The Key Technology of Large Diameter Shield Tunn...
The construction of large diameter shield shallow overburden is one of the difficult problems in the construction process of river tunnel at present.Once something happens，the loss will be inestimable.Therefore，it is of great significance to improve and perfect the construction technology of large diameter shield shallow overburden.
This chapter first introduces the difficulties and technical status of large diameter shield shallow overlying soil construction，and focuses on the parameters and main technologies of shield shallow overlying soil excavation，including the construction technology of shield shallow overburden in the initial and arriving section，the shallow overburden shield construction technology through the bottom of the river，the incision water pressure control，the shield plane elevation attitude control，the mud water quality control and the synchronous grouting control behind the wall，etc.The slurry split（instability mechanism of excavation surface）is discussed，and finally，the three-dimensional visual simulation technology of shield shallow overburden excavation construction is introduced.
When the tunnel passes through the shallow overburden section at the bottom of the river，due to the requirements of the tunnel design line，the overlying soil layer of the tunnel will be shallow.When the overlying soil weight and river pressure cannot resist the floating force of the tunnel caused by grouting in the process of tunnel excavation，the tunnel will float or fall off the roof，which will bring inestimable disaster to the project.When the thickness of overlying soil layer is less than 1.0-1.5D（D is the outer diameter of excavation），the problem of overlying soil in tunnel must be studied.At home and abroad，there are many examples of similar difficulties in the construction of shield tunnel.In the process of shallow overburden construction，it is of great significance to solve the balance problem between the surrounding soil of shield and the shell of shield itself，which is of great significance to the shallow overburden caused by tunnel crossing through inland rivers.
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J.Chen et al.，Construction Technology of Large Diameter Underwater Shield Tunnel，Key Technologies for Tunnel Construction under Complex Geological and Environmental Conditions，https://doi.org/10.1007/978-981-16-5896-9_3