Risk Assessment And Prevention Of Snaping Rockfall In Banbishan

This paper takes Chengde city banbishan protection engineering project.Based on the field investigation,experiments,finding out the development and distribution rules of banbishan collapse,analysis of rock mass in the circulation type tensile rupture mechanism under the condition of freezing thawing,then from the angle of risk and vulnerability,risk analysis of dangerous rock collapse after the evaluation,the threat range and moving distance for the prediction and risk quantification,feedback to the actual project,the better measures are proposed,the risk analysis research through the whole process of engineering construction and use.The main results of this paper are as follows:(1)Characteristics of the distribution of geological disasters in the researched regionGeological environmental data and field investigation indicate that: Collapse is a major form of geological disasters along the roads,Characteristics of the distribution of geological disasters is mainly influenced by climate conditions,geomorphology,lithology,rock mass structure.Because of strong frost weathering,erosion and lithology,snapping is the main collapse pattern in high altitude area.(2)Influence factor and deformation characteristics of freeze-thaw in fissured rock massThe low temperature strain test indicates that: the strain curves of fissured rock with different crevice in a cycle time are significant different.after several freeze-thaw cycles,Micro residual strain of the fissured rock mass tends to accumulated increasing.(3)Physical and mechanical characteristics of frozen-thawed rocks(1)Physical characteristics: The rock samples which whether dry or saturated through the different cycles of frozen-thawed cycle tests show no obvious signs of failure.Quality and wave velocity variation caused by freeze-thaw action,is quite small.(2)Mechanical characteristics: Phyllite and sandstone,varying levels of hardness,resulting in their destruction of the specimen under uniaxial compression forms,Phyllite occurred along phyllitic cleavage and sandstone dominated by shear failure.The uniaxial compressive strength of the rock samples with different moisture intends to decrease along with increase of cycles.and the uniaxial compressive strength ratio tends to increase.The tests also indicate that attenuation amplitude of saturated rock samples is obviously larger than dry samples'.(4)Risk is an important segment of risk assessment,it directly relate the possibility of disaster of crag and the possibility of reaching to the protective porject.In order to evaluate the risk in geological disaster area,useing information-theoretic method to evaluate 5 factors include lithology,geological structure,weathering load,hydrological conditions,vegetation coverage and then,we decide the ratio of different factor.RHRS method is used to examine factors include geology,topographic feature,meteorology and hydrology,rock cutting size,the collapse scale and its history of collapse to evaluate the risk of slop.Finally,we combined dangerous factors that are used in which may cause disasters into an entirety.Those two evaluation methods evaluate the risk of the whole line from regional view and single point of view.Combining two evaluation methods and classifying based on evaluation criterion put forward by Pierson,we can evaluate the risk of slope accurately and directly.(5)vulnerability classify according to the type of hazard-affected body,and is used to evaluate fixed hazard-affected bodyand unfixed hazard-affected body.Firstly,we should calculate the impact force when a rolling stone reaching the building.secondly,we figure out the ultimate value of impact resistance bearing capacity in parts such as bridge deck,pier,and so on.Thirdly,we contrast the impact force and impact resistance bearing capacity,and quantize the vulnerability of fixed hazard-affected body into probability.Combined Peila and Guardini event tree method,we figured out the death rate of accident caused by collapse like traffic congestion,rolling stone accident,pavement damage and so on.(6)According to the hazard assessment and vulnerability assessment,we can accurately evaluate the risk of the construction talked in this paper.We put forward protective measures.