Numerical Simulation Of Three-dimensional Flow Field And Risk Assessment At Xiaojiagou Debris Flow Of The Basin Of Jinsha Hydropower Dam Area

As one kind of geological disasters,debris flow has the characteristics of highfrequency, wide distribution and long duration,there are a lot of different scale ofdebris flows that occurs each year, causing huge loss of life and property. With therapid development of economy at mountain areas, the demand for soil resources isgrowing,due to the extreme lack of land resources, Circulation area and stacking areaformed by debris flow activity is relatively flat,which often become an importantplace for the construction of mountain villages and towns,the sudden outbreak ofdebris flow will bring serious disasters to human production and life, causing hugeloss of life and property.So the risk assessment and zoning of single debris flowdisaster has a great academic significance, at the same time, it has a far-reachingsocial significance.With the support of National Natural Science Foundation of China(NO.41330636) and MWR special funds nonprofit industry research project(NO.201001008),the geological environment,developing characteristics and flowcharacteristics of Xiaojiagou debris flow are analyzed based on satellite imageinterpretation field geological survey.A three-dimensional geological model is builtby using Surfer, Gocad and ICEM. Numerical simulation of three-dimensional flowfield of debris flow is conducted using CFX fluid simulation software, combinedwith rheological characteristics of debris flow and rheological kinetictheory.Rheological characteristics of debris flow is described by Binghamrheological model and the model parameters are determined based on the formulasfrom Fei Jun-Xiang,at the same time, k-ε turbulence modelof the single-phase flow is adopted.Based on satellite image interpretation and field geological survey, the geologicalenvironment,developing characteristics and flow characteristics of Xiaojiagoudebris flow are analyzed.A three-dimensional geological model is built by usingSurfer, Gocad and ICEM. Numerical simulation of three-dimensional flow field ofdebris flow is conducted using CFX fluid simulation software, combined withrheological characteristics of debris flow and rheological kinetic theory.Rheologicalcharacteristics of debris flow is described by Bingham rheological model and themodel parameters are determined based on the formulas from Fei Jun-Xiang,at thesame time, k-ε turbulence modelof the single-phase flow is adopted.The riskassessment the risk assessment of damaging loss is carried on based on the theresults of numerical simulations and the spatial distribution and economicdistribution of the objects affected by debris flow with the powerful data processingcapabilities of GIS. The main conclusions are as follows:The debris flow of Xiaojiagou belongs to valley debris flow, with a completepartitioning feature. Combined with field investigation and laboratory analysis,debris flow is in the prime of life, single-channel activity is strong, belong to debristype, prone level of debris flow is analyzed. On this basis,the flow rate and the totalamount of one process are caculated.The three dimensional geological model is built by the combination amongSurfer, Gocad and ICEM fistly,the spatial distribution of velocity and pressure ofthree-dimensional flow field can ba achieved under different frequencies of theoutbreak of debris flow and the effect of no dams and dams.Under differentcircumstances the movement overall trend of debris flow is basically consistent, thevelocity of debris flow is relatively faster near the forming region because of therelatively steep slope of the valley and the narrow width.With the continueddownward movement of debris flow, the velocity will gradually slow down as thevalley slope is more and more flat, and the gully width is more and more wide.Inboth cases, the flow field is similar during the first dams to the upstream, there aresignificant changes in the flow field during the first dams to the downstream.The velocity of debris flow significantly reduced at the dam,while the pressure of fluid issignificantly larger.The numerical results can be vectorized by the use of the powerful dataprocessing capabilities of GIS, combined with previous studies and thecharacteristics of the study area itself,the risk zoning of Xiaojiagou debris flow iscarried.The high risk zoning mainly distributed within the scope of dams to upstreamfor both situations,and the proportion of high risk zoning area is close, the middlerisk and low risk distribution is significantly different.According to satellite image interpretation from google and field geologicalsurvey, the objects affected by debris flow can be divided into arable land, forest,building land and transportation land,the spatial distribution and the valuedistribution of the objects will be analysized. Taking into account the differentdamaging degree of variation of the objects affected by debris flow, combined withGIS platform,the partition of the destruction loss rate is conducted based on thedistribution of the mud depth and velocity of debris flow in the study area. On thisbasis,the risk of loss damage of debris flow that breakouts500year once a time iscarried on, the total value of the loss has decreased by about40%with the effect ofdams,which plays a important role in the disaster prevention and reduction.