Research of jacking force of densely arranged pipe jacks process in pipe-roof pre-construction method

Abstract

The tunnel crossing project of the Taiyuan Railway Station is constructed by using a pipe roof preconstruction method (PPM). The project uses 20 steel pipe jacks with a diameter of 2 m. The distance between the jacking pipes is 165–265 mm. In this study, the jacking force of densely arranged pipe jacks was studied by a large-scale similar model test and engineering measured data. Pipe jacking forces at different positions during the model test were analysed. The upper pipe jacks of the PPM interacted with the surrounding soil. The soil between the pipe jacks became tightly compressed, and an arched soil–pipe jack pseudostructure was formed (pipe–soil arching effect). A squeezing phenomenon was observed during the jacking process. The jacking force of the pipe below the waterline was reduced by water buoyancy. The formula for calculating the jacking force of the jacking pipe below the pipe arching effect was proposed. The passive soil pressure coefficient should be reasonable in the formula for calculating the jacking force. The formula for calculating the jacking force below the water level line was derived.