| China’s karst area is widely distributed,accounting for 1 / 3 of the country’s land area,mainly distributed in southwest China.But these areas belong to the mountainous area,the transportation is inconvenient,in order to promote the local economic development,must build the bridge repair tunnel.Therefore,the construction of the project will face a lot of karst engineering problems,water inrush,mud,collapse and other engineering disasters,seriously affecting the safety of the project and construction progress.As the most common engineering disaster in karst area,water and mud outburst has become the frontier problem to be studied urgently.Taking the Diansha tunnel in Yunnan Province as the research object,the mechanical characteristics and Disaster Prevention Measures of outburst prevention layer in karst tunnel are studied by means of literature review,Field Monitoring,theoretical analysis and numerical simulation,it can provide information for the design and construction of Karst Tunnel in China.The related achievements are as follows:(1)the characteristics of karst development are studied by means of Literature Review and field investigation,starting with Karst Morphology,surrounding rock properties and geological structure,it is found that its development characteristics are mainly related to geological environment and rock characteristics,and its main influencing factors are groundwater,rock solubility and mineral composition,geological faults,distribution patterns and folds can lead to the development of large-scale Karst.(2)to study the damage mode and prevention measures of Karst Tunnel,and to investigate and count the typical cases of water and mud bursting disaster and its prevention measures,and to analyze the influencing factors of safety thickness of outburst prevention layer.This paper comprehensively analyzes the causes and modes of water inrush disasters,which can be divided into three disaster modes: Progressive Destruction,seepage instability and direct exposure of leakage,and sums up the prevention and control measures of water inrush disasters in China,the measures of advanced geological prediction,drainage,water plugging and structural reinforcement are analyzed and discussed.(3)based on the finite element method,the mechanical characteristics of the outburst prevention layer are studied by numerical simulation.Through monitoring and analyzing the stress,displacement and pore water pressure of surrounding rock in the outburst prevention layer under different working conditions and construction steps,it is found that the pore water pressure of the arch appears a steep decline trend during tunnel excavation,and decreases with the distance from the tunnel chamber,the criterion of the minimum safe thickness of theKarst Cave and the arch roof above the tunnel is put forward,when the pore water pressure of the outburst prevention layer decreases greatly,the water inrush disaster is easy to occur,and the outburst prevention layer is close to the minimum safe thickness.(4)the application and effect evaluation of disaster prevention and control are carried out in combination with on-site monitoring and measurement and disaster situation.The main disaster control measures are to clean up the mud pile by pipe roof grouting,to reinforce and excavate the face by pipe roof in advance,to optimize the construction measures and support parameters,to strengthen the surface drainage and reduce the environmental impact. |
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