Field mechanical properties of large section concrete pipes during jacking in fractured moderately weathered siltstone

In the construction of pipe jacking, due to the effect of jacking force, slurry pressure, axis deviation, stoppage and geological conditions, the mechanical behaviors of pipe are very complex. Additionally, most of the calculation models of pressure around the pipes in the existing standards only consider water and earth pressure, which is different from the actual situation. Therefore, this work aims to reveal the mechanical properties of concrete pipe during jacking and explore the calculation method of jacking force and frictional resistance. Based on the field monitoring of the pipe jacking project for utility tunnel in Hubei, China, the variation law of the contact pressure, slurry pressure and pipe strain were analyzed, and the jacking force and frictional resistance were calculated through the above parameters. The results show that it is more appropriate to use the rock collapse height instead of Terzaghi theory to calculate the earth pressure at the pipe crown in fractured rock mass. There is a significant negative correlation between the slurry pressure around the pipe and the jacking force. In the stratum with high permeability, choosing an appropriate lubricant injection interval can effectively improve the lubrication effi-ciency and reduce construction cost. In addition, the axial strain of pipe can reflect the variation of the jacking force, and the frictional resistance calculated by the effective earth pressure is closer to measured value. The calculation methods and related conclusions proposed in this paper can provide a valuable guide for pipe jacking in fractured rock mass.