. Manual for railroad engineers and engineering students : containing the rules and tables needed for the location, construction, and equipment of railroads as built in the United States . The Sydenham Tunnel, on the London, Chatham, and DoverRailway, is 2100 yards long, and is made through the Londonclay. It had seven shafts, varying from 50 to 186 feet in depth,and 9 feet internal diameter. Two only of these shafts wereintended to be left open permanently. The clay in which thiswork was executed, though yielding freely to the pick, afterwardsswelled, and crushed the masonry. The shafts were
. Manual for railroad engineers and engineering students : containing the rules and tables needed for the location, construction, and equipment of railroads as built in the United States . The Sydenham Tunnel, on the London, Chatham, and DoverRailway, is 2100 yards long, and is made through the Londonclay. It had seven shafts, varying from 50 to 186 feet in depth,and 9 feet internal diameter. Two only of these shafts wereintended to be left open permanently. The clay in which thiswork was executed, though yielding freely to the pick, afterwardsswelled, and crushed the masonry. The shafts were made 9 feetin diameter, but were afterwards pressed in so as to be hardlymore than 6. The headings were 4x6 feet, and were run for- 94 MANUAL. FOR RAILROAD ENGINEERS. ward at the top, and not the bottom, of the excavation. Theoriginal section is shown in Fig. 34. But the swelling of the clayso forced in the masonry that 6780 cubic yards of the side walland 2065 yards of the invert had to be rebuilt. At the foot ofone of the shafts, 120 feet deep, which was the worst place, thetunnel was at first lined with eight rings of bricks, making a. Fig. 34- thickness of 36 inches. This was cut out and replaced, first byten, and again by twelve rings of brickwork, or 4 feet 6 inchesof thickness ; and even some of the last had to be replaced. Theshafts had at first alining of brick 9 inches thick ; but this was sopressed in, and the diameter so reduced, as to require a newlining 18 inches in thickness. This action of the clay begins very soon after the excavation ROCKWORK AND TUNNELLING. 95 is made ; if it is not noticed within two months, it is no longerfeared. The action at the top of the arch is slight, the principaleffect being on the invert, which rises first in the centre, andafterwards at the sides. The dotted line in the figure shows thealtered shape of the original section. The form was afterwardschanged ; the first step being to lower the invert, which showedsuch a tendency to ri
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Keywords: ., bookcentury1800, bookdecade1880, bookpublisherbosto, bookyear1883
