"The old tunnel having been on a level and open at its extremities whatever percolation of water entered it either from the sides or above flowed out at both ends. The crossing of the new tunnel in no way affected this drainage...so the soil (a black Clay) continued firm enough to support the brickwork laid upon it. But by the filling up solid of a portion of it, leaving a hollow interval...the accumulation of water in seeking an egress has entered into, saturated, and sodden the clay on which the new Tunnel stands, and it is now incapable of supporting its weight."