4. Deep horizontal confinement

Complete containment of a polluted site may sometimes require the creation of a watertight bottom, in the absence of a watertight natural substratum. Creating such an artificial bottom sealing system is a tricky business. It is necessary to design a watertight bottom and connect it to the lateral waterproofing system, either through the polluted area or directly from below.

To solve this problem, the approaches are as follows:

• the first is to consider it acceptable to work above the waste or polluted zone, which will be crossed by a suitable mesh of boreholes enabling a raft to be created either by conventional injection or by jet grouting;

• the second, on the contrary, favors an approach from below the site. In this case, the watertight floor is created using peripheral shafts, a tunnel...