Theoretical Analysis on the Effectiveness of Pipe Roofs in Shallow Tunnels

Abstract

When a pipe roof is used as a pre-support for the surrounding rock in a shallowly buried tunnel, accurate prediction of the support effectiveness of the pipe roof is important in order to ensure the rationality of the pipe roof structure design. Based on analysis of pipe roof pre-support effects, considering the construction time of pipe roof structures and the interaction mechanisms between the steel pipes of the pipe roof and the surrounding rock, we establish a calculation model of the surrounding rock pressure acting on each steel pipe of the pipe roof on the semi-circular pre-support boundary. Through comparison and analysis with the measured results, we demonstrate that the calculation model for surrounding rock pressure and the calculation model for stress and deformation of the pipe roof are reasonable. According to the deformation coordination conditions between the steel pipe of the pipe roof and the surrounding rock on the pre-support boundary and alongside the Peck formula, we establish a theoretical analysis method for pipe roof pre-support effectiveness based on the indexes of the ground loss rate, settlement trough width, and maximum ground surface settlement, thereby realizing a quantitative evaluation of pipe-roof pre-support effectiveness. At the same time, the effects of steel pipe diameter, circumferential spacing, and excavation footage length on the pre-support effectiveness of the pipe roof are analyzed. The conclusions can be used as a basis for the design and optimization of pipe roofs and as a guide for the application of pipe roofs.

Numerical Model for Rectangular Pedestrian Underpass Excavations with Pipe-Roof Preconstruction Method: A Case Study

“…Many researchers have carried out extensive research on the application and support ability of the PPM and put forward numerous technical improvement schemes [5,9,[20][21][22][23][24][25][26][27][28][29][30][31][32][33]. Yang et al [5] presented a case study of ground and tunnel deformations caused by the excavation of a pipe-roof pre-construction tunnel.…”

“…The measured data were consistent with the numerical simulation results, which verified the reliability of the numerical simulation results. Li et al [27] proposed a theoretical analysis of the effectiveness of pipe roofs in shallow tunnels. Through a comparative analysis with the measured results, it was proven that the calculation model for surrounding rock pressure and the calculation model for the stress and deformation of the pipe roof were reasonable.…”