ENGINEERING. 



Wyo and the Great Western Railways at Lyd- 

 ney, crossing the river on a bridge three quar- 

 ters of a mile long, and terminating at the Sharp- 

 ness Docks, where it forms a junction with the 

 Midland Railway. After much delay, owing 

 to conflicting pecuniary interests, the works 

 were commenced in 1875. The construction 

 of the bridge has taken four years. Its total 

 cost was 200,000; the railway and approach- 

 es, including a tunnel a quarter of a mile long 

 on the Lydney side, cost an equal amount. 

 The total length of the bridge is 4,1 62 feet. 

 The width of the river at the crossing is 8,558 

 feet. The bridge is in 85 spans. On the Lyd- 

 ney shore 13 of the spans are arches of heavy 

 hammer-dressed stone, 12 of them semicircu- 

 lar, and one elliptical with a span of 52 feet. 

 They rest in alluvial deposit on foundations of 

 concrete. In the river the spans are bow-string 

 girders. One of these forms a swing-bridge on 

 the opposite side, hanging half over the canal 

 and half over the shore. The length of the 

 swing-bridge is 197 feet, the depth of its gird- 

 ers 19 feet 4 inches; the bridge weighs 600 

 tons, and turns on an arrangement of conical 

 rollers called a live ring, being carried upon a 

 circular pier of strong masonry. The motive 

 power is supplied by a steam-engine in an 

 engine-house resting on the top of the girders, 

 which contains also a reserve engine connected 

 with reserve machinery to provide for any 

 accidental stoppage of the regular machinery. 

 The turning and locking are accomplished by 

 friction-gearing so arranged that the turning 

 and locking apparatus can never be in gear at 

 the same time. The locking is accomplished 

 by two large iron wedges at each end of the 

 bridge, which are driven home in opposite di- 

 rections by rods connected by toggle-joints 

 with great iron bars, which advance longitu- 

 dinally with the bridge, and, extending be- 

 yond the wedges, enter sockets in the piers, 

 thus trimming the rails. An indicator in the 

 engine-house, which shows the engineer the 

 position of the wedges, also serves to break 

 the telegraphic connection, so that the bridge- 

 man can not signal a train to advance unless 

 the bridge is in position and locked. Besides 

 the swing-span, the iron part of the bridge 

 consists of 21 spans. The first span, adjoining 

 the masonry on the Lydney side, is 134 feet 

 long, with girders 16 feet deep. This carries 

 the bridge to the edge of the deep channel of 

 the river. Then the two main spans, 827 feet 

 long, with girders 39 feet deep, carry it over 

 the navigable river at a clear height of 70 feet 

 above high water. The next five spans are 

 171 feet long, with girders 20 feet 4 inches 

 deep; the last 13, 134 feet long, with girders 

 of 16 feet 9 inches. The elevation gradually 

 decreases from 70 feet over the main channel, 

 near the north side, to 50 feet in the clear over 

 the water at the swing-bridge on the Sharp- 

 ness side. All the girders are on the bow- 

 string principle ; the curved boom has a trough 

 section ; the tension-chord is composed of flat 



bars riveted together; the vertical compres- 

 sion-joints in the aide of the girders are 12 feet 

 apart, and are connected with the cross-gird, 

 ers, to which the strong rail -bearers are also 

 riveted. The floor is composed of w rough t- 

 iron plates riveted to the cross-girders and the 

 rail-bearers. The swing-span is 24 feet 6 inch- 

 es wide in the clear ; the other spans of the 

 bridge are adapted only for a single track, be 

 ing 14 feet 6 inches in width. The piers which 

 support the bridge are composed of cast-iron 

 cylinders, 6 to 10 feet in diameter. They were 

 made in 4-foot sections, and bolted together 

 through flanges on the inside. They were sunk 

 to a solid foundation, penetrating the bottom 

 rock from 4 to 15 feet. The cylinders which 

 compose the piers are of cast iron, 1 J to 1^ inch 

 thick. The piers which support the two main 

 spans are formed by four cylinders each, 10 

 feet in diameter below low water and 7 feet 

 in diameter above ; the diameter of the cylin- 

 ders supporting the five 171-foot spans is 9 

 feet below and 7 feet above low-tide mark ; 

 the remaining piers have a uniform diameter 

 of 6 feet. The piers are composed of two cyl- 

 inders each, except the three supporting the 

 two long spans. The greatest dimculties were 

 encountered in fastening the scaffolding for 

 the piers and the girders. Beginning to sink 

 the piers on the south side, it was possible to 

 excavate from the interior of the cylinders 

 until the twelfth pier was reached, after which 

 compressed air was employed. From this 

 point, after many unsuccessful attempts to 

 sink the scaffold-piles in the shifting sand, 

 with the strong tide bearing down upon them, 

 the problem was finally solved by the use of 

 Brunlees's system of sinking piles in sand ; that 

 is, by carrying a gas-pipe down to the foot of 

 the pile, and forcing a stream of water through 

 it strong enough to displace the sand and allow 

 the pile to sink. "While placing the fourteenth 

 and fifteenth piers, the staging and cylinders 

 were swept away together by the tide. Equal 

 difficulties were overcome in sinking the re- 

 maining piers. In the channel, with the tide 

 30 feet high and flowing 10 knots an hour, and 

 a depth from high water to bed-rock of 70 feet, 

 the task seemed almost impossible to accom- 

 plish. The sand was scoured away here so 

 that only a few feet remained ; but fortunate- 

 ly there was a layer of firm gravelly clay over 

 the rock, which gave the piles of the gigantic 

 scaffolding a firm hold. The staging was swept 

 away once or twice ere it could be secured. 

 When in place the 4-foot lengths of the cylin- 

 ders were lowered by screws and chains, and 

 excavation was carried on inside them by divers. 

 They were then built up to 12 feet above high 

 water, and until they would sink no deeper in 

 the sand. The air-compressing apparatus by 

 which the piers were sunk to their foundations 

 was in the shape of a bell, and was bolted to 

 the top of the cylinders, and provided with air- 

 locks for the entrance of the workmen ; the 

 pressure was from 5 to 40 Ibs., the latter pros- 



