Debris Flow Susceptibility Assessment Of Karakoram Highway And Experiment Of Initiation Mechanism

Karakoram Highway is located in the hinterland of west Kunlun Mountains.Because of its complex terrain conditions,geological conditions and harsh climate conditions,this highway has been under the influence of debris flow since it was built to traffic.However there are few researches on debris flow along Karakoram Highway in China,which makes it lack of effective measures to prevent and control debris flow disasters.Since “The Belt and Road Initiative” strategy was put forward by central government,the economic and strategic status of Karakoram Highway has been greatly improved.In order to get rid of the influence of debris flow disasters on the reconstruction highway,the degree of debris flow susceptibility along the highway was evaluated and a laboratory test on the initial characteristic of debris flow was conducted by our research group based on the project “Study on the cause of formation,distribution and engineering treatment of debris flow of Karakoram Highway”.Thus scientific guidance for route selection and disaster prevention and mitigation could be provided.K1562 debris flow gully was chosen as the prototype of the laboratory test to explore the initial characteristic of debris flow and analyze the effects of different experimental conditions on debris flow susceptibility.Then according to the data collected in-site and relevant background information of study area,the debris flow disasters background was deeply analyzed,then several relevant indexes were chosen to establish the index system of debris flow susceptibility evaluation,finally two kinds of methods which were the normal cloud model and the connectional expectation were applied to evaluate the degree of debris flow susceptibility along Karakoram Highway.The following conclusions could be drawn through the research:(1)Based on terrain,geology and hydrology of debris flow,the background information of debris flow formation in the study area was described in detail so that the causes of frequent debris flow disaster were revealed.Finally,several laws of the temporal and spatial distribution of debris flow disasters in the study area were summarized.(2)In order to explore the influence of debris flow susceptibility index system on debris flow initial and susceptibility,K1562 debris flow was chosen as the test prototype,then the quasi debris flow in the original area was gathered as the test soil,after that the similarity ratio was determined as 1:100,finally 20 laboratory tests were carried out in 6 groups.In this paper,the critical water content was put forward as the measure standard of debris flow susceptibility,through laboratory test the variation laws between gully slope,soil grain composition,runoff velocity,fracture morphology,soil thickness,soil moisture and the critical water content,peak pore water pressure,time to peak pore water pressure were obtained.Then the regression analysis was applied to fit the function of the laws so that the corresponding variation trend could be analyzed.According to the critical water content,the influence of different test conditions on debris flow susceptibility could be induced and the results showed that all the selected factors had an impact on debris flow susceptibility and the influence of gully slope,soil grain composition,runoff velocity and soil moisture on debris flow susceptibility was greater than that of fracture morphology and soil thickness.(3)Based on the testing data,the critical water content of prototypical K1562 debris flow could be calculated by similarity theory.Compared with the flood-peak discharge obtained by theoretical calculation under the storm rainfall of 15mm/h,the results showed that debris flow disaster was more likely to break out in the prototypical debris flow gully under this storm rainfall.So in this paper the critical water of prototypical K1562 debris flow was proposed as quantitative theoretical basis of debris flow disaster forecast.(4)According to the results of laboratory test and code for investigation of debris flow,combined with the actual situation of Karakoram Highway,soil erosion,sediment supply length ratio,debris flow accumulation,gully longitudinal slope,regional tectonic,vegetation coverage ratio,lithology effect,loose materials reserves,bank slope,trench cross-section,the average thickness of loose materials,drainage area,relative height,the degree of blocking were chosen as the susceptibility evaluation indexes.In this paper,the degrees of debris flow susceptibility were divided into four grades and the weight of each evaluation index was determined so that the index system of debris flow susceptibility was established.(5)The normal cloud model and connectional expectation model were respectively established to apply to evaluate the susceptibility of 32 debris flow in the study area.Compared with the calculation results and the survey results,it showed that the debris flow in the study area was with a high susceptibility degree and occurred frequently,which extremely high susceptibility debris flow accounted for 53%,moderate susceptibility debris flow accounted for 44% and mild susceptibility debris flow accounted for 3%.As far as the two models were concerned,the evaluation results of the normal cloud model were not only more accurate than that of the connectional expectation model but also more conservative and safer.Generally,it was shown that the normal cloud model was more suitable for debris flow susceptibility evaluation than the connectional expectation model.This paper has greatly enriched the research of debris flow along Karakoram Highway in two aspects: the evaluation of debris flow susceptibility and the initial characteristic of debris flow,providing guiding advices for route selection and disaster prevention and having important reference significance to following debris flow research in this area.