Page:Walker (1888) The Severn Tunnel.djvu/89

36 fissures, yielding immense quantities of water, the water spouting through the fissures under a head of about 100 feet; and it was not till the 18th July that the shaft reached the bottom side of the bed, and entered the fire-clay shale, which proved to be perfectly dry. The bottom of the tunnel was reached at the end of July, and profiting by the experience which we had obtained at Sea-Wall, we drove a cross-heading 4 feet 3 inches below the level of the invert of the tunnel in the direction of the pumping-pit. From this heading we sunk the bottom part of the pumping-pit in shale, which was perfectly dry till we reached within a few inches of the bottom, where a small spring was met with, which evidently was under a pressure of at least 100 feet.

By putting in a small iron pipe to allow this water to rise into the cross-heading, we were able to complete the brickwork at the bottom of the pumping-pit before we allowed the water from the conglomerate above to come down upon it. When this brickwork was completed and the cement properly set, a bore-hole was put in down the centre of the shaft, and the water allowed to flow into the bottom of the pumping-pit and through the cross-heading to pumps fixed in the line of the tunnel. The shaft was then completed, both as to sinking and brickwork. The pumping during the sinking of these pits had been done by a variety of pumps, but finally by a 15-inch bucket-pump. While the shafts were being sunk a large