M-13.1, r. 2 - Regulation respecting mineral substances other than petroleum, natural gas and brine

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102. Reinforced concrete slabs used to seal off or cover the access to a mine must be placed on the concrete of the rims or directly on the bedrock where the openings are not made of concrete.
Where a slab of reinforced concrete is laid or cast directly onto the rock of the opening, the space between the latter and the surface level must be backfilled with sand, gravel or other similar material.
O.C. 1042-2000, s. 102.