If we could keep the rock-drills running all the time, and eliminate all the other operations except as they could be carried on without interfering with the drilling, that would certainly seem to promise more rapid progress. This is the idea which the inventors of the tunneling-machines are working on, and it is no wonder that there are a great many struggling to develop something practical along this line. At the same time it must be said that there is not in use at the present time a commercially successful tunneling-machine.

The idea is misleading. With the drilling-and-blasting system, the drills cut considerably less than 1 per cent, of the material; the tunneling-machine proposes to cut up practically all the material into chips, or to do more than a hundred times as much mechanical cutting of the rock with the time multiplied only by three or four, and no allowances for machine- or drill-arrangements or other time-losses.

Were nitro-glycerine and dynamite undiscovered, the tunneling-machine would be of great importance. It would seem fundamental that, in counting the cost, it is more economical to dislodge rock from its strong place in a tunnel-heading by discharging a high explosive at the bottom of a hole than by doing all of this work through the pulverization of the entire mass, especially so as the material removed may be of large or small size, the main point being to get it out of the way. An argument used by the advocates of tunneling-machines is that the chief problem in driving is to get rid of the material. There is a good deal of truth in this when applied to tunnels of large diameter and to headings where the material is discharged en masse at the face and in large and irregular pieces. The Alpine system reduces the importance of the problem of getting rid of the material, for the reasons that have been stated.

A tunneling-machine which attempts to bore a hole 2, 3, or 4 ft. in diameter is a reasonable proposition, but the difficulties are usually increased out of all proportion as the diameter of the tunnel is enlarged. It is not uncommon to put in holes with a large rock-drill, using bits 6, 8, and even 12 in. in diameter. This might be extended to several feet by increasing the diameter of the drill in proportion as the size of the bit is enlarged. The most reasonable of the numerous tunneling-machines that have been suggested is that known as the Karns, described later on, which is nothing more or less than a rock-drill with a large bit. Its limitations are mainly in connection with large diameters and because of the irregular nature of the rock, causing it to strike harder on one portion of the bit than on the other, and the effect of this is, of course, more destructive as the diameter is enlarged.

Radialax System of Tunnel Driving

A heading-driving system, known as the Radialax, which has been used in coal-mines, and to a limited extent in tunnels, is that in which a single channel is cut in the face of the heading. This channel may be from 2 to 4 in. in width, and preferably 4 or 5 ft. deep. Having such a cut, preferably in the center of the heading, the problem of removing the surrounding rock becomes a simple one, because the heading is now nothing more than a double bench, and we know that the amount of explosive required in bench-work is considerably less than in headings, hence a minimum of explosive is used and the shock of blasting is considerably reduced. This system has special advantages when driving tunnels under foundations of buildings and through places where the noise and shock from blasting are destructive or objectionable.

Fig. 9 shows the Radialax machine cutting a channel in the face of a tunnel-heading. This machine consists of a modified form of rock-drill mounted upon an arm which is, in turn, mounted upon a column. A common X-bit is used, and, while it is being reciprocated by the drill, the operator, by means of a worm and quadrant, swings the bit radially, thus cutting a vertical channel. Owing to this radial movement the channel cut is longer at the bottom than at the face of the rock. The channel need not reach from roof to floor in order to be effective as a center release-line towards which the side-round blasts are directed.

The tunneling-machines here mentioned are only typical of a great number. H. A. Everest, in a graduating-thesis at the Colorado School of Mines last year, gave a record, beginning in 1853, and mentioning about 30 different machines. The brief descriptions of three or four machines here given are partly abstracted from that paper. The inventors of these machines recognize the most urgent problem of tunnel-driving: how to advance the heading more rapidly. That none of them will achieve a practical solution which may ultimately materially lower the time-record for tunneling in hard rock it is perhaps unsafe to predict.

Proctor Tunneling Machine

This machine is the joint production of O. S. Proctor, of Denver, and E. F. Terry, of Terry & Tench Co., contractors, New York. This is to cut a tunnel or heading 8 ft. in diameter, converting all the material into dust or chips. There is a four-wheel truck at the rear which travels on a track, and the front end is carried by two conical wheels, which fit the circle of the tunnel on each side and thus keep the head central. The main shaft, which is hollow, has adjusting-screws at the back by which the direction of advance may be controlled either vertically or horizontally. In the middle of the track is a rack by which the machine is fed along and constantly held up to the work. This feed is by means of an air-engine and worm-gearing on the truck. Another air-engine with another train of gearing slowly rotates the head. This head has a hub, a casing, four connecting-arms, and four bars which carry pneumatic hammers with chisel bits. Upon three of the bars six hammers are mounted, and upon the fourth bar there are seven, and as the head rotates they cut along different overlapping circles and thus cover the entire face of the excavation. Steel plates fixed between the groups of hammers are arranged to form pockets to catch and carry away the rock chips. These discharge into a hopper at the rear of the rotating head, and a conveyor leads to the rear of the machine. The designers estimate that this machine will be capable of removing 5,000 cu. ft. of rock per day, which would be equivalent to an advance of 100 ft., and, of course, three or four times as fast as by the drilling-and- blasting method. It is also calculated that $300 per day will be sufficient to meet all the expenses involved in operating the machine.

The Karns Machine

This machine, the invention of J. P. Karns, formerly of Cripple Creek, may be called an enormous percussion-drill reciprocating a single cutter-head. The first machine tried in the Cripple Creek district used a column to support it. The company has at Magnolia, Colo., a 6-ft. machine mounted on a carriage. The head is 4 ft. in diameter, and is attached to a 9-in. shaft, which extends about 10 ft. to the back of the carriage, where it has a spherical direct connection with the 4-in. piston-rod of the actuating cylinder. The head rests on a cylindrical shield, which in turn bears on small wheels. The shield carries 3-in. balls on which the head rolls, and these balls rest on eighty 5/8-in. balls. There is much more of complicated description which we cannot profitably follow. The cutters are made of bars 1 in. thick, 4 in. high, and of lengths varying from 9 to 24 in. Their faces are serrated so that there are a number of square pyramids on each. The cutters are arranged in three sets, the outer set having 24 cutters of medium length, the next set having 17, one being left out so that a man can get through the head, and the center set having 4 short cutters in advance of the others, which help to keep the machine in its path. An endless scraper, 27 ft. long, driven by a small three-cylinder engine, is provided to remove the cuttings, but it is expected that they can be flushed out by water.

This machine has actually done some work. A short run was made a year ago; The engine used was too large to follow in the bore of the 6-ft. cutter, and the compressors were too small to maintain more than one-half the pressure desired. The machine was run 6 min. 30 sec. for an advance of 2 in. The rock was a fairly-hard syenite, composed almost entirely of feldspar.

The Sigafoos Machine

This machine, invented by R. B. Sigafoos, of Helena, Mont., is an electrically-driven machine, and the entire machine rotates upon wheels, which may be given a helical pitch to advance or withdraw the machine by its own rotation and to feed it slowly against the rock when in operation. The work is done by crushing or pulverizing the rock and washing it out with water under pressure. The rotating frame carries 10 crushing-heads, each mounted on a 4-in. shaft. These are withdrawn by cam action, and a long, heavy helical spring shoots the shaft and crushing-head forward, the several heads striking in succession. The frame is made up of two heads connected by a 6-inch central rod and eight 1.5-in. tie-rods near the outside. The length over all is about 18 ft., and the weight is 20 tons; the weight is considered sufficient to hold it up to its work. Eight of the cutters are on the outer edge of the machine and two are near the center. The heads are about 2 ft. in diameter and about 5 in. thick. The teeth are not sharp and do not require sharpening. The cuttings are to be flushed out by a 3-in. stream of water under 40 lb. pressure, fed through the central shaft, and a spray-head keeps a 5/8-in. stream behind each cutter. A 150-h.p. electric motor will be used, it being assumed that 65 h.p. will be required to start the machine, while half of that will be enough to keep it going.

The Fowler Machine

The machine of George A. Fowler is one of the latest which has come to the knowledge of the public, and its scheme of operation is different from that of any of the others. It is expected to cut a rectangular face 7 ft. by 6 ft. 6 in., using 38 percussion-drills, all operating at once and all being moved about to cover the entire area while in rapid operation. The drills are arranged as a battery upon a massive cast-steel head hung by heavy hinges from the front of the machine. This head is to move back and forth to cover the entire face three times a minute, the drills striking at speeds up to 1,000 per minute. The movement of the head is not absolutely automatic, but can be controlled by the operator according to the requirements of the rock. There is no rotation of the bits, and the drills are not quite parallel, flaring enough at the outside to provide for necessary clearance and the maintenance of the full areas as the work progresses. The cutting-battery is framed in a shield which tits the periphery of the tunnel all around, inclosing all cuttings, which collect at the bottom, where they can be carried backward on to an elevating conveyor by the collective exhaust of all the drills and delivered to cars in the rear. The valve-motions of the drills and other details of this machine are novel and interesting, but we need not consider them here.

The Bennett Machine

This machine, the invention of G. R. Bennett, of Denver, it is rather more difficult to take seriously than even some of the others. It carries 48 hammer-drills with 4-in. bits, drilling horizontally to a depth of 2 ft., then withdrawing and resetting laterally and again vertically until eight successive sets of holes have been drilled, thus covering a rectangular area of 8 ft. by 5 ft. 4 in. with 384 holes, all the shiftings and resettings being done automatically. The drills are set eight in a row horizontally with 8-in. centers, and they are spaced vertically with 4-in. centers in two sets of three each with 12 in. between the sets. The drive is electric, each vertical set or battery of six having one feed-cylinder and one driving-pinion, the sets striking alternately. The sets of drills are fed forward 2 ft.; as each set finishes its cut it is drawn back and the power is automatically shut off, and when all eight of the sets have thus finished their cuts the machine shifts over 4 in., and another cut is started. When this cut is done the drills are all dropped together 1 ft. and the previous drilling-operations are repeated. This finishes the upper half of the face; the drill-carriers now drop 3 ft., and a repetition of all the previous operations completes the entire face. It is thought that the webs of rock remaining between the holes will break down of themselves, but if they should remain until the series of holes are all drilled a man can go in and quickly break them down. It is not assumed that any of this breaking away could interfere with the constant automatic action of the drills and shifting-devices.