[1] There are two important secondary techniques for opening subterranean and subaqueous ways, neither a method truly of tunneling. One of these, of ancient origin, used mainly in the construction of shallow subways and utility ways, is the “cut and cover” system, whereby an open trench is excavated and then roofed over. The result is, in effect, a tunnel. The concept of the other method was propounded in the early 19th century but only used practically in recent years. This is the “trench” method, a sort of subaqueous equivalent of cut and cover. A trench is dredged in the bed of a body of water, into which prefabricated sections of large diameter tube are lowered, in a continuous line. The joints are then sealed by divers, the trench is backfilled over the tube, the ends are brought up to dryland portals, the water is pumped out, and a subterranean passage results. The Chesapeake Bay Bridge Tunnel (1960-1964) is a recent major work of this character.
[2] In 1952 a successful machine was developed on this plan, with hardened rollers on a revolving cutting head for disintegrating the rock. The idea is basically sound, possessing advantages in certain situations over conventional drilling and blasting systems.
[3] In 1807 the noted Cornish engineer Trevithick commenced a small timbered drift beneath the Thames, 5 feet by 3 feet, as an exploratory passage for a larger vehicular tunnel. Due to the small frontal area, he was able to successfully probe about 1000 feet, but the river then broke in and halted the work. Mine tunnels had also reached beneath the Irish Sea and various rivers in the coal regions of Newcastle, but these were so far below the surface as to be in perfectly solid ground and can hardly be considered subaqueous workings.
[4] Unlike the Brunel tunnel, this was driven from both ends simultaneously, the total overall progress thus being 3 feet per shift rather than 18 inches. A top speed of 9 feet per day could be advanced by each shield under ideal conditions.
[5] Ideally, the pressure of air within the work area of a pneumatically driven tunnel should just balance the hydrostatic head of the water without, which is a function of its total height above the opening. If the air pressure is not high enough, water will, of course, enter, and if very low, there is danger of complete collapse of the unsupported ground areas. If too high, the air pressure will overcome that due to the water and the air will force its way out through the ground, through increasingly larger openings, until it all rushes out suddenly in a “blowout.” The pressurized atmosphere gone, the water then is able to pour in through the same opening, flooding the workings.
Agricola, Georgius, [215],[216]
Barlow, Peter W., [221], [227]
Beach, Alfred Ely, [224], [227]-[229], [231], [237]
Brunel, Marc Isambard (the elder), [204], [205], [217], [218], [221], [224], [229], [231], [236]
Burleigh, Charles, [212], [213]
Burleigh Rock Drill Company, [212]
Burr, S. D. V., [236]
Cochrane, Sir Thomas, [231], [232]
Copperthwaite, William Charles, [224]
Doane, Thomas, [210], [212], [213], [215]
Drinker, Henry S., [224], [237]
Greathead, James Henry, [204], [218], [221], [224], [229], [231], [235]-[237]
Gwynn, Stuart, [210]
Haskin, DeWitt C., [204], [232], [234]-[236]
Haupt, Herman, [204], [209], [210]
Hobson, Joseph, [237]
Latrobe, Benjamin H., [208], [209]
Law, Henry, [218]
Mowbray, George W., [213], [215]
Nobel, Alfred B., [213]
Putnam Machine Works, [212]
Shanley, Walter, [212]
Shanley Bros., [215]
Sommeiller, Germain, [210]
Storrow, Charles S., [210]
Tweed, William Marcy (Boss), [229]
Weale, John, [218]
Transcriber’s Notes
All obvious typographical errors corrected. Formatting inconsistancies and spelling were standardized. Paragraphs split by illustrations were rejoined. The [a]Index] was extracted from the full publication Index.