Mechanism Of Irrigation-Induced Loess Landslide At South Jingyang Plateau

In Jingyang Southern tableland,the loess landslides occurred frequently,which seriously threatened the life and property safety of local villagers.The field investigation shows that the loess landslide in this area is significantly affected by agricultural irrigation,and it belongs to irrigation-induced loess landslide.This paper takes the loess landslide of Jingyang South tableland as the research object,and analyzes the characteristics of loess landslide in the area on the basis of field investigation.On this basis,the macroscopic mechanical and microstructure characteristics of Q2 loess in the region were studied by conventional triaxial test,CSD stress path test and soil-water interaction characteristic curve test.The effects of different irrigation conditions on slope stability were simulated by using Geoslope software.Finally,the mechanism of loess landslide induced by irrigation in Jingyang south tableland is discussed.The research results have certain guiding significance for deepening the mechanism of irrigation-induced loess landslides and coordinating the prevention and control of geological disasters.The main research contents and conclusions are as follows:(1)Loess landslides in the study area are distributed along the edge of the tableland,and four landslide groups are developed,namely Jiangliu,Shutang,Zhaitou and Miaodian.With the increase of sliding order,the volume of the landslide decreases gradually,the position of shear outlet increases gradually,and the sliding distance becomes shorter obviously.According to the movement characteristics,irrigated landslides in the area are divided into two types:flow slide type and slide type.The slide distance of irrigated slide type is about four times of the slope height,and the slide distance of irrigated slide type is about two times of the slope height.(2)The physical and mechanical test of Q2 loess in the study area was carried out.The results showed that under the conventional triaxial test condition,the sample showed the characteristic of "strain softening".The softening degree of soil decreased with the increase of confining pressure.Under the condition of constant shear stress drainage shear test,the failure of the sample can be divided into supercharging peristaltic stage and liquefaction dynamic stage.Based on the soil-water interaction characteristic curve test of unsaturated loess,the variation rule and difference of matric suction and permeability coefficient during dehumidification and hygroscopicity were given.(3)SEM and NMR experiments were carried out on the samples before and after the drainage shear test with constant shear stress.The results showed that before the shear test,there were a large number of individual debris particles in the samples,which were mainly connected by cementation,and there were pores of different sizes in the soil,mainly large and medium ones.After shear,the monomer particles of soil decreased and appeared obvious granulation.The contact relationship of particles changed to contact connection,and the total volume of pores in soil was significantly reduced compared with that before shear and mainly consisted of micro and small pores.(4)The influence of different irrigation conditions on slope stability was simulated by using the software Geoslope.The simulation results showed that the slope stability coefficient decreased with the increase of irrigation time under all irrigation conditions.When the amount of irrigation is controlled,the slope stability coefficient increases with the increase of irrigation range.When the irrigation range is controlled,the stability coefficient of slope decreases with the increase of irrigation amount.(5)The mechanism of the loess landslide induced by irrigation in jingyang Southern tableland was as follows:agricultural irrigation led to the rise of groundwater level,the increase of loess saturation at the foot of the slope,the decrease of matric suction and shear strength of the soil,and the slight deformation of the slope and the formation of creep shear plane inside the slope.With continuous irrigation,slope toe saturated soil lager thickening,further reducing the shear strength of soil,grain shear deformation has caused soil slope sliding pore filling body pore water drainage channels blocked,pore pressure rise form the static liquefaction,undrained shear which happen in a short period of time,the deformation increases rapidly,sliding surface,the integral sliding slope.