Shallow underground working system - places open-bottom caissons on surface and lowers by undercutting to desired depth

摘要

The underground working system consists in placing on the ground or on the bottom of a shallow trench caissons (1) open at the bottom. These are then lowered by undercutting to the level of the foundation of the tunnel to be excavated. - Excavation can be so carried out that the caissons sink under their own weight e.g. by using a loading shovel etc. at the centre. Near the walls controlled lowering is effected by hand digging or the use of small machines.