Engineering Wonders of the World
Volume I

82 ENGINEERING WONDERS OF THE WORLD. and it was necessary to send down a diver to put things right. When the pumps started again one of those in the Old Pit gave way, and it soon became apparent that the capacity of the pumps was not equal to overcoming the leakage of water past the shields ; and further attempts were accordingly postponed until a new and very large pump should have been added to the equipment. Sir John Hawkshaw now decided to lower was to remain the new centre line of The Gradient altered. have to run 15 feet below SIR JOHN HAWKSHAW, F.R.S., Engineer-in-Chief of the Severn Tunnel Works. {Photo, Rischgitz Collection, from a painting by James Edgdl Collins.} brought operations to so abrupt a standstill. Two large vertical shields of oak, having one face shaped to the curve of Checking the ]jnjng of yie Old pit, were ~ . constructed, lowered down Great Spring. the shaft, and adjusted by divers, so as to block the openings of the headings into the shaft. They were held firmly up against the brickwork by stout cross beams wedged between them (page 81). In spite of the difficulties caused by the great water pressure on the divers, the shields were in position a few days after the start, and backed with bags of Portland cement carried through flap-doors in the woodwork. The door between the two pits was then closed, and pumping commenced in the Iron Pit to lower the water sufficiently to permit the repair of the pump that had failed. Un- fortunately, the packing round the door leaked, the tunnel 15 feet under the Shoots, and alter the gradient on the Monmouthshire side from 1 in 100 to 1 in 90. As the gradient on the Gloucester- shire side same, the that part of the tunnel would parallel to the original line, but it. Furthermore, in order to avoid increasing the total length of the tunnel, it was necessary that the depth of the Gloucestershire entrance cutting should be also increased 15 feet, which entailed the removal of 550,000 cubic yards of stuff more than had been originally estimated. A third shaft, 18 feet in diameter, was com- menced at the Sudbrook end, close to the Old and Iron Pits, over the line of the tunnel. This was to be used for winding pur- poses. At a depth of 40 feet sinking opera- tions had to be stopped for a time, owing to leakage from the adjacent pits ; and the engineers had to content themselves with making a bore hole down to the heading below to drain the pit as soon as the works should have been emptied of water. Two new shafts were also begun somewhat westwards of the point where the Great Spring was tapped—the one for winding, the other for pumping. The first of these gave a great deal of trouble, for it encountered fissured rock, from which water spouted in immense quantities. Profiting by experience, the workmen heading from the bottom of this pit into the Interesting Shaft- sinking Operations. drove a cross