What Does Face Pressure Mean?
Face pressure refers to the pressure applied to the face of a tunnel due to loads on the soil layers in front of and above the tunnel face. These pressures are lateral in nature and their intensity is determined by several factors including:
- Depth of the tunnel
- Diameter of the tunnel
- Groundwater level
- Soil properties
- Infrastructure above the tunnel bore
Trenchlesspedia Explains Face Pressure
The pressure acting on the tunnel face originates from two sources:
Pressure from the soil layers to the front of the face - This comprises of lateral earth pressure, also called active earth pressure and pressure due to the level of groundwater.
Pressure from soil layers above the face – This comprises of lateral pressure due to the weight of the soil and the load exerted by infrastructure above the tunnel face. The overall term for these pressures is called surcharge pressure.
To counteract face pressure, stabilization methods such as bentonite slurry shields, compressed air and earth paste are employed at the face of the tunnel.