Shafts in Shale
Shale is a horizontally bedded soft rock, typically with limestone seams, that is prevalent in Southern Ontario. Blasting is rarely allowed in most municipalities, but shafts in shale can be readily excavated with mechanical equipment. Depending on the quality and degree of weathering of the shale, the treatment of the shaft walls can vary from nothing required to mesh held by pins to protect the workers in the shaft, to full shotcrete coating.
The degree of wall treatment is determined by the engineer-of-record after a site inspection. Support of any overburden above the shale requires a different treatment appropriate to that soil type.