Wearing course is the surface layer of the road, driveway or footpath. It provides a textured, and durable smooth riding surface.

[OED] Gloss. Highway Engin. Terms (B.S.I.) 31 Surfacing, the top layer or layers, comprising the wearing course and/or base course but not the base.

From two ecbc.ca documents:
La voie ferrée est construite de rails soudés de 115 lb. D’après le directeur général de CB&CNS, l’acier est dans un état allant de satisfaisant à très bon. Les traverses, la couche de roulement et la lutte contre la végétation ont en général souffert d’un manque de capital depuis 1998 et une certaine érosion de leur qualité s’est produite.

The rail in place is continuously welded, 115 lb. rail. According to CBNS’ General Manager, the steel is in fair to very good condition. Ties, surfacing and vegetation control have generally suffered from lack of capital since 1998, and some erosion of their quality has occurred.

While in the road sense "couche de roulement" is indeed "wearing course", etc., i.e. an engineered surfacing material to spread the load, keep water out, prevent rutting, provide skid resistance, etc., in mines I shouldn't think there are likely to be surfaced roads, hence your question, I imagine.

I therefore wonder if they don't mean "couche de ROULAGE", i.e. the layer of naturally-occurring rock over which the trucks haul ore. I am not familiar with the concept, but "roulage" is definitely a mining word for "haulage".