The membrane must be fixed on a solid and flat support. If necessary, a strip of at least 20 cm must be rehabilitated using high-strength, quick-setting mortars.
If the side walls have sharp edges, it is advisable to smooth them using an abrasive disc.
It is preferable that the edge of the diaphragm is immediately above the ballast, avoiding large portions of uncovered diaphragm which could be damaged.
The membrane must be fixed on a vertical or inclined surface, avoiding fixings on horizontal surfaces which do not allow the removal of water.
JOINTS, FIXINGS AND FLAPS
In the case of multiple membranes, after laying them on the ground, the joints are made, either by overlapping or riveted, according to the project specifications and specifications.
Once any joints have been completed, the membrane is fixed along the ballast containment walls.
The membrane can be cut manually using well-sharpened cutters, preferably with a hooked blade, of the type indicated in the figure.
Also at the shoulders, the membrane must be turned up along the edges of the excavation, to form a sort of ‘tub’ whose edges must be kept no less than 35-40 cm from the intrados of the crosspieces.
Finally, before laying the crushed stone, it is necessary to make the water outlet holes in correspondence with the wells, taking care to match the holes with the wells.
RESTORATION OF THE BALLAST
The restoration of the ballast must be carried out using new crushed stone, of a quality compliant with the specifications, and well washed.
It will be necessary to proceed with the laying of a first layer of crushed stone, up to a level slightly lower than that of the crossbar intrados. The additional ballast will then be laid following the installation of the track spans.
