The Experimental Research And Comprehensive Evaluation Of Subgrade Vulnerability Under The Action Of Debris Flow

Debris flow is a common natural disaster in mountainous areas.It's a kind of solid-liquid two-phase flow containing lots of silt and rock which emerges from valley or slope.It has characteristics such as sudden outbreak,short continuance,strong destructiveness,quick damage and so on.In recent years,with the progress of the strategy of developing the west,human activities are obviously increasing as well as the Global warming and the frequent earthquakes which make the west a high incidence area of debris flow,whose natural environment and ecosystem is extremely fragile.Debris flows there are widely distributed with varied forms and frequent occurrences,and they often destroyed the bridges and culverts as well as the surgrade or widely buried the highway.The Aoyitage-Bulunkou section of Karakoram Highway(KKH)is a bottleneck because of the frequency of debris flow disasters,which has obstructed the traffic's flowing.Because of the restriction of economic condition,many sections of the road pass through the dangerous areas of debris flow by the way of subgrade,which caused the subgrade being beated and buried.The traffic was consequently disrupted sometimes,and the economic development in Sinkiang as well as people's lives was threatened by debris flow.Therefore the subgrade vulnerability under the action of debris flow disaster needs to be studied to confirm the vulnerability rank of subgrade in order to guide the route selection,the design,the repair and maintenance,and the disaster prevention and mitigation.The research of subgrade vulnerability is few,and for this reason this paper's work has important significance to guide other areas' research of subgrade vulnerability.Therefore this paper,based on the extension project of the Aoyitage-Bulunkou section of KKH,with the main debris flows and the corresponding subgrades as research subjects,the subgrade vulnerability as research purpose,the model experiment and comprehensive evaluation as research methods,focused on the following aspects:(1)According to predecessors' achievements,the concept of subgrade vulnerability was proposed.The research area' geographical environment and human activities were studied,and the forming condition of debris flow which contained terrain condition,source condition and water condition was analyzed systematically from the following aspects such as landforms,geological structure,lithology,earthquake andneotectonics,climate and hydrology,glacier,vegetation and human activities.Meanwhile the debris flows' spatial and temporal distribution features as well as their impact ways on highway were studied through field investigation.All the work provided a base for regional debris flow research.(2)Through model tests,the paper studied the debris flow' impacts on subgrade based on the undermined-stagnant debris flow gully at K1561+952~K1562+306.The changing impact force and the situation of the buried subgrade were the keystones of the research.The results consistented with the field survey results,and the results could be predicted from the model after debris flow happened.This method provided a reliable method for determining the subgrade vulnerability grade.Meanwhile the test model was used to study 6 factors through 25 experiments.The conclusion was that different factors have different impacts on subgrade vulnerability.The test research was supplemented by these experiments,and the results had instructive effect on the comprehensive evaluation of vulnerability.(3)According to the risk of debris flow,the disaster-bearing capability of subgrade and the situation of the subgrade suffering from debris flow,the vulnerability was divided into 5 grades.The assessment indexes of debris flow's destructive capacities were determined from debris flow dynamics which was quite innovative.And the subgrade's indexes were chosen from strength,deformation,and stability referring to the theory of the structure's reliability.Then the evaluating indicator system of the subgrade vulnerability was established and the indicators were divided into different grades.And that laid the foundation for comprehensive evaluation of subgrade vulnerability(4)The assessment method of Fuzzy-AHP and the coupling method of set pair analysis and triangle fuzzy ?-intervals were sutdied and applied to evaluate the vulnerability of 24 debris flow gullies and their corresponding subgrades.The results of the two assessment models were basic agreement and consistent with the findings of field investigation,which testified the reliability and accuracy of the method.