CENTRAL SHAFT.
[The Plate, opposite page 74], conveys an idea of the sinking of the Central Shaft at 891 feet depth; at the time of writing, May, 1872, however, this shaft had not only reached grade, but to a sump beneath grade at a depth of 1,040 feet; headings and enlargements have been also driven at grade, east and west, to meet the works from the East End, and from the Western Shaft. Owing to the stratification of the rock, which dips towards the west, great progress was anticipated in this direction; but man proposes and God disposes; on reaching about 300 feet westward, seams of water were struck, of so threatening a nature that a powerful Cornish pump was erected, at a cost reaching, in all its details, $80,000, and now, May, after enlarging the diameter of the former plunger pump, prudence suggests the temporary delay of any further disturbance of this water inlet (immediately under the divide of the mountain), until the present pumping force has sufficiently drained the sources of water supply to permit a further advance of this (the western) heading of the Central Shaft to be driven without involving a flooding out of the men working at the eastern heading. Meanwhile, from the sump, the excavations are enlarged to full tunnel size, the capacity of the Cornish and plunger pumps are being tested, and all energy summoned to meet any difficulties to be overcome when this western heading of the Central Shaft shall resume work. All the rock here has to be moved from the heading by hand power, and lifted (by steam power) 1,000 feet to the surface, yet, notwithstanding these adverse circumstances, during March, 100 feet was driven to the eastward alone. I append a memorandum furnished by Mr. E. A. Bond, of actual drilling and blasting, taken at this point during the dates given, being about the average performance.
On August 19th, 1871, on the north side of the east heading, machine No. 1, starting at 10 a. m., had at 2.08 p. m. drilled three holes, averaging about five feet four inches; the time actually occupied in drilling being 74 minutes, or an average of about 25 minutes to each hole. The remaining 2 hours and 54 minutes are accounted for by changes of drills, breaking of carriage, and an interval of 40 minutes for dinner. On the south side, machine No. 2, starting at 9.35 a. m., had at 2.09 p. m. drilled three holes, averaging about six feet four inches; the time actually occupied in drilling being 81 minutes, or an average of 27 minutes to each hole. The remaining 3 hours and 13 minutes are accounted for in a similar manner to the time of machine No. 1, except that there was no accident to the carriage. The average time of the two machines was about 26 minutes for the average depth of about five feet ten inches, being two inches and seven-tenths per minute. It will be seen by these facts that the actual drilling is but a comparatively small part of the work; bringing forward the machines, connecting to the air main, inserting the drills into the jaws of the machine piston, changing these drills as they wear down, oiling, releasing drill when stuck, removing back the machine carriage out of reach of the blasted rock, waiting for blaster to charge the holes, connect his wires, and apply the electric current to fire the exploders, removing the debris to clear the track for the approach of the drills—all these operations, so varied and yet so necessary, each consume a considerable quota of the eight hours allotted to each shift.
On August 30, 1871, a blast was made in the east heading at 5.30 p. m., as follows: fourteen 7 foot holes were fired with 25 lbs. of Nitro-Glycerin, throwing out about 30 tons of loose rock; and one solid rock, diameter 9 × 4½ × 4 feet, and weighing about 24,000 lbs., a distance of 30 feet, a weighty testimonial to the explosive power of Nitro-Glycerin.
The expense incurred and difficulties met with, in working at the Central Shaft, will serve as a hint to contractors to make all due allowance in their estimates for striking a seam of water; work may go on smoothly for a long time; the general geological formation of hill or mountain may be well understood, and yet the contractor cannot tell but that he may strike a vein of quartz that may throw him back days and weeks in his drilling calculations, or a seam of water which will cost him thousands of dollars in machinery and labor to keep it under.
On December 7, 1870, the hoisting machinery broke at the Central Shaft, and then the following measurements of water were made. On December 3, the depth was 3 feet; December 13, 7 feet; December 15, 8½ feet; December 20, 21 1/6 feet; and December 24, 48½ feet. At midnight they commenced bailing with two buckets, one having a capacity of 341 gallons or 54.65 cubic feet, and the other 189½ gallons or 31.36 cubic feet. The large bucket was hoisted 1,075 times, bailing 58,745.3 cubic feet of water, and the small bucket 966 times, with 29,327.8 cubic feet of water, the whole amount being 549,179.0 gallons in 27 days, or 21,080.0 gallons per day.
The following anecdote is worth relating, as showing the wonderful escapes men sometimes have, when the chances are one hundred thousand to one against their lives:
In February, 1872, Thomas Hawkins felt tired and sleepy, and concluded to lie down in the east heading of the Central Shaft, about 30 feet distant from where the blaster was charging sixteen holes with Nitro-Glycerin, intending to retire when the holes were charged. But he failed, as we many of us do, to carry out his intention. When the blaster had charged his holes, he left the heading, connected his wires, and having halloed the usual warning “Fire,” and every thing being quiet, discharged his blast. Thomas Hawkins was awakened by the report of the blast, scattering 30 or 40 tons of rock, and annoyed to find his foot bruised, he limped out to meet the miners returning to their work, who now, when a blast is about to take place, unceasingly ask him where he proposes to take up his position, that they may choose an equally safe place.
