| In this paper,the rainfall-type loess slope was taken as the research object.The engineering geological survey,mapping,in-situ monitoring,sampling and laboratory tests were carried out on Pijiagou Slope,Baota District,Yan'an.The basic physical properties,soil-water characteristics and strength characteristics of unsaturated soil of Malan loess were obtained.The data of rainfall,ground temperature and water content in the study area were gained.The infiltration rule of rain in loess slope and the influence of different factors on the water content of the slope were studied.Moreover,a prediction model of water content of the slope under rainfall was established by using the neural network.On this basis,according to finite element analysis of saturated-unsaturated loess,the influence of rainfall on slope stability was discussed.The conclusion is as follows:(1)The soil-water characteristic curve(SWCC)and hydraulic conductivity function(HCF)of undisturbed Malan loess in study area were measured by using the transient release and imbibition method(TRIM).The path of dehumidification curve and moisture adsorption curve is obviously different,and hysteresis effect between them exists.The soil-water characteristic curve and hydraulic conductivity function under dehumidification and moisture adsorption are similar,and the trend of change is consistent.The suction stress and matric suction under dehumidification are greater than that under moisture adsorption.(2)The shear strength of unsaturated undisturbed loess in study area was measured and calculated by direct shear test.With the increase of matric suction,the cohesion of undisturbed loess in study area increases linearly,while the internal friction angle remains unchanged.The suction internal friction angle(?~b)linearly decreases slowly with the increase of matric suction when matric suction was 0–200 kPa.The?~b is constant less than the effective internal friction angle which is 30.2°.(3)According to in-situ monitoring of rainfall infiltration on slopes,the law of rainfall infiltration on loess slopes and the influence of different factors on water content of slopes were studied.The threshold of precipitation causing suddenly increase of water content is22 mm/d.The change of water content in the shallow surface of slope is larger during summer and autumn when the rainfall is more.During periods of concentrated rainfall,with the increase of depth,the increase of water content decreases gradually,which has a lag effect.The maximum impact depth of rainfall in study area is not more than 4m.The closer the soil is to the surface,the earlier and faster the change of soil water content under rainfall conditions.When the depth of soil exceeds 0.6m,the decreasing rate of rising range of water content begins to decrease and tends to be fixed value.The larger the slope,the longer the response time of soil water content,the smaller the rising range of water content,but this phenomenon has little influence on the soil water content of slope surface.The maximum infiltration depth of rainfall and slope decrease exponentially.Both rainfall intensity and duration can increase the average rising range of soil volume water content.Neural network can be used to establish prediction model of water content of slope under rainfall conditions.(4)The finite element model of saturated-unsaturated loess and stability analysis model of unsaturated loess were established to analyze the seepage law of slope and its influence on slope stability under different rainfall duration,slopes and infiltration modes.When joints and fissures do not exist in loess slope,short-term and long-term rainfall have little effect on seepage field and stability of slope.The dominant channels such as joints and fissures have great influence on the pore water pressure of the slope,and the slope stability decreases obviously.When the rainfall conditions are constant,the stability coefficient of slope does not continue to decrease with the increase of slope. |
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