Mechanical Response And The Control Of The Crossing Existing Underground Structure With Conventional Tunnel Construction

Because of the different construction period,there are more and more cases of the new tunnel crossing existing structure in construction of urban rail transit.The safety for underground structure influenced by construction has become one of the key issues of urban rail transit.Therefore,there is an important practical significance to analyze the mechanical response and process control of underground structure under the new tunnel construction.With a large number of engineering practice of new tunnel crossing existing underground structure,this dissertation analyzed the deformation law of new tunnel crossing existing underground structure,mechanical response of underground structure under the influence of group tunnel construction,deformation control standard formulation based on damage degradation analysis,adaptability analysis of construction scheme and safety control technology by the method of case statistics,theoretical analysis,numerical simulation,monitoring and so on.The result shows as follows.(1)Based on engineering examples,analyzed the whole deformation of underground structure under the influence of new construction crossing of the whole tube and a single tube.The study shows that the settlement of whole existing station is flexible.The structural deformation between the two blocks includes overall settlement,vertical flex,vertical rotation,relative reverse and joint dislocation.The worst condition is induced by overall settlement,vertical flex.And relative reverse is occurred after the construction.The vertical rotation is occurred during the construction.(2)Based on stochastic medium theory,derived formation for deformation calculation formula of circular section,elliptic section,rectangular section and the straight wall arch section in single hole and double hole cases.Take Chaoyangmen-Dongdaqiao section(double hole with a rectangular section)of Beijing subway Line 6 for example,analyzed the surface deformation under the influence of construction with bench method,multi heading excavation method,hole pile underpinning method and CRD method.With two-stage analysis method,calculated the mechanical response of underground structure under the influence of tunneling construction and analyzed the corresponding influencing factors.The research results provide the datas supporting for the maximum deformation prediction.(3)Through the collection of the cases of injured or cracking tunnel structure in Beijing,The relationship between damage or deterioration of underground structure and operation history has been established on the basis of the research on the damage mechanism of structural cracks,steel corrosion,concrete carbonation,surface damage of concrete,concrete strength attenuation and so on.Meanwhile,the method of determining the control standard of the existing underground structure is proposed based on the damage degradation of the needle.At last,the quantitative reduction of the control standard of the existing underground structure can be realized.(4)Based on the engineering example and two-stage analysis method,extablished the 3-demensional relationship of existing underground structure,construction plan for new tunnel and the maximum deformation.Considering the geological condition,the size of new tunnel,the construction method(including auxiliary method),the distance between the roof of the new tunnel and the existing underground structure bottom,the existing underground structure section size and buried depth,proposed the maximum deformation prediction method for the underground structure.Proposed the conception of suitability of construction plan,three step of suitability analysis and fitness formula.At last,classificated the suitability(5)On the basis of the above research,established the control system of the construction process.The system consists of three stages:"pre-construction optimization of construction scheme","dynamic control in construction","evaluation and recovery after construction".The technological process considers the characteristics of damage and deterioration of existing underground structures,and chooses the appropriate construction scheme according to the analysis of adaptability.The system can achieve the subtle control of the crossing construction.The method has been used in the construction of Chaoyang-Dongdaqiao section crossing the existing station in Beijing Subway Line 6.