How does soil conditioning with polymers affect the performance of an EPB TBM in clay soils?

Polymers are used in soil conditioning for EPB TBMs in clay to modify the soil properties, which improves the TBM's performance in several ways. First, they reduce the clay's stickiness. Clay soils are naturally cohesive and stick to metal parts of the TBM like the cutterhead and screw conveyor. This causes clogging and requires more torque to operate. Polymers coat the clay particles, reducing adhesion. Second, they improve the soil's workability. This means the soil becomes easier to handle and control inside the TBM, allowing for more precise pressure management at the tunnel face. This is key for maintaining face stability and preventing collapses. Third, polymers can reduce permeability. Clay soils often have high water content, which can destabilize the face. Polymers bind to the soil particles, creating a less permeable mass that reduces groundwater inflow. Finally, they help form a stable plug in the screw conveyor. The screw conveyor controls the rate at which excavated soil is removed from the TBM. Polymers help the soil form a cohesive plug that prevents uncontrolled discharge and pressure loss at the face. Soil conditioning involves mixing additives with the soil being excavated to improve its properties. An EPB TBM, or Earth Pressure Balance Tunnel Boring Machine, maintains face stability by balancing the pressure exerted by the machine with the earth pressure of the surrounding soil.