Underground Construction - Hydrogeology: Objectives, Methods, Applications - page 281

above the point where they plunge below sea level. Its structure consists
of recumbent folds and SW-NE overthrusts (Figure 132).
Figure 132 Monte-Carlo railway tunnel (Principality of Monaco). Geologic structure and
cross-section along the path of the tunnel.
The landscape is dominated by Jurassic carbonate promontories which,
above the plastic Triassic base, form duplex thrust anticlines, in stair-stepped
units or overriding scraps of Cretaceous marl and marly limestone. The
whole is cut up by subvertical transverse faults and, particularly, the sizeable
median Larvoto thrust fault. It should be noted that the overthrusting front is
totally obscured by scree slopes extending out to the sea in the northeastern
part of the area in question.
The Jurassic units make up the main karst aquifer in the area, with karst
circulations blocked at depth by the impermeable screen of the Triassic
and frontally barred by Cretaceous formations or tectonic upwellings of
Triassic.