5. Tunnel boring machine guidance

5.1 Locating the machine in space

Whether it's a hydraulic or passenger transport structure, the positioning tolerance must meet the requirements of the structure to be built. For the most common structures, the positional tolerance of the tunnel axis is around 10cm on the radius. This tolerance covers all the geometric deviations that may occur between the projected and the final structure. These include :

• manufacturing tolerances for tunnel segments;

• their tolerance for installation in the TBM;

• their possible deformation under the influence of mortar injection or ground loads;

• the topographical imprecision of knowledge of the position...