Study On Instability Mechanism And Stability Evaluation Of Rainfall-induced Residual Layer Slope

Ningxiang City,Hunan Province is located in a subtropical monsoon climate zone with abundant rainfall.Rainfall-induced landslides in the residual layer cause huge losses to local residents' lives and property every year.In view of this,this paper relies on the Lijia slope of Heli Formation in Ningxiang City to study the instability characteristics and early warning methods of rainfall-induced residual layer landslides.First of all,this paper refers to the on-site drilling data and conducts on-site investigation to find out the engineering geological environment such as topography,stratum lithology,meteorology and hydrology in the area where the Lijia slope is located,and combined with the electric method instrument to investigate undesirable geological disasters such as karst caves.On this basis,select the research profile and deploy Beidou GNSS online monitoring equipment to monitor the slope in real time.Set June 10 to June 23,2019 as the first rain phase,and July 4 to July 14,2019 as the second rain phase.And through the analysis of the monitoring data,the slope is initially stable.Secondly,based on the VG model,rainfall infiltration model and mechanism,the characteristics and process of rainfall infiltration on the Lijia slope were analyzed,and the parameters of the VG model and the unsaturated permeability coefficient curve were analyzed by combining with the indoor tests such as pressure plate test and permeability coefficient test.Finally,combined with the rain gauge data,the model boundary conditions are applied and the numerical simulation analysis is carried out.Based on the simulation results,the changes of the pore water pressure field with the duration of rainfall,the relationship between the slope's overall stability and rainfall intensity,the relationship between the surface displacement and the stability coefficient,and Research on the establishment of early warning model in four aspects.The main conclusions are as follows:(1)As the rainfall progresses,it is first expressed to the saturated state,and then the diffusion speed of the transient saturation area at the foot of the slope is accelerated,and eventually diffuses from the foot of the slope to the top of the slope;the second rain stage is easier to slope than the first rain stage Reached saturation;(2)The horizontal displacement of the surface has obvious convergence lag relative to the change of rainfall data and has a gradual accumulation effect;the deformation trend of the slope top,middle and foot of the slope is the same at the same time;(3)There is a hysteresis in the change of the stability coefficient;after the rain stops,the stability coefficient will continue to decline for a period of time;there is a different linear relationship between the two rainfall stages,and the magnitude of the horizontal displacement changes with the stability coefficient: first rain stage> second Rain phase;(4)Establish a yellow,orange,and red three-level slope stability early warning evaluation method based on horizontal displacement data-a threshold setting method for each rainfall stage.