Study On The Irrigation-induced Loess Landslide Mechanism With Centrifugal Modeling Test

In our country,loess area is mainly distributed in the northwest arid and semi-arid region,with reduced rainfall and lack of water resources.In order to solve irrigation problems of agriculture,a large number of irrigation facilities were built in recent years.Under the effect of long-term irrigation,region groundwater balance suffered damage.The role of groundwater in slope resulted in softening of rock and soil mass,reduces the strength of the loess and the slope foot support.This caused a large number of loess landslides.In Heifangtai area,after artificial large-scale irrigation since 1968,with the increasing irrigation,the ground began to produce a large area of subsidence deformation and the loess collapse,have occurred in dozens of large-scale landslide,formed large landslide group around with the Heifangtai loess platform.In this paper,based on the Jiaojia No.13 landslide in Heifangtai area,centrifuge model tests were conducted to research on irrigation induced the loess landslide.The main conclusions as follow:(1)Jiaojia No.13 landslide is a typical irrigation-induced landslide in loess layer.A total four layers of strata in this area,in the order: loess layer,silty clay layer,sand and gravel layer,sand shale interbed layer.After irrigation,the water flowed downward along the vertical fissures of loess layer.After obstructed by silty clay layer,the water began to accumulate at the bottom of the loess layer.The water table began to rise gradually,forming a layer of saturated and softened zone in the bottom of the loess layer finally.(2)Water have great effects on mechanical properties of loess.Some tri-axial tests were carried out herein to analyze soil hydro-physical properties and soil shear strength for malan Loess.The results show that the shear strength of loess decreased with water content,when the water content is larger.(3)Based on the Jiaojia No.13 landslide,the deformation-sliding process of the loess landslide is stimulated at the acceleration of 200 g by the 500 g.t large geotechnical centrifuge.The centrifuge model is made of the undisturbed loess.Groundwater applied through the customized waterproof shield and the water tank.(4)Through centrifuge model test,from the deformation-sliding process of the loess landslide,the deformation and breakage of bedding slope firstly arises at the foot of the slope after the groundwater discharge from here.Damage area gradually expands upwards,loess slumping at the top of the slope.With the development of landslide process,the slide slip plane is a circular slip.(5)First the unsaturated and unsteady seepage analysis is made on the slope under the condition of irrigation.by means of Seep/W software.The paper deals with the law of ground water movement in the slope and calculating seepage lines of underground water in loess slope by different degrees of irrigation.Based on FLAC3 D numerical simulation,the stability of loess landslide is studied by through the simulation of different irrigation periods and different irrigation water supply conditions.(6)Combined with the theory to analyze,we perform numerical simulations and the centrifuge model test to simulate the process of four movement stages of loess landslide,such as,saturation and softening stage,peristalsis-tensile stage,sliding-failure stage,headward-erosion stage.The deformation mechanism of irrigation-induced landslide in loess layer belongs to creep sliding-tension type.With the continuous development of the landslides,crown of landslide continued move to the loess platform center.