Study On The Characteristics And Outthrust Of Debris Flow In Steep Gully In Earthquake Region

Wenchuan geological environment after the earthquake becomes more fragile,collapse,landslide,debris flow and other geological disasters.Debris flow is one of the major hidden dangers threatening the lives and property of residents.The characteristics of debris flow after earthquake are as follows: the number increases sharply,the frequency increases,the scale increases,the critical rainfall decreases,and most of them are viscous debris flow.Among the numerous debris flow disasters,there is a kind of debris flow which is particularly typical and special.This kind of debris flow gully has a low degree of development before the earthquake and rarely occurs debris flow.Wenchuan earthquake provides sufficient material source for it,which leads to a sharp increase in the activity of this kind of debris flow.This kind of debris flow gully basin has a small area and a very steep gully with a vertical ratio of more than 300‰.Its topographic features are similar to those of gully debris flow in general and have the characteristics of slope debris flow at the same time.On this basis,through to the wenchuan strong earthquake debris flow valley topography characteristics of statistical analysis and the analysis of characteristics of debris flow,initially defined the basin area longitudinal slope > < 5 km2,channel by an average of 30%,watershed integrity coefficient of < 0.4,and the debris flow on both sides of the slope of 35 ° or debris flow valleys type to the steep channel debris flow.Although the basin area of this kind of debris flow is small,it is of great significance to study its dynamic characteristics and outthrust amount once the disaster damage is much greater than that of the same scale of general gully and gully debris flow.In this paper,the dynamic characteristics and outbursts of such debris flows are studied by mechanical analysis,regression statistics and numerical simulation,and the following conclusions are obtained:1.Taking the drainage area(A),relative height difference(H),longitudinal slope of gully(J),longitudinal length of gully(L)and area of landslide accumulation in the basin(AL)of 27 steep gully debris flows in wenchuan earthquake area as the influencing factors of outrush volume,the outrush volume prediction model of such debris flows is explored.Through correlation analysis,correlation and rushed out of the amount of deposit by order for the collapse area,the basin area,relative elevation difference,the longitudinal slope,vertical channel length,channel first three correlation coefficient is big,after the two correlation coefficient is small,therefore,choose the first three as rushed out of the fitting parameters of established V = 14.3571 H0.2797 A0.2367 AL0.2731 rushed out of the prediction model.Finally,the accuracy of the fitting formula is analyzed accurately.Through verification and error analysis,it can be seen that this model has certain applicability in predicting the outrush measurement of debris flow in steep gully in wenchuan earthquake area.2.Through the mechanical analysis and data statistics,the thorough analysis of the steep steep channel characteristics of debris flow under the condition of natural movement,found in steep channel slope debris flow channel,the channel deposits starting similar to slope debris flow,under the condition of rainfall debris flow deposits formed in the pore water pressure and osmotic pressure,the debris flow deposits sustained strong shear strength reduction,the final channel deposits along the potential sliding surface of shear failure,river basin upstream rapid confluence form flash floods,mountain torrents of high dynamic water pressure similar to "fire fighting" effect scour channel debris flow area,mountain flood carrying channel source development for debris flow.SPSS software was used to conduct regression statistics on erosion characteristics,flow characteristics and flow velocity characteristics of debris flow gully in three typical steep gully,namely,wayao gully,shaofangou gully and xiaogangjian gully.The velocity of debris flow is related to the longitudinal gradient of gully.The flow rate of debris flow is related to the vertical ratio of gully,cross-sectional area and depth of debris flow.3.Considering the mudslide 3-d numerical simulation and the 2-d numerical model,the difference between a provided respectively using three-dimensional fluid dynamics software ANSYS CFX and two-dimensional flow field simulation software FLO-2 d of gully and tile kiln burning room respectively under three kinds of rainfall frequency(P = 2%,P = 10%,P = 20%)mudslides rushed out of the process is simulated,the velocity distribution,flow field distribution and rushed out of the scope,rushed out of the quantity,rushed out of the distance,pile up fan form data,such as to get results and the actual situation of "8.13","7.10" landslide,analyzes its error.Simulation results show that the outfall distance,outfall amount and outfall range are positively correlated with rainfall frequency.The accuracy of numerical simulation software in predicting outfall amount is greater than that of regression statistical model.