Study On Unsaturated Infiltration Characteristics Of Losee In Hei Fangtai,Gansu Province

The loess is widely distributed in China,accounting for 70%of the total amount of loess in the world,especially in the northwestern region.Based on the fragile geological environment,coupled with the rising water table caused by perennial irrigation,the landslides are frequently generated in this area,which seriously restricts the development of the local economy.Thus the study of loess infiltration are of great significance for clarifying the mechanism of loess landslides.This paper takes the Heifangtai loess landslide as the research object,comprehensive field investigation and literature survey methods were carried out to study the unsaturated infiltration characteristics of the Heifangtai loess.Field investigations,large-scale soil column tests,theoretical models based on experiments,and numerical simulations were used to deeply analyze the infiltration characteristics of the Heifangtai loess.The following conclusions were obtained:(1)Large-scale indoor soil column tests,The fractures were mainly distributed within 30-100cm,with agglomeration.The maximum settlement is 4cm,and the position of maximum settlement is at 106cm.Crack development is mainly above the maximum settlement.(2)Both the infiltration depth and cumulative volume of infiltration water gradually decreased,and the trends of the wetting front migration rate curve and the water accumulation rate change curve were similar.According to the change of infiltration rate,the infiltration process can be divided into three stages:A water strength control stage,B non-saturation infiltration stage,C saturated infiltration stage.The soil below the maximum settlement is a continuous and uniform settlement with a sedimentation rate of about 0.9 cm/d.The settlement of loess is linearly related to the depth.The settlement of loess(collapse capacity)is 2.19 cm/m,and the dry density increased from 1.42g/cm~3 to 1.45g/cm~3 during the infiltration settlement of loess.(3)The volumetric water content of the loess increases first and then decreases and finally maintains stable.The change trend of the moisture content response time is basically consistent with the migration trend of the wet front.According to the moisture conten profile of the soil column,it is divided into three infiltration stages:the initial stage of water control,the non-saturated migration period,and saturation stability stage.(4)The matrix suction decreased rapidly with the infiltration of water.The leachate flow decreases gradually with decrease of water head and the extent of decline increases gradually increasing.Particles with particle sizes between 2.2um and 28um exhibited significant changes with infiltration content.The increase in the content of cohesive particles and powder particles had a certain influence on the infiltration rate.(5)According to the characteristics of moisture content change in the test and combined with the actual moisture content profile in the field,a generalized infiltration model for loess was established.The infiltration of loess is mainly water-gas migration,which is a typical non-saturated stable infiltration.(6)Based on Garder model,van Genuchten model and Fredlund&Xing model,the measured matric suction and volumetric water content were fitted.The correlation coefficient R~2 of each model was 0.9894,0.9913,and 0.9916.The value of the G-A head infiltration model obtained by map method is 0.0004 cm/min and 12.18 cm.Corrected G-A infiltration model.it was found that in the shallow surface infiltration of loess,the model has a good agreement.With the increase,the fit of the model gradually decreases with the increase of infiltration depth.(7)Hydrous-1d software was used to simulate the relationship between water content and profile depth.The simulated values and experimental measured values were basically consistent.The actual geology of loess landslides was analyzed.The loess seepage field changes during the 100-day cycle of irrigation was simulated using geo-studio software.Simulation results show that the simulation results are in good agreement with water level monitoring data,and the water head value at the infiltration near the slope is increased,which cause groundwater fluctuations.By comparison of water level before and after infiltration.In the 100-day cycle,the water level of the slope model was raised by 0.12m,and the groundwater level was raised by 0.15m,the increase was basically consistent.