Separating the Bottom of the Piston
One of the most difficult tasks during construction of the Gravity Storage is separating the bottom of the piston. For this to be successful without collapsing of the cover that is lying above, this procedure is performed in two steps.
In the first step, a channeling machinery creates a first grid of tunnels, each offset by a digging distance (see graphic). The top and bottom of these tunnels are coated with a sealing film and over that, a protective layer of concrete is applied. Then, these tunnels are filled with excavated material. If necessary, concrete pillars can also be installed in the tunnels so that the piston has sufficient support.
In the second step, the remaining grid of the rock web is cut free and also sealed.
The bottom of the piston is separated before the complete exposure of the outer walls so that as little stress as possible develops in the rock.