An escape, as wonderful, at the West Shaft, is worthy of being recorded. On August 3, 1868, as Richard Dunn was advancing to the heading, with a can about a quarter filled with Nitro-Glycerin, his foot slipped, and, in trying to avoid falling, he swung the can over his head, striking the drilling machine frame, and fell prostrate, still holding the can; a rush of air was heard, and the can was found as shown in the [photograph, page 66], the Nitro-Glycerin not having exploded. The man got up a great deal more unconcerned than those at work near him, and quietly went forward and filled his cartridges as if nothing had happened. As I told him afterwards, he will never be so near eternity again without actually reaching it. The can had been filled at a temperature of 45°F, and the temperature of the room where it had been stored for 36 hours, was about 65°, thus causing an expansion both of the Nitro-Glycerin and the air contained in the can.
The West End of the Tunnel comprises the brick arch and portal, well No. 4, the supplementary shaft, and what is known as the West Shaft. The brick arch has been driven through what is aptly termed, “demoralized rock,” for immediately after the spring thaw it becomes a quicksand, and spews into the tunnel from every direction. By driving small adits on each side, and a central adit some distance ahead of the main tunnel, Mr. B. H. Farren overcame this dangerous and difficult work, which at one time threatened his contract, and thus enabled the arch work to be carried on. Subsequently, the central adit was carried through to the West Shaft, and thus the costly and difficult task of lifting 420 gallons of water per minute, to a height of 320 feet, was avoided, and it now escapes by natural flow through the west portal. Drilling is practised here as described for the East End and Central Shaft; in the East End the heading is driven on grade, and the overhanging enlargement is “stoped” out by hand drilling worked from an arched stage, ([see plate opposite page 85]) thus avoiding the necessity of handling twice; mules draw the laden trucks, from the heading and beyond where this stopeing out of the roof is going on, to the locomotive, which hauls a train of cars laden with stone to the dump.
At the West End, however, the roof of the heading is driven in line with the roof of the tunnel, which is hereby left complete as the heading progresses; this involves trucking by hand, and dumping the rock from the heading over the bench to the lower level, [see plate opposite page 90], and is not found so economical as the East End method. These differing methods of working, however, were not started simply as experiments, but for good engineering reasons; at the East End, the dump was ample below the grade of the outlet, whereas, at the West End there was no opportunity to get out at the portal, on the line of the intended railroad; all the rock here had to be lifted (until the portal and arched work were completed) up and out of the West Shaft, and dumped on to the mountain side, and, to avoid being impeded by water, the heading was driven on a level higher than the grade of the Tunnel, thus ensuring good drainage for the most important part of the work, as it was then deemed, viz.: monthly linear advance. For the Commissioners were servants of the public, and the advance, rather than the enlargement of the Tunnel, was the measure of their success so far as public opinion was concerned.
Only by a personal visit to this enormous work can a correct idea be obtained of the expense, ingenuity, engineering skill, and indomitable energy of the several foremen and superintendents at the four divisions, viz.: East End, under Mr. Blue; at the Central Shaft, under Mr. Roskrow; at the West Shaft, Mr. Williams, with underground superintendent, Mr. White; and at the West Portal or arch work, the sub-contractors, Messrs. Hocking and Holbrook; all of whom are daily devising more expeditious methods of detail, in compassing the great end sought by each brigade, the completion of the Hoosac Tunnel contract at the time specified.
And whilst this energy, this organization, and all this development of the highest grade of modern engineering, are being devoted to carrying out the expressed wish of the majority of the people of Massachusetts, the malcontent minority is sleepless in offering every possible obstruction to the work; in Governor’s council, in consulting engineering supervision, in committee of assembly, in the newspaper press, covert expression of the opposition has found vent, and been doubtless useful in its way. But is it not time this opposition should cease? Must our citizens be for ever confined to one route from their Capitol to the West? Surely there will be traffic enough and ample, to remunerate both lines, when the Hoosac Tunnel route is open. If so, the time is approaching for a generous welcome from the opponents of the Hoosac Tunnel, and the conditions “at owner’s risk and at corporation’s convenience” may cease to appear on our freight notes.
Driving Bench Work and Dumping from Heading
(West End.)
Instructions for Handling and Using
MOWBRAY’S
TRI-NITRO-GLYCERIN.
1. Handle carefully, avoiding a sudden jar or concussion, and be very careful, if any is spilt outside the can, to avoid striking it against any hard substance.
2. When solid, thaw out by placing the cans in a tub of warm water, not hotter than the wrist can bear, first pouring warm water into the can, and always remove the can before adding more hot water to the tub.
3. To fill Cartridges, &c.—Hold the Cartridges to be filled over a tray, say 2 feet by 3 feet, the bottom of which should be covered with Plaster of Paris (which will not readily explