toit supérieur

CONT: S'il s'agit d'une taille à foudroyage, le toit immédiat casse et s'effondre le long d'une ligne parallèle au front de taille à quelques mètres de celui-ci; les éboulis foisonnés remplissent le vide, de sorte que le toit supérieur, à quelques mètres au-dessus, repose sur ces éboulis, qui jouent le rôle d'un remblai, et les tasse progressivement [...]
PHR: Cassure d'affaissement, cassure d'exploitation (du, au) toit.

CONT: There are two broad types of roof as far as support is concerned, the immediate roof above the coal and the main roof. Artificial support for mining purposes is only concerned with the immediate roof as nothing except large blocks of solid coal, or massive concrete, will support the main roof. ... Main roof is composed of strata above the immediate coal bed roof that forms the overburden to the surface. Frequently, the term is applied only to a massive, strong rock layer that does not break or bend until all of the coal is removed by pillaring or by longwall mining.
OBS: Immediate roof: Lowest layer or layers of rock immediately above an underground opening.