Page:Walker (1888) The Severn Tunnel.djvu/197

120 level from its eastern end for a length of rather more than a quarter of a mile, when two steam-navvies were brought upon the works, and started to take out the excavation. A shaft was sunk at a point rather more than a quarter of a mile east from the eastern tunnel face, where a public road and one of the main drains of the level crossed the railway.

At this point it had been originally intended to build an ordinary bridge; but after the lowering of the gradient, it was found necessary to execute a short length of tunnel instead of this bridge. The shaft was sunk for the purpose of constructing this tunnel.

The invert of this tunnel was just on the top of the red marl, and the whole of the tunnel itself in gravel, with great volumes of water. Above the gravel was soft running sand, and then mud.

It was ground that required the greatest care, and could only be safely executed by being kept perfectly dry.

Two 15-inch pumps were therefore fixed in the shaft; and before the end of the year a break-up was started in the middle of this tunnel, and about 20 yards of completed tunnel executed.

Before the end of the year rather more than a mile of full-sized tunnel was completed from the Sea-Wall Shaft. The arch was finished under the whole length of the ‘Shoots,’ and all but 100 yards from there to the Sudbrook Pit. The tunnel was