Friction Performance Testing Study at Rock-Pipe Jacking Interface under Mixing Rock Debris with Slurry

To address the issues of pipe stuck and sudden increase in jacking force in ultra-long-distance and large-cross-section rock pipe jacking projects, this paper systematically investigates the complex friction characteristics between pipelines and rocks under different rock debris gradations and different mixing ratios of rock debris to slurry using direct shear tests. The results show that: When the total mass of debris is low and the proportion of large particles is dominant, the debris creates a furrow effect on the contact surface, with the friction coefficient primarily controlled by the roughness of the contact surface. Conversely, when the total mass of debris is high and the proportion of fine particles is dominant, the debris interlocks with each other, and the friction coefficient is mainly controlled by the void ratio. Then, an inverse analysis of the jacking force in the field based on the test results was carried out using the improved jacking force prediction model. The validity of this study was eventually confirmed by the results of the field monitoring. The presence of rock debris is very detrimental to jacking, and the inevitable formation of "cake bentonite" conditions at a later stage leads to a sharp increase in frictional resistance. Accordingly, the site should be cleared of debris from outside the pipe strings in a timely manner and consider regular and continuous injection of lower viscosity bentonite slurry. The study results can provide new research ideas and methods for solving problems in this field.