5. Description of field treatment techniques

To cope with difficult geological conditions, ensure ground stability and control the deformations generated in the massif, it may be necessary to implement ground treatment techniques prior to digging or advancement.

Moreover, in the specific case of tunnel boring machines entering or leaving already excavated stations or shafts, ground containment can only be effective when the first or last segment ring is keyed against the retaining wall. In this case, land treatment is typically carried out to create an improved and/or watertight soil mass to guarantee the stability of the face and limit surface deformations. The treated section is generally widened by 2 to 3 m on either side of the excavated diameter, and the length of the treatment corresponds to that of the shield, also extended by 2 to 3 m.

The main techniques used are described...