| Heavy rain are frequent in the southeastern coastal areas of China,and the infiltration of rainwater under downpour is an important cause of landslides in hilly mountains.In this dissertation,the response characteristics of slope hydrological parameters to rainfall were analyzed by establishing a prototype field test site for landslides located in Yao Mountain,Xiping downtown,Anxi county.The automatic monitoring system of this test site can monitor six parameters,including rainfall,water content,pore water pressure,groundwater level,deep soil displacement,and surface fractures.Combining with the actual situation of the study area,a rainfall infiltration model that integrates the inhomogeneity of the initial water content distribution of the soil and the slope environment was established.In theory,a more in-depth study on the migration law of rainwater infiltration and wetting front and the early warning of landslides,and the model was compared and analyzed by using field test data and classical model calculation results.The results of this study can provide a basis for rainfall-based landslide warning.The main contents and results of this study are as follows:(1)According to the rainfall infiltration wetting front migration distribution law obtained from the Xiping Yaoshan landslide test site in Anxi,the soil profile can be divided into transient saturated zone,saturated conduction zone,and unsaturated zone from top to bottom.At the initial stage of rainfall infiltration,the migration rate of wetting front is fast,and the volumetric water content increases at different depths at a steeper slope.As time goes by,the slope gradually slows down.When the accumulated rainfall reaches 44.4mm or more,the water content profile of the soil body changes from "Z" to reverse "S".As the rainfall intensity decreases,the process of rainwater infiltration changes from accumulated water infiltration to non-accumulated water.In the later stage of infiltration,the infiltration rate of rainwater gradually decreases,and the growth rate of volumetric water content at different depths tends to a constant,and a stable infiltration stage was reached.(2)Considering the inhomogeneity of the initial water content distribution and the suitability of the model to the slope environment,the improved Green-Ampt model was used to calculate the variation of the wetting front depth with time.The calculation results are consistent with the field monitoring test results.The measured wetting front on site and the model solution error were analyzed the results show that: The calculation accuracy of the GA model will be further improved by considering the variation characteristics of the water content of the unsaturated conduction zone in the slope environment and the unevenness of the initial water content distribution.The average rainfall response time of water content at different depths under 23 rainfall events in the past year was calculated,and the relationship between the wetting front and time applicable to the study area was obtained.(3)For the study area,the stability coefficient with the wetting front as the slip surface is smaller than the stability coefficient with the interface between the saturation zone and the elliptical transition zone as the slip surface.With the advancing of the wetting front,the increase in the weight of the saturated soil in the soil mass causes an increase in the sliding force of the slope.At the same time,the decrease in the suction of the soil matrix and the increase in pore water pressure also cause the sliding resistance of the slope to decrease,and finally reduce the stability coefficient.Compared with the infiltration condition of stagnant water,it takes longer to reach the same depth of infiltration under the condition of non-accumulating water infiltration.This shows that the hysteresis effect of rainfall-type landslides is more obvious for the characteristics of low rainfall intensity and long duration in spring.(4)According to the change characteristics of displacement acceleration,the rainfall-type landslide deformation characteristics in the study area are divided into three stages: initial deformation stage,acceleration deformation stage,and deceleration deformation stage.When the landslide enters the accelerated deformation stage,the displacement acceleration changes from negative to a positive,and the "sudden jump" phenomenon of the displacement acceleration can provide an early warning signal for the landslide.According to the slope stability coefficient,the landslide warning level in the study area is divided into four levels: Ⅰ-safety,Ⅱ-low risk,Ⅲ-medium risk,Ⅳ-high risk.The landslide warning thresholds of different warning levels are derived under comprehensive consideration of displacement acceleration,average groundwater level,average pore water pressure,rainfall and other parameters. |
