Study On Initiation Mechanism Of Debris Flow Slope Source In Meizoseismal Area After Earthquake

"5.12" wenchuan Ms8.0 earthquake magnitude earthquake mountain structure damage,caused a large number of coseismic surface rupture,results in a large number of shock dispersion slope distribution of earthquake source,lead to early mountain slope surface weathered eluvial slope vegetation degradation,crack development,under the effect of rainfall,slope erosion gully erosion,sheet erosion,shallow slumping slide,slope gustiness flow on different degree way to participate in the activities of slope debris flow,soil and water loss into the channel by channel source supply.According to the field investigation and related exploration data,the total amount of slope provenance and dynamic reserves account for a large proportion of the total amount of provenance in the basin,which has become an important source of debris flow after the earthquake.The starting mechanism of material source and the calculation of dynamic reserves have important guiding significance to the design of debris flow control engineering.Starting mechanism based on the slope surface source and dynamic calculation of reserves as the research object,the contents related to designing orthogonal indoor model test,analysis of the different combination conditions of rainfall,slope,herbaceous vegetation density downhill starting mode,surface source rain starting sensitivity factors reveal slope source sorting,root system in soil mechanics model is established and analyzed the instability of slope surface source poor damage mechanics,and compared the method of engineering experience and RUSLE model estimate of the slope surface source dynamic reserves results;On the basis of the indoor model test,the numerical simulation analysis is carried out to reveal the influence of the vegetation on the seepage field of the slope.The main conclusions are as follows:(1)According to the results of sensitivity analysis on the starting of the slope provenance rainfall,the primary and secondary order of the influencing factors on the starting of the slope provenance instability is: slope > rainfall intensity > vegetation cover density.And "steep slope + heavy rainfall + minimum vegetation coverage"(slope 45°,rain intensity 50mm/h,vegetation density 20 plants /?)is the best for the slope source instability start.(2)From the phenomenon of indoor model test,slope is the main factor to control and influence the starting process of slope material source,and the instability failure process of slope material source can be divided into two categories: erosion type and overall instability type.The failure process of erosion type can be divided into the following stages: initial infiltration ? local saturation,surface erosion ? slope settlement,local creep ? local instability,slump ? local slope debris flow.The instability failure process of overall instability type can be divided into the following stages: initial infiltration ? overall instability ? creep,slump ? traceable erosion ? large area explosion.(3)At present,the method of calculating the dynamic reserves of slope(erosion thickness by erosion area)is extensive.determine the extensiveness of an there,under the condition of steep slope sediment source,according to the existing engineering experience to calculate dynamic reserves and the slope of source RUSLE method calculated results was 222%,and the biggest difference in control in the basin rainfall data,vegetation coverage,source rock mass parameters under the condition of such information,can consider various influencing factors of slope erosion source,using RUSLE model calculating unit area of years of erosion,slope surface source and conversion for engineering the period of validity of a more comprehensive and accurate dynamic reserves.(4)It can be seen from the simulation results of the seepage field that under the same rainfall duration(1200s),only the shallow surface of the root soil is in the saturated state,while the exposed slope is saturated as a whole.In addition,in the same group of simulation,the reduction rate of matric suction in the root soil lags behind that of the lower soil.(5)It can be seen from the simulation results of the displacement field that slope is the key factor to control the deformation of the material source on the slope under the condition of rainfall,and the creep deformation of the material source on the downhill slope under the condition of 45° slope is more significant than that of the 30° slope.Under the condition of 30° slope,there was no significant difference in the displacement field between the slope with roots and the exposed slope.Moreover,under the condition of this slope,the creep deformation of the slope body was reduced by 12.5% due to the reinforcing effect of roots,which was lower than the inhibiting effect of the reinforcing effect of roots on the slope surface at 45° under the same condition(17%).