Characteristics And Risks Assessment Of The Debris Flow In The Highway G318 From Linzhi To Lhasa

The G318 Linzhi-Lhasa section highway starts from Linzhi Town in the east and ends at Chengguan District in Lhasa in the west,with a total length of 420 km.It is an important channel for Sichuan-Tibet economic exchanges and national defense material transportation.The terrain along the highway is undulating,the rock and soil mass are broken,and the debris flow is strongly developed,which seriously affects the normal operation of the highway.The debris flow along the G318 Linzhi-Lhasa highway were token as the research object,and a debris flow disaster database was established by means of historical data collection,remote sensing interpretation and field investigation.Based on the coupling relationship of the control factors,the debris flow risk evaluation index was further analyzed,a risk evaluation model was constructed,and the debris flow risk evaluation and zoning were carried out based on the GIS space platform.The main research contents and achievements of the paper are as follows:(1)Collect natural conditions and geological environment data in the study area,use remote sensing images to interpret debris flows in the study area,combine field investigations,build a debris flow disaster database,and draw relevant maps based on debris flow disaster-pregnancy environment and distribution law control factors for further analysis.The law of debris flow distribution and risk assessment provide numerical support.(2)Based on the debris flow hazard database,qualitatively classify debris flow trenches and analyze the development characteristics of debris flow.The debris flow in the study area is mainly rainstorm type small-scale rare low-frequency debris flow,and 62.9% of the debris flow trenches are in a vigorous development period.The formation conditions of the debris flow were analyzed by remote sensing interpretation and field investigation: the terrain conditions of the debris flow were analyzed based on factors such as slope,slope aspect,and terrain relief.Outburst flood;based on field investigations,it can be seen that the main sources of debris flow are landslides,slope erosion,channel accumulation,moraine and human engineering waste slag and waste.The motion characteristics of debris flow and the characteristics of typical debris flow ditch motion parameters(bulk density,velocity,flow rate and peak debris flow rate,etc.)of debris flow were calculated and analyzed by mathematical model,which provided theoretical basis and data support for the construction of debris flow prevention and control projects.(3)Based on the debris flow disaster database,the coupling relationship between the distribution law of debris flow and the controlling factors was analyzed by mathematical statistics.The distribution law of debris flow under the conditions of topography,meteorology,hydrology and geological structure: the average disaster density in the east of Mila Mountain is 0.490km/bar,and the average disaster density in the west of Mila Mountain is 0.275km/bar;regional debris flow distribution density in narrow valleys is greater than The Kuangu section and the Niyang River Basin(with high rainfall)are larger than those in the Lhasa River Basin(with low rainfall);about 70.7% of the debris flow trenches are faulted,and the development of debris flow in the faulted area is relatively strong.Coupling analysis of distribution law controlling factors shows that slope and average gradient have a close positive correlation,rainfall and fault density have a very close positive correlation,and average gradient has a close negative correlation with watershed area.(4)Based on the analysis of the development characteristics and distribution law of debris flow,the paper adopts the watershed area,terrain slope,ditch-bed gradient,relative height difference vegetation coverage(NDVI),fault density,stratigraphic lithology,seismic peak acceleration and annual average rainfall.9 evaluation indicators are used to evaluate the hazard of debris flow based on the HRU unit.The results showed that the high-hazard area in the assessment area accounted for the largest proportion,accounting for 37.62%,followed by the medium-hazard area,the low-hazard area,the low-hazard area and the high-hazard area,and the high-hazard area was the smallest,accounting for about 4.26%.(5)The vulnerability of road engineering in the debris flow basin is jointly controlled by exposure,engineering structure properties and debris flow activity characteristics.After analysis,8 indicators including the distance from the road to the mouth of the debris flow ditch,the angle between the road and the debris flow ditch,the way of the road,the maintenance intensity,the prevention and control works,the form of debris flow hazard,the scale of the debris flow and the frequency of debris flow are used to evaluate the vulnerability of the highway.The results show that the area of the higher vulnerability area in the evaluation area accounts for the largest proportion,accounting for 41.43%,followed by the low vulnerability area,the high vulnerability area,the medium vulnerability area and the lower vulnerability area,and the lower vulnerability area is the smallest,about approx.4.26%.Based on the debris flow risk assessment and engineering vulnerability assessment results,risk assessment and zoning of the study area are carried out through the Arc Gis platform.The results showed that the higher risk area in the assessment area accounted for the largest area,accounting for 24.62%,followed by the low risk area,high risk area,and medium risk area,and the lower risk area was the smallest,accounting for about 13.33%.