Effects of Pipe Roof Support and Grouting Pre-Reinforcement on the Track Settlement

Based on the first shallow tunnel passing below an active railway station in the loess area in China, studies on the tunnel deformation and track settlement during tunneling are performed by using FLAC3D. It is found that, without adopting other reinforcement measures, the maximum track settlement has far exceeded engineering requirements. To reduce deformations induced by the tunneling, the combined presupport technique of the pipe roof and grouting reinforcement is presented and optimal construction parameters are provided. It is concluded that the installation of the pipe roof support plays an important role in controlling tunnel crown settlement and track settlement. The optimal pipe diameter is 159 mm, and the optimal arrangement area of the pipe roof is 150°. Grouting could improve soil strength and reduce deformations. The optimal thickness of the grouting reinforcement ring is 2 m. When the optimal parameters of the combined presupport technique are adopted, calculation results show that the maximum track settlement would reach 13.8 mm, which realized the settlement control goal of a maximum value of 15 mm. At last, the combined presupport technique proposed has been well validated in the “Railway Station” of Metro Line 4.

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