Construction stability and reinforcement technology for the super-large rectangular pipe-jacking tunnel passing beneath the operational high-speed railway in composite stratum

The super-large rectangular underpass of the Putian Railway Station, driven by the rectangular pipe-jacking method, needs to bore cross under the operational Hangzhou-Shenzhen high-speed railway in the composite stratum. This paper aims to explore the construction stability and reinforcement technology of the super-large rectangular tunnel when excavating under the operational high-speed railway in the composite stratums. Firstly, the engineering background, the construction method, and the geological conditions are introduced in detail. Then, to evaluate the stability and safety of the construction, refined numerical models and the hard-rock ratio for the super-large rectangular pipe jacking tunnel in the composite stratum are proposed, and a construction risk assessment system comprising twenty risk factors is established. After that, three schemes are employed to guarantee the construction safety of the super-large rectangular tunnel and the high-speed railway, the reinforcement effect of schemes is derived by analyzing track stress, track settlement, safety factor, and risk re-assessment results, and the optimal scheme for the present project has been obtained. Finally, hand-dug piles + D-shaped beam has been employed for the adjacent construction of the Hangzhou-Shenzhen high-speed railway, the reinforcement technology and the automatic investigation system are proposed, thus the effectiveness of the scheme has been verified.