Study On The Unsaturated Permeability Test Of Undisturbed Loess And The Irrigation Infiltration Law Of Jingyang Slope

Loess landslides are the main geological disasters in the Loess Plateau and pose a great threat to the safety of human life and property.Water infiltration such as rainfall,irrigation and snowmelt is the main cause of loess landslide induced.In order to study the change law of pore water pressure caused by water infiltration of unsaturated loess slope and reveal the landslide mechanism,this paper takes L1,L5,and L9 undisturbed loess in Jingyang as the object.Based on testing its basic physical indexes and saturated permeability coefficient.the particle size distribution is measured with a laser particle size analyzer,the pore distribution is measured with mercury porosimetry,and the soil-water characteristic curve(SWCC)is measured with a filter paper method.Combined with the transient profile method and filter paper method,the method to determine the unsaturated permeability coefficients and the matric suction is independently developed.The method is used on L5 loess.The following results are obtained.There are two dominant peaks in the grain size distribution of loess.The grain sizes are about 25mm and 0.7mm,respectively.During the period,there is a valley with a lack of grain size.The grain size is about 2.0 m m.There are also two dominant peaks in the pore distribution,which were about 5.0 mm and 0.03mm.The complete soil-water characteristic curve of loam 1-100 000 kPa is measured by filter paper method.The Gardner(1958)model,Van Genuchten(1980)model and Fredlund & Xing(1994)model are used to fit the SWCC of the three-layer soil.The air-entry value,residual moisture content,and related parameters of each model are obtained.The Fredlund & Xing(1994)model is considered to have the best fit.Using the self-developed unsaturated permeability coefficient measuring device,the effects of the measurement time interval and section interval of the transient profile method on the estimation of the unsaturated permeability function of loess are studied in detail.The SWCC is divided into saturated zone,the first liquid water migration zone,the the second liquid water migration zone and the gaseous water migration zone.It is considered that it is necessary to ensure that the soil moisture content in the infiltration process is in the same area when calculating the section interval and time interval.The improved Childs & Collis-Geroge method and the Fredlund & Xing model are used to fit the SWCC equation.The permeability coefficient is estimated and compared with the measured value.It is considered that the estimated value is large under the suction of the matrices less than 100 kPa,and the test value and estimation under high suction are considered.The values are more consistent.Chosen k=a(?) as the permeability functionof the loess and combined the saturated permeability coefficient and the air-entry value of the SWCC,the parameters are estimated.A geological model is established using Shutangwang Slope of Jingyang,and the SWCC,the permeability function and the shear strength measured by the consolidated undrained test are used as input parameters.And this paper calibrates the flow boundaries in the model based on the known condition that the stability factor of the slope slip occurred on October 2,2002 is1.And then the influence of irrigation distance on the pore water pressure in the slope and the influence on the slope stability are studied.