'Underground consolidation' is fine, even if I think 'underground' is unnecessary since it is obvious we're not talking about consolidating the building. Moreover, if it has been made clear in what precedes that the inspection générale des carrières is involved, I doubt 'underground' is necessary. But belt and braces, eh?

Otherwise 'ground consolidation' or 'sub-surface consolidation' might be a little less 'over-the-top' (ha ha).

"Historically the mitigation of shallow mine working hazards beneath the railway has involved ground consolidation, whereby grout is injected [your injection is 'grouting' - not the same in civil engineering as in construction where grout is the stuff you put between tiles] under gravity pressure through boreholes to fill any sub-surface voids so that sub-surface support lost by excavation can be replaced or maintained. This type of mitigation has proven to be very expensive in a railway environment."
https://www.networkrail.co.uk/wp-content/uploads/2019/06//Mi...


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Note added at 4 hrs (2023-05-11 21:03:40 GMT)
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Underpinning is not exactly the same thing. For starters, the French is reprise en sous oeuvre, and it is less 'general' than consolidation, being applied in specific locations such as beneath existing walls so that a basement can be deepened within those walls, for instance, or to increase the foundation strength when extra floors are added to a building.

"underpin To provide new, deeper support under a wall or column without removing the superstructure, so as to allow the load on the builmding to be increased, or to allow the ground inside or outside it to be lowered, or to prevent settlement of the foundation. It is the construction of foundations for a building which exists."
[Scott, Penguin Dict of Civil Engineering]

Since your text refers to grouting, here is an apposite definition where it is made clear that 'consolidation' refers to strengthening of soil/rock and is the opposite of the geotechnical meaning of 'consolidation' which means settlement of soil:

"consolidation grouting, compaction grouting, claquage grouting Unlike permeation grouting, this grouting method uses hight grouting pressures and changes the soil structure by forcing tongues of ground into the soil. The appreciable surface movement [which should be avoided] may be troublesome, but the soil may be strengthened."
[idem]