The three great European railway tunnels which have been described find their nearest counterpart in America in the Hoosac Tunnel. the Stampede Tunnel. and the Cascade Tunnel. The Hoosne Tunnel is on the line of the Fitchburg Railroad in Massachusetts, and passes through a southern extension of the Green Mountains known as the Hoosac Mountains. It is 48( miles long, and was driven from the two ends and from an intermediate shaft 1028 feet deep. Work was begun originally in 1855 and was car ried on intermittently, there being many long delays due to lack of funds and the obstacles en countered. The tunnel proper was completed in 1873, but several additional years were con sumed in the masonry work. The cost of the Iloosae Tunnel was about 811.000.000. The tun nel is 24 feet wide in the widest part. and 22 feet S inches high, and carries two lines of railway track. The Stampede Tunnel carries the Northern Pacific Railway through the Cascade Mountains, and was begun in 1886. From the time it was determined to make Puget Sound the western terminus of the Northern Pacific Railway, the question of a feasible route across the Cascade Range was prominently before the company. Between the years 1873 and 1884 several proposed routes were examined by the company's engineers, of which those via the Natchess, Stampede, and Snoqualmie passes were prominent. The Stampede route, lying between the other two, was finally recom mended, and was formally adopted by the com pany in 1884. Each of the routes named required a tunnel through the backbone of the Cascade Range; but the Stampede route was the longest of the three. The altitude of the mountain be neath which it was necessary to tunnel was 3970 feet above sea-level. and the greatest thickness over the top of t he tunnel is 1400 feet. the average depth being about 1200 feet. The elevation of the east portal of the tunnel above the sea is 2827 feet, and that of the west portal is 2800 feet. Work was begun in February, 1886. Probably no other tunnel was ever undertaken where the difficulties and cost of reaching the site and preparing for work were so great as at the Stampede Tunnel. The distance from the nearest railway to the cast portal was 82 miles. and to the west portal it was 87 miles, and all men, plant, and material had to he conveyed these distances on wagons and sleds. By the terms of the contract the size of the tunnel was feet wide and 22 feet high. The method of driving it was as follows: An 8 foot heading was driven along the top of the tun nel and was kept about 30 feet in advance of the bench where the tunnel was excavated to its full width. With the exception of about 500 feet in ward from each portal, where the rock was firm and stable, the entire tunnel was timbered as fast as the work progressed. The timbering made it necessary to enlarge the section called for by the contracts to a width of 19% feet and a height of 23 feet 10 in. The total length of the tunnel was 9850 feet, with a rising grade from each end to wa•d the middle. Power drills operated by com pressed air were used. The amount of explosive used was 309,625 pounds. The total cost of the tunnel was $1,160,000.
The Cascade Tunnel carries the Great Northern Railway through the summit of the Cascade Range in Washington. This tunnel is of particu lar interest because of the representative illus tration which it affords of modern rock-tunneling methods and machinery in the United States. The crossing of the summit proper of the Cascade Mountains since the construction of the Pacific extension of the Great Northern Railway in1891 92 was effected by means of a switchback. This switchback was built merely as a temporary line.
Business conditions, however, did not justify the construction of a tunnel between 1892 and 1897. hut in the latter year orders were given to com mence the work and push it as fast as possible to completion. The length of the tunnel is 13,813 feet, of which about 400 feet (or 200 feet at each end) is an extension of the permanent lining, to take the place of the wooden snow shed, but the length of the tunnel proper, from face to face of portals, is 2.61 miles. The width in the clear, inside of the permanent lining, is 16 feet, and the height from top of rail to bottom of arch is 21 feet 6 inches. For the first 500 feet at the west portal, the tunnel was driven through a slide com posed of gravel and large boulders. This ground was heavily impregnated with water, and the pressure from above was tremendous. The pres ence of the large boulders made it difficult to drive poling boards, and a hole a few inches in diameter, if left open, would soon let in sand enough to fill the heading. To earry this heavy ground required three concentric sets of timbers, as well as tie-rods, connecting the wall plates.
The ordinary Ameriean system of tunnel exca vation was employed. The overhead heading was taken out to the full size of the rock section, 10 X 20 feet. and the bench taken out in two lifts. Rock from the heading and top bench was wheeled in barrows out onto a large traveling carriage called a 'jumbo,' where it was dumped through chutes into the muck ears. Material from the lower bench was shoveled directly into the cars. On a secondary floor, under the main floor of the `jumbo.' was a hoist operated by compressed air, which was used to load large pieces of rock. some of them weighing six tons, on the flat ears. This obviated the necessity of bloekholing large pieces of rock, to enable them to be handled. This cable and hoist was also need to move the 'jumbo' hack from the rock face when blasting was to be done. Compressed air, at 100 pounds' pressure. operated drills, hoists, and pumps with the exception of one large pump which was operated by elec tricity. Four vertical columns in the heading cau•ried six 3%-inch Rand 'Slugger' drills. From 24 to 2S holes, 12 feet deep, were drilled in the breast, and fired by electricity, in three rounds. Holes were drilled to lift the top bench. and ver tical holes for the main or lower bench, enough to break the rock to subgrade. Altogether an average of fourteen 3%-inch drills were used in each heading and benches.
All hauling out of muck, and hauling in of con crete, was done with electric motors, of which eight were in service. Six of these were con structed at the tunnel machine shop. One of these motors hauled loaded trains of from 16 to 20 dump ears, of l cubic yard capacity, up the 1.7 per cent. grade, at 10 miles per hour. The foul air was exhausted from the heading through 2.1 inch galvanized iron pipe, by means of a No. 9 Sturtevant fan, running at 1700 revolutions.
The tunnel is permanently lined throughout its entire length with concrete, this lining being no where less than 23 inches thick, and in places feet thick. Where the section was larger than would admit of solid concrete, it was backfilled with spawls and broken stone, the result being a monolith of concrete from portal to portal. The tunnel excavation proper was commenced August 20, 1897, and completed October l3, 1900. The average monthly progress in the tunnel was 350 feet ; average daily progress 11.53 feet. The work of concrete lining the tunnel was commenced November 17, 1899, and completed November 17, 1900. The average monthly progress was 1115 feet.