Pressure exerted against the native soil.

Wherever the soil is unstable, support pressure needs to be built up at the tunnel face to equalise the pressure exerted by the earth and groundwater on the cutting wheel and to prevent the tunnel face from collapsing.

Wherever the soil is unstable, support pressure needs to be built up at the tunnel face to equalise the ambient pressure. Support pressure is needed to counteract the pressure exerted by the earth and groundwater and to prevent soil penetrating the tunnel face and any loss in stability.

Because of their open construction method, partial face excavation machines cannot build up any support pressure using a support medium when working at the tunnel face. Therefore, different alternative methods are applied to achieve support in the surrounding geology and also to prevent the machine from flooding.