Abstract: In shield tunneling through clay strata, the stratum ahead of the tunnel face fractures owing to excessive slurry support pressure, with the fractures propagating to the surface. Understanding the propagation pressure and the path of soil fracturing is crucial for mitigating these issues. To this end, a large triaxial fracturing test platform is established to examine the slurry pressure and propagation path of soil fracturing. The study also considers the effects of slurry viscosity and stress conditions. The experimental findings indicate the following: (1) With low slurry viscosity, the fracturing pressure remains constant during the fracture propagation process. With high slurry viscosity, the fracturing pressure gradually increases during the propagation process. (2) Both the initiation and propagation pressures increase with slurry viscosity, although the rate of increase diminishes over time. The propagation pressure increases linearly with confining pressure, albeit at a slightly lower rate than the initiation pressure. (3) A comparative analysis of fracture inclination angles in blind hole samples under various conditions reveals that the inclination angle of fractures correlates only with the pressure differential between axial and confining pressures. (4) Practical recommendations for construction suggest maintaining slurry viscosity above 21 Pa·s. (5) When buried depth varies greatly, the slurry pressure should be adjusted in real time with significant variations in tunnel depth. (6) Following initial fracturing, a sharp drop in slurry support pressure occurs, suggesting that tunneling should be expedited rather than replenishing slurry pressure.

Key words: underwater tunnel, slurry shield, fracturing test, slurry viscosity, propagation pressure, fracture morphology