Complex sentence: Sandy and porous geology down to about was waterlogged and about 36 boreholes around each shaft position had subzero temperature brine pumped through them which froze the ground down to about.
Split into simpler sentences: Sandy and porous geology down to about was waterlogged. About 36 boreholes around each shaft position had subzero temperature brine pumped through them, which froze the ground down to about.