With the advent of gunpowder and canal con struction the first strong impetus was given to tunnel-building in its modern sense as a commer cial and public utilitarian construction. Canal tunnels of notable size were excavated in France and England during the last half of the seven teenth century. These were all rock or hard ground tunnels. Indeed, previous to 1800 the soft-ground tunnel was beyond the courage of the engineer except in sections of such small size as hardly to deserve the name of tunnels. In 1S03, however, a tunnel of 24 feet wide was excavated through soft soil for the Saint-AumFtine Canal in France. Timbering was employed to support the walls and roof as fast as the earth was re moved and the masonry lining was built closely following it. From the experience gained in this tunnel were developed the Various systems of soft-ground subterranean tunneling since em ployed. It was through the development of the steam railway, however, that the art of tunneling was to be brought into its present prominence. In 1820-26 two tunnels were built on the Liverpool and Manchester Railway in England. This was the beginning of the rapid development which has made the tunnel one of the most familiar of engineering structures. The first railway tunnel in the United States was built on the Allegheny Portage Railroad in Pennsylvania. in 1831-33; and the first canal tunnel had been completed thirteen years previously (1818-21) by the Schuylkill Navigation Company, near Altoona, Pa.
The art of tunneling entered its last and great est phase with the construction of the Mont Celli; Tunnel in Europe and the lIonsay Tunnel in -America. The Mont Penis Tunnel was undertaken to facilitate railway communication between Italy and France, or, more properly, Piedmont and Savoy. the two parts of the kingdom of Vic
tor Emmanuel Tl. separated by the Alps. It is 7.0 miles long and passes under the Col de near Mont Penis. \Vork was begun in 1857 and finished in 1870. It was from the close study of some of the diflieulties, the great length of the tunnel, and the desire of the engineers to finish it quickly, that all the different improvements were developed which marked this work as a notable step in the advance of the art of tunnel ing. Thus the first power drill ever used in tun nel work was devised by Sommeiller, one of the engineers. In addition compressed air as a mo tive power for drills, aspirators to suck the foul air from the excavation, air compressors, tur bines, etc., found at Mont Cenis their first appli cation to tunnel construetion. This important role played by the Mont Cenis Tunnel in Europe in in troducing modern methods had its counterpart in America in the Hoosac Tunnel, completed in 1375. In this work there were used for the first time in America power roek-drills, air compressors, ni troglycerin, electricity for firing blasts, etc. There remains now to be noted only the final de velopment in the art of soft-ground submarine tunneling, namely, the use of shield and metal lining. The shield was invented and first used by Sir Mare I sambard Brunel in excavating the first tunnel under the River Thames at London, which was begun in 1325 and opened in 1843. In 1869 Peter William Barlow used an iron lining in con nection with a shield in driving the second tun nel under the Thames at London. From these inventions has grown up one of the most notable systems in tunneling now practiced, known as the shield system.