Rapid Measurement Method Of Hydraulic Conductivity Of Unsaturated Soil And Mechanism Of Landslide Induced By Rainfall Infiltration

Rainfall is an essential factor inducing landslides.To analyze the influence of rainfall on slope stability,we must analyze the law of water infiltration in the slope and reasonably consider the change of soil strength in the process of wetting.The unsaturated hydraulic conductivity is the most influential parameter in the seepage processAt present,there are two critical problems in the analysis of rainfall landslide:(1)because the "real value" of the actual soil hydraulic conductivity is unknown,the accuracy of the existing unsaturated hydraulic conductivity measurement methods is difficult to evaluate;(2)linear strength theory is often used in slope stability analysis at present,and the influence law of the nonlinear characteristics of actual soil strength on the stability of rainfall-induced landslide is unknown.In order to solve the above two problems,this paper first studies the measurement method of hydraulic conductivity of unsaturated soil through the numerical test,then analyzes the influence of unsaturated permeability characteristics on soil water infiltration,and finally calculates the stability of rainfall landslide considering the influence of nonlinear soil strength.The main research results of this paper are as follows:(1)An improved digital wetting front advancing method is proposed and compared with the traditional visual observation method.The results show that in the wetting front advancing method,the digital wetting front can be used to replace the wetting front observed by vision.Before the wetting front passes through the soil column device,the calculation of the advancing speed of the wetting front is not sensitive to the selection of the digital wetting front.Three monitoring sections are recommended to ensure the hydraulic conductivity’s accuracy.(2)The error sources and applicable conditions of the wetting front advancing method and instantaneous profile method are verified by numerical experiments.The results show that the wetting front advancing method has high accuracy in the high suction range,while the traditional instantaneous profile method has high accuracy in the low suction range.In the same soil column experiment,the digital wetting front advancing method is combined with the traditional instantaneous profile method to obtain unsaturated soil’s accurate hydraulic conductivity function under a wide suction range.This method is suitable for many soil types,and the test duration is only 1 ～ 5 days,so the measurement of hydraulic conductivity becomes a routine test of unsaturated soil mechanics.(3)The main controlling factors of the unsaturated infiltration process are studied.The results show that the seepage calculation in the h-form Richards form is suitable for both saturated and unsaturated soils,which has good applicability and is recommended to be applicable;the Unsaturated infiltration process has a high sensitivity to saturated hydraulic conductivity,initial conditions,and air-entry pressure.,and their accuracy should be ensured first in numerical calculation.(4)Through numerical experiments,the influence of nonlinear soil strength on the stability calculation of rainfall landslides is analyzed.The results show that the commonly used Fredlund linear strength model will overestimate the slope safety factor when large soil suction is.The reasonable selection of the nonlinear strength model is essential for slope stability analysis,and Vanapalli strength model is recommended.By analyzing the main control factors of fine-grained soil rainfall landslide: continuous rainfall weather is easy to induce instability and failure of fine-grained soil slope.