Study On Rainfall Infiltration Pattern Of Loess Slopes Based On Resistivity Detection

In recent years,extreme rainfall events have occurred frequently in loess areas,and the problem of loess landslides has become more and more serious,causing serious impacts on local production and life.The infiltration of rainfall is the most important factor leading to the instability of the loess slopes,so it is crucial to study the infiltration process of water in loess slopes and its influence on the slope stability.This paper takes a typical loess slope in Baota District,Yan’an City as the research object.Firstly,we discussed the influence of various factors on the results during the resistivity test through indoor resistivity test,and the relationship between loess resistivity and volumetric moisture content,dry density and matrix suction based on the improved resistivity measurement method was discussed;Then,the feasibility of the DC resistivity method for monitoring the infiltration of moisture in loess was verified through indoor rainfall infiltration simulation test of loess column.Finally,the TLERT(time-lapse resistivity imaging technology)monitoring data obtained from the field monitoring were inverted to obtain slope water content profiles and pore water pressure profiles,analyze the water infiltration pattern of loess slopes under different rainfall conditions,and discuss the changes of slope stability during rainfall infiltration.The changes of slope stability during rainfall infiltration are discussed.The main conclusions are as follows:(1)Through the loess resistivity test,we obtained that the test results of four-phase electrode method are more reliable than two-phase electrode method;the depth of the voltage pole probe inserted into the soil has no effect on the measurement results,explored the time effect of resistivity measurement results when DC and AC power supply,and proposed a stepwise pressurized DC signal method for the test,which improved the accuracy of indoor loess resistivity measurement.(2)Based on the improved resistivity measurement method,the volumetric water content,dry density and resistivity relationships are all negatively correlated and have a good fit with the improved Archie formula.The resistivity value of the moisture absorption curve is larger than that of the moisture removal curve for the same volumetric water content,and there is a hysteresis effect.The matrix suction of loess increases with the increase of resistivity and has a good fit with the relationship equation between matrix suction and resistivity proposed in this paper.(3)A simulation test of rainfall infiltration in loess soil column was conducted,and it was found that the monitoring of soil moisture by resistivity method is more sensitive and has higher measurement accuracy.The response time of different depths to water infiltration became longer with increasing depth.Under the condition of continuous rainfall,the relationship between wetting front and rainfall time is basically linear;under the condition of intermittent rainfall,the wetting front decreases exponentially after each rainfall and tends to be stable,and the downward movement of the wetting front slows down with the increase of the number of rainfall,and its final relative depth of decline also gradually decreases.(4)The spatial distribution and infiltration patterns of moisture on loess slopes under different rainfall conditions were obtained based on TLERT monitoring.Under the condition of short-time heavy rainfall,the rainfall has limited effect on the moisture field of loess slope,and only in the surface soil moisture content of small slope section experiences dynamic changes of increasing and then decreasing;under the condition of long-term intermittent rainfall,the moisture field of loess slope changes to a greater depth and shows hysteresis,and the shallow moisture content changes earlier and increases to a greater extent.(5)Using the data obtained from TLERT monitoring to analyze the stability of slopes during rainfall,it is found that slope stability starts to decline with rainfall,and the slope stability coefficient decreases by 0.319 within two days of short-term rainfall;the maximum decrease in slope stability coefficient during long-term intermittent rainfall decreases by0.42,which occurs after the end of the second rainfall.For shallow slip surfaces,the first few rainfalls of intermittent rainfall have a greater impact on stability.