Research On Disaster Risk Assessment And Prevention Technology Of Pipeline Crossing Karst Area

The foundation of oil/gas pipeline in karst area would suffer flushing by karst groundwater flow,which will cause the foundation to be hollowed out,resulting in uneven subsidence,suspension and even cracking of the pipeline.The damage would be caused in the safe operation of the pipeline in the karst zone.The research on the risk assessment and prevention technology of pipelines through karst collapse area has a significant influence on avoiding and reducing the damage of karst area disasters to the West-East Gas Pipeline.At the current stage,there is no specific disaster assessment and risk assessment for karst areas in China and abroad.This thesis is based on the actual problem of karst collapse during the construction of the Nanning branch of the second line of the West-East Gas Pipeline.The current states of geo-hazards in several parts of pipelines were investigated by in-situ investigation and geophysical exploration.The morphology and distribution characteristics of karst collapses and their influence factors were analyzed.Then,an analytic hierarchy process is used to establish the karst collapse prediction and evaluation model,which were applied in the research area for the karst collapse risk analysis and assessment.After that safety management measures and support technologies were initially proposed for the prevention of geological disasters in the karst area.The research results show that the height of the underground cavern in the study area is between 0.2 and 17.6m,with an average of 2.5m.The burial depth of the karst cave is at least 0.9m,the maximum is 13.1m,and the average is 6.3m.The line karst rate ranges from 2.42%to 86.23%.The underlying bedrock karst collapse mainly occurred in the limestone formation of Devonian Donggangling.Pumping is the main cause of karst collapse after investigation of 114 collapse pits.Carbonate strata and Quaternary overburden are the main geological conditions for karst collapse.Groundwater lever fluctuating and human engineering activity is the dynamic conditions for the formation of karst collapse.Employed the GIS technology,10 parameters were chosen as evaluation indexes of karst collapse,including bedrock lithology,geological structure,line karst rate,soil thickness,groundwater level,groundwater level,and bedrock surface,pumping well influence,existing collapse,soil cave and soft soil.The analytic hierarchy process is applied to establish the karst collapse evaluation model,which was applied in the research area for the karst collapse risk analysis and assessment.The evaluation results indicate that the length of the extremely easy collapse zone is 25.897km,the length of the easy collapse zone is 20.878km.and the length of the easy collapse zone is 51.965km.Base on the semi-quantitative risk assessment method,the probability of risk occurrence,pipeline laying,disaster activities,design and misoperation were selected to establish a karst collapse risk assessment method system.The results show that:...At last,taking the West Second Line project as an example,after analyzing the characteristics of karst and the feature of the project,it is initially proposed that compaction grouting is the best way to deal with karst collapse and concealed soil cave.