 before sliding are captured and the deformation rate is-40~64mm/yr,which provides a reference for the potential landslide cataloguing.At the same time,considering the characteristics of terrain,geomorphology and disaster environment,43 unstable slopes have been identified.(3)In order to quantitatively assess the instability of potential landslide and improve the research about quantitative evaluation in this area,physical and mechanical model of Scoops 3D was established.In historical evaluation results,more than 80%of the landslide has been accurately calculated,and the model has the capacity of reflecting the stability status to some extent.The evaluation results about present situation show:31.43%of the regional F_S(safety factor)is still below 1.2,distributed in Dangchuan section,Yanji section and Yehu valley.There is 26 out of 43 potential landslide that F_S is below 1,which is in high risk.Although the deformation in Huangzi section and part of Moshi gully is active,the F_S of those potential landslide there is above 1.5.It can be concluded that the probability of converting into landslide is low and the slope would be local deformation in future.The differences of regional stability are closely related to the evolution of free surfaces and cracks dominated by variation of the groundwater.After years of landslide,the disaster environment of Jiaojia has been improved significantly,but the Dangchuan section still be in poor condition for developing landslide,so stability is also very poor.(4)In addition to evaluating landslide prone areas and delineating potential landslide,hazard range prediction is also important for spatial prediction.Based on potential sliding source area and analysis of movement process,the empirical formula of source area and volume is established:V-0.0045S~2+1.7812S-1.7668.Moreover,The multiple linear regression model is selected to establish the sliding distance empirical formula of different types,after selecting the key disaster factors.The volume and sliding distance of 43 potential landslides are calculated.The danger in Dangchuan section is especially serious and preventive measures need to be taken.