A Possible Mitigation Strategy to Avoid the Collapse of Old

Multiple Choice

A possible mitigation strategy to avoid the collapse of old coal mine adits or tunnels is to fill them with sand to support the roof.This strategy was employed in old gold mines in Timmins,Ontario.What happened over time to make this strategy ineffective?

A) Pore water pressures within the sand increased and caused liquefaction subsurface.
B) Some of the sand washed away and no longer supported the tunnel roofs.
C) The sand settled and compacted, leaving voids into which the roofs collapsed.
D) The sand displaced subsurface water, raising the water table and flooding parts of the surface.
E) The sand allowed water to flow freely through pore spaces, dissolving more material from the mine walls.