| The landslide-generated impulse wave is a secondary disaster formed after the landslide enters the water,and its damage is often far beyond the damage of landslide itself.Since the impoundment of the Three Gorges Reservoir Area,it has been affected by inundation,submerging as well as the large fluctuation of water level,which weakens the stability of potential landslides,increases the probability of the resurrection of ancient landslides.As a result,the landslide-generated impulse wave disasters occur frequently and seriously threaten the shipping safety in the reservoir area,furthermore causes great losses to social development and national economy.Therefore,it is very necessary to carry out the study on landslide-generated impulse wave disasters and its risk assessment in the Three Gorges Reservoir Area.In this paper,the hazard of landslide-generated impulse wave and the vulnerability of disaster bearing body were studied by physical model tests,and the risk of individual landslide-generated impulse wave disaster is evaluated.On this basis,the index system of regional landslide-generated impulse wave disaster risk evaluation was constructed,and the regional comprehensive evaluation of landslide-generated impulse wave disaster risk in the Three Gorges Reservoir area was conducted based on cloud theory.The main work and achievements were as follows:(1)Physical model tests of landslide-generated impulse wave characteristics were conducted.A physical model was designed to study the characteristics of landslide-generated impulse wave based on the Jiangnan Tuokou wharf in Wanzhou district of the Three Gorges Reservoir Area.According to the test results,splashing waves and impulse waves followed after the landslide enterd into the water.The splashing waves had greater disaster intensity but with a smaller impact range,mainly located in the impact zone of the landslide entering the water.The wave height of the impulse waves was relatively smaller,but the disaster area was larger,covering the impact area,near field area and far field area.It is further found that landslide-generated impulse wave was a nonlinear wave,its peak and trough were asymmetrical,and the relative wave height and relative wave amplitude had an exponential relationship.In most cases,the first wave was higher than the second one.From the perspective of disaster-causing factors,the test results provide a basis for the construction of landslide-generated impulse disaster risk evaluation index system.(2)Experimental study on the dynamic process of landslide-generated impulse wave disaster was carried out.In this paper,the disaster situation of the main disaster-bearing bodies such as navigating ships,mooring ships,anchoring ships and wharves exposed to the landslide-generated impulse wave disaster were studied.The results show that under the action of landslide-generated impulse wave disaster,the navigating ship moved in the forms of rolling,pitching,swaying and swaying and so on.When the impulse waves exceeded some certain threshold values,the navigating ship inclined too much and the container would fall into the water.The mooring ship impacted repeatedly the wharf pile,and the force acting on the cable was greater than the damage load of the cable,and the cable had the risk of breaking.The higher the wave height was,the greater the mooring force was.In the restriction of impulse wave impact and anchor chain,the mooring ship moved reciprocately in the range of maximum displacement on both sides of the ship.When the wave height of the landslide-generated impulse wave was larger,the anchor chain would bear more tension than the ultimate bearing capacity,and the anchoring ships were in the risk of dragging.Based on the experimental data,the relationship between anchor chain tension and wave height,wave period was refined and revealed.The landslide-generated impulse wave impacted on the pile in the form of dynamic pressure,which was constant below the water surface along the vertical direction and its magnitude was correlated with the wave amplitude as well as wave celerity.Based on the interaction of inertia and velocity components,the empirical formulas for maximum positive wave pressure and minimum negative wave pressure were established.From the perspective of disaster bearing body,the test results provide a reference for the selection of landslide-generated impulse wave disaster risk evaluation indexes.(3)The risk evaluation of single landslide-generated impulse wave was studied.Firstly,the hazard of single landslide-generated impulse wave disaster was explored,the extent of landslide-generated impulse wave disaster was demarcated according to the magnitude of wave height,and could be further divided into different hazardous zones.Then the theoretical calculation formula of landslide-generated impulse wave duration was deduced.Secondly,the exposure,fragility and vulnerability of the disaster bearing body exposed to the landslide-generated impulse wave were analyzed,on this basis,the calculation methods of the exposure of population and navigating ships were established and the vulnerability classification standards of various disaster bearing bodies and the expression of the vulnerability were given.Finally,taking Sifangbei landslide as an example,the landslide-generated impulse wave disaster risk under different water levels in the Three Gorges Reservoir Area was evaluated.As a result,the impact range of landslide-generated impulse wave was scoped,and the distribution of the disaster bearing bodies was determined,the result of landslide-generated impulse wave disaster risk grading was obtained.(4)Regional landslide-generated impulse wave disaster risk evaluation was studied.The risk system of landslide-generated impulse wave disaster was analyzed from three perspectives: the hazard of disaster-causing factors,the vulnerability of disaster-bearing bodies and the effectiveness of disaster prevention and reduction.After three stages of index primary selection,screening selection and optimization,a regional risk evaluation index system of landslide-generated impulse wave disaster with 20 indicators was built.On this basis,a regional comprehensive evaluation cloud model of landslide-generated impulse wave disaster risk was established,which comprised risk scale cloud,index semantic cloud,index value cloud,index weight cloud and risk comprehensive cloud.Finally,the cloud model was applied to evaluate the risk of landslide-generated impulse wave disaster for 17 administrative areas in the Chongqing section of the Three Gorges Reservoir Area by subjective weight method and objective weight method,respectively.Results showed that the landslide-generated impulse wave disasters in the Three Gorges Reservoir Area could be ranked between lower and higher levels of risk as a whole.In more detail,seven districts(including Yubei,Fuling,Changshou et al.)accounted for41.18% of all evaluated districts were between the lower and moderate risk levels,and six districts(including Jiangjin,Fengdu,and Wanzhou et al.)accounted for 35.29% of all evaluated districts were between the moderate and higher risk levels.The evaluation results can provide reference for the formulation of disaster prevention and mitigation policies of landslide-generated impulse wave disasters. |
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