Study On Mechanical Response And Safety Of Composite Stratum Pipe Jacking Tunnel Crossing High-speed Railway Construction

At present,China has put into operation a total of 35000 km of high-speed railway,ranking first in the world.The development of China’s high-speed railway has led the world in all aspects.The construction of new projects in the limited urban underground space will inevitably be close to the high-speed line structure.Due to the extremely strict control requirements of the high-speed railway line structure for foundation settlement and structural deformation,there will be great difficulties and risks in the construction of underground projects close to the high-speed railway line.Pipe jacking method is an underground pipeline construction technology developed after shield method.Pipe jacking construction is widely used in urban underground tunnel engineering in recent years because of its strong adaptability of shallow land layer,high section utilization rate,safety and economy,small construction disturbance,environmental protection and many other advantages.However,at present,rectangular pipe jacking is mainly applicable to soft soil layer.The stratum and building structure encountered are relatively simple,and the construction section of pipe jacking is relatively small.When pipe jacking is constructed in the above complex stratum and complex structure,it will encounter many problems.Based on the large section rectangular underpass project in the west of Putian railway station,this paper makes comprehensive use of research methods such as data investigation,theoretical analysis and numerical simulation.The main research contents and results are as follows:(1)Taking the largest rectangular pipe jacking across the new Fuzhou-Xiamen high-speed Railway in China as the background,the paper uses the THREE-DIMENSIONAL finite element method to simulate the evolution process of the supporting structure system and its environmental impact under the two construction schemes of "pile-plate + pipe jacking method" and "pile-plate + shallow buried excavation method" for the underground passage on the west side of Putian Station.The influence of different strata and different construction methods on the excavation of large section shallow buried tunnel is analyzed and discussed from the aspects of surrounding rock deformation,surrounding rock stress,pile plate displacement and structural stress,and the advantages of pipe jacking method in structural safety control are illustrated,which provides a basis for the selection of engineering construction method.(2)PFC 3D discrete element method was used to calibrate the granular mesoscopic parameters of weathered granite stratum during the pipe jacking machine crossing,and a THREE-DIMENSIONAL discrete element numerical mechanical model of rock breaking by milling head and cutting arm was established.The mechanical response characteristics of pipe-jacking assisted rock breaking equipment at different speeds and jacking speeds were studied.The key construction parameters of pipe-jacking assisted rock breaking equipment were determined from cutting energy consumption and rated cutting force to ensure the efficient and normal operation of the equipment.(3)on the west side of putian wear pipe jacking tunnel under both high-speed lines,control the benchmark analysis under wear on the negative impact of the high-speed railway tunnel,ABAQUS finite element model is established,from the differential settlement,the difference of two rail surface subsidence along the track,analysis of the stress state of union head pressure,tube is discussed the influence law of friction coefficient and the distance between double line tunnel working face,Optimize pipe jacking construction parameters.