Study On The Influence Of Prophase Fainfall To The Initation Model Of Debris Flow In Meizoseismal Area

After the the "512" wenchuan earthquake， the phenomenon such as loose andbroken rock has formed thousands of landslide，collapse in Qingping township.Strongearthquake force induced by a large number of geological disasters. The bulkdistribution on the gully Qing Pingxiang meizoseismal area，provided rich material forthe secondary geological disasters. on August13，2010， qingping township startedto continuous heavy rain， caused the11debris flow disasters near the qingping townat the same time， which caused significant casualties and property lossesThis paper surveys and analyzes three aspects of the "5.12" earthquakemeizoseismal area qingping township of debris flow gully as topography， provenance，and catchment of rainfall characteristics. Find out the large debris flow channelmorphology， provenance and developmental characteristics of the scale in qingpingtownship represented by Wenjia gully. By installing rainfall testing meter of each gullyin Qingping township to analysis the rainfall spatial distribution characteristics ofrainfall intensity， rainfall time of qingping township especially in Wenjia gully. Byanalyzing sample of different position in wenjia gully， we get the average grain sizedistribution， clay content， compaction degree， initial moisture content of the loosedeposit.On the analysis based on the field investigation data， in order to furtherunderstand the influence of the change of initial moisture content and matrix suction inthe loose deposit caused by the process of rainfall infiltration and evaporation for thestart pattern of the loose deposit forming debris flow，we conducted three types ofexperiment:1) the tests of soil water characteristic curve of the pressure plate and box，2) large soil column rainfall infiltration test3) flume test of start model of debris flow1) through the tests of soil water characteristic curve of the pressure plate and box， We get the soil water characteristic curve of different particle size of loose deposit. theresult showed that the the suction is reduced gradually with the continuousimprovement of the moisture conten of loose deposit. When the moisture content is inthe range from5%to15%， the corresponding suction increase slow with the ofmoisture content decrease， When the moisture content is in the range from0%to5%，the corresponding suction increase very fast with the loss of the moisture content.，Themore clay content in loose deposit， the greater the suction is. when the moisturecontent is smaller than8%. With water content declining， the suction gap is moreobvious under the different clay content. The moisture absorption curve are lower thanthe dehumidifying curve. that is to say， the value of moisture absorption curve ofsuction is slightly less than the value of dehumidifying curve under the same moisturecontent.2) by large soil column rainfall infiltration test， we get the change of matrixsuction and initial moisture content with rainfall duraiton at different soil location，under constant prophase rainfall intensity. the results showed that the infiltration line isnot a horizontal line， and the Angle of the infiltration line is non-uniform. as therainfall infiltrating， the angle of the infiltration line is changed with the increase of thedepth of infiltration.the direction of the rainfall infiltration line has a certainrandomness. Fitting the equation of the relationship among prophase effective rainfall，the rainfall intensity and rainfall time. We obtained the change rule of the moisturecontent of infiltration in loose deposit. infiltration Started from top to bottom. The topof the loose deposit quickly saturated. As infiltration further， Central loose depositbegan to saturation. when the rain infiltration to the underside， the moisture content ofthe loose deposit distribution basic remain unchanged. Based on the analysis the data ofsuction and moisture content， we fit a of nonlinear equation of the relationship amongthe initial moisture content，the rainfall time and the depth of loose deposit. After therain，we studied and analysis the evaporation process also. the results show that degreeof moisture evaporation is decreases with the increase of depth， and evaporation ismost severe in the first12hours. at last，we are fitting out the by fitting a formula ofrelationship among the moisture content，the evaporation time and the depth of soilcolumn.3) by flume tests of start model of debris flow， it is concluded that there are threekinds of startup mode under different initial moisture content. When the moisturecontent of3%，4%，5%， are the failure modes for whole instability and sliding，all backup water infiltrated in the slope， after reach a certain degree of saturation， the slope whole slided. When the moisture content is12%and15%， slope failure mode isresistance effect mode. Most of the backup water seeping into the slope than the slopesurface runoff， then the erosion gully formation， the entire process repeatedresistance effect. When the moisture content is between6%and11%， first surfaceerosion， then overall buckling， finally into the resistance effect of collapse failuremode.Finally， on the basis of the study， we presented three different kinds decisionmethod of debris flow boot mode in meizoseismal area based on the differentparameters (prophase fainfall monitoring data， field monitoring data of the moisturecontent， field monitoring data of suction).