Functions

The SPB developed by CREG precisely regulates supporting pressure via automatically controlled air cushions. It is capable of safely operating in complex heterogeneous strata and high water pressure up to over 15 bar even with super-large excavation diameters.

During SPB tunneling, a highly impermeable membrane forms at the interface between soil and bentonite suspension. This membrane establishes required supporting pressure and seals the excavation face to prevent groundwater inflow. To ensure precise face pressure control, a partition divides the slurry-filled chamber into the front excavation chamber and the rear intermediate working chamber. Pressurized air bubbles inside the intermediate chamber generate supporting pressure and transfer it to bentonite suspension. The two chambers are interconnected via openings at the bottom of the tunnel for fluid circulation.

Based on the closed hydraulic slurry circuit, the slurry shield can operate safely under water pressure exceeding 15 bar. This requires proper sealing matching between the atmospheric-pressure sections of the machine and the front ground strata, which is why the slurry shield is equipped with multiple sealing systems.
Its drive system features an independently sealed chamber filled with pressurized sealant. At the machine tail, the annular gap between the atmospheric-pressure tunnel and segment outer surfaces is protected by multiple rows of wire brushes filled with sealant, preventing ingress of soil and water.