Support Methods for Open Shields.

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 methods are applied to achieve support in the surrounding geology and also to prevent the machine from flooding. One option is the use of a device known as a hood shield, which extends the upper part of the shield. Here, the shield blade is adapted to the angle of the rubble in the geology to create permanent contact with the tunnel face.This prevents the ground from falling in from overhead and the associated subsidences.

Additionally, a transverse platform can be used to further reduce the angle of the rubble. The whole shield can also be designed as a 'poling plate system' whereby it is subdivided into several plates each of which can be extended forwards. This ensures that the rubble angle is always adapted as geology changes. In addition, extendable support plates can be installed, which can be pressed up hydraulically against the tunnel face where necessary as an additional safety measure.

When working in groundwater-holding soil, water penetration can be prevented by having the partial face excavation machine and a section of the tunnel protected by a lock system using compressed air. The required pressure is monitored continuously and adjusted automatically where necessary by a compressed air system consisting of two control circuits.