| When rainfall acts on a slope,usually the rainwater movement includes both the infiltration of the slope and the generation of runoff on the slope.Previous studies have shown that there is a certain difference in infiltration rate between neglecting runoff and considering runoff effect.However,taking runoff effect into consideration in existing studies is scarce.Studies covering the interaction between runoff and the infiltration of slope are mostly found in the field of soil-water conservation,which rarely combined with the landslide stability analysis.In addition,the actual situation could not be reflected well in model tests,and the research object is often focused on a single infiltration-runoff feature or stress-displacement response characteristic,the correlation analysis on different physical quantities is lacking.Besides,related engineering applications considering the slope runoff effect stability for landslides The of sexual influence are rare.Therefore,on this account,supported by the Venture&Innovation Support Program for Chongqing Overseas Returnees?CX2017125?,taking the Caijiaba landslide in Yunyang County of Chongqing as a case study,this paper focus on the runoff problem during rainfall infiltration process by means of theoretical analysis,numerical simulation,indoor large-scale model test,and indoor unsaturated soil transient hydraulic characteristics circulation test.Combined with kinematic wave theory,subsurface flow theory,unsaturated soil mechanics,etc.,runoff characteristics,infiltration characteristics,coupled effect of rainfall runoff and subsurface flow seepage,characteristics of stress field and seepage field,as well as the coupling model of runoff-subsurface flow application in landslide case study,have been systematically studied.The main research results obtained are as follows:?1?Based on multi-source data,i.e.,satellite remote sensing image,high-definition UAV photography,historical record data,on-site survey data,etc.,perspectives of multiple scales were achieved.The scope,characteristics,and occurrence geological environment of the Caijiaba landslide were defined.Afterwards,based on drilling,combining trenching,well exploration and geophysical exploration,indoor and field experiments were carried out,landslide area formation,sliding zone and physical and mechanical properties were ascertained.The field survey showed that the Caijiaba landslide is an large multi-stage bedding landslide.The topography of the landslide is relatively simple,and the favorable terrain conditions are the basis for the generation and development of runoff.At present,there are soil sliding and rock sliding,and soil sliding and shallow-middle rock sliding are more prominent.?2?Taking the Caijiaba landslide as the prototype,through an artificial rainfall system that can accurately control rainfall parameters,a self-designed runoff-infiltration measurement device,a digital speckle correlation device,and related stress measurement sensors,an indoor model test on sandy clay slope was conducted.During the rainfall process,surface runoff,water content of slope,pore water pressure,earth pressure,matrix suction,runoff and sediment generation,and displacement of the slope were analyzed and discussed.The interaction between the infiltration-runoff process and different physical quantities was mainly discussed.The results of model tests show that there is a certain correlation between outflow of runoff and infiltration.When runoff and infiltration reach a certain stable stage,the effect of increasing rainfall intensity on the infiltration rate is very weak.The seepage erosion has a significant correlation with surface erosion.When the slope reaches a certain stable state,the increase of rainfall intensity has no obvious effect on the aggravation of the seepage erosion of the slope.The trend of the pore water pressure and the infiltration-runoff phenomenon are related.When the infiltration rate of the slope tends to be stable,the pore water pressure also reaches a stable state,and the corresponding variations of matrix suction also have a certain relationship with the surface runoff.The earth pressure gauge at different positions of the slope has different responses in the initial stage of rainfall,and the earth pressures at different locations have different responses.When the rainfall intensity is increased,the slope runoff increases accordingly.Many gullies and fissures were appeared because of the continuously surface runoff scouring,under the coupled effect of infiltration-runoff,the response of horizontal displacement is more obvious,and a more obvious displacement change near the toe of the slope was observed.?3?Using the one-dimensional surface runoff kinematic wave equation and the two-dimensional subsurface flow Richards equation,based on the TP Flow module based on the software Flac 2D and the self-produced Fish program,a new method for the coupling analysis of surface runoff-subsurface flow was proposed.The infiltration-runoff characteristics of the slope under rainfall were discussed.The stability of the landslide under rainfall is studied in combination with the Bishop effective stress theory and limit equilibrium theory of unsaturated soils.Then,the landslide stability based on the coupled model of surface runoff-subsurface flow was studied.Finally,the theory application to a case study was conducted,from the case it is revealed that the surface runoff has a non-negligible impact on the infiltration of the slope,and the analysis of the coupled model of surface runoff-subsurface flow has a relatively more reasonable assessment of the seepage field of the slope.Under the joint action of the slope runoff,rainfall infiltration,and wetting front,there is a more obvious mechanical response near the toe of the slope compared to the upper part of the slope.The horizontal displacement at the slope surface is the largest,with the depth increases,the horizontal displacement decreases gradually.?4?Based on Transient Release and Imbibition Method device,the hydraulic properties of unsaturated soils were obtained from the soil samples taken from the Caijiaba landslide site.The test path was numerically simulated by Richards equation,and the van Genuchten soil-water characteristic curve model and Mualem hydraulic conductivity function model were used to invert the hydraulic parameters related to the soil samples.The test data is fitted by HYDRUS-1D software,then,the soil water characteristic curve,hydraulic conductivity function curve,and hydraulic characteristic parameters of the two soil samples were obtained.It could provide a basis for the selection of relevant calculation parameters when the coupled runoff-infiltration model is applied to landslide engineering case studies.?5?According to the actual rainfall data of the landslide area,the physical and mechanical parameters of the rock and soil obtained from the landslide site,and the hydraulic characteristics parameters obtained from the TRIM test,typical geological section of Caijiaba landslide was selected and analyzed based on the coupled runoff-infiltration model by means of numerical simulation.The numerical results show that the runoff has a significant influence on the pore water pressure and the distribution of slope saturation.The wetting front reaches a deeper depth when considering runoff effect on the slope infiltration.The runoff phenomenon appears earlier under greater intensity of the rainfall,while the runoff phenomenon occurs later under the smaller rainfall intensity,therefore more rainwater infiltration into the slope.Considering the runoff effect,the slope displacement is relatively larger,and the horizontal displacement of the slope has a more obvious response under the smaller intensity of rainfall.Comparing with the measured displacement of chosen monitoring points at the Caijiaba landslide,it could be seen that the monitoring results are in good agreement with the numerical calculation results when considering the runoff effect.?6?The case study simulation results also show factor of safety of the landslide considering runoff effect is different from the factor ofsafety when runoff is not taken into consideration,and the factor of safety is in good agreement with the actual situation when considering the runoff effect.The factor of safety is generally small at the toe,the shoulders and the bottom of the soil near the bedrock of the slope,and some local slidings may occur.Under smaller rainfall intensity,there is a smaller safety factor than larger rainfall intensity,and the minimum safety factor appears at the toe of the slope.In addition,the safety factor under the smaller rainfall intensity is basically 1 at the contact between the soil layer and the rock layer,indicating that it is in the critical instability state.The comparison with the field survey of the slide zone at the bottom of the landslide accumulation layer?nearly the interface between rock and soil?verified the rationality of the numerical simulation. |
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