Experimental study on dynamic effects of face stability in sandy-strata slurry shield tunneling

When a slurry balance shield advances through high-water-pressure sandy strata, the dynamic stability of the excavation face becomes a crucial factor governing tunneling safety. Previous research has largely focused on the stability of the excavation face under stationary cutterhead conditions, overlooking the dynamic interactions among the cutterhead, soil, and slurry. This study developed a physical model experiment system to evaluate the stability of the shields. It systematically examines the effects of the cutterhead rotational speed, hydraulic head conditions, and cutterhead structural configuration on excavation face stability. Experimental results show that cutterhead rotation has a significant impact on the distribution and fluctuation characteristics of pore water pressure. As rotational speed increases, the fluctuation period decreases and tends to stabilize when the speed reaches 3.0 rpm. Surface deformation reaches its maximum immediately above the excavation face. Moreover, higher rotational speeds lead to a broader propagation of the settlement trough toward the rear. Meanwhile, the filter cake develops not only along the excavation face but also progressively accumulates within the underlying soil. Under dynamic conditions, the filter cake surface exhibits roughness and uneven thickness. The excavation face exhibits a composite “logarithmic spiral-frustum” failure mode, and the instability zone expands with increasing rotational speed. In addition, cutterhead rotation substantially increases the ultimate support pressure of the excavation face. At 3.0 rpm, the ultimate support pressure rises by ∼8.4% compared to stationary conditions. This study highlights the significant impact of cutterhead dynamics on the stability of the shallow-buried slurry shield excavation face. The findings provide valuable insights and practical guidance for the safe construction of shallow-buried slurry shield tunnels in highly permeable strata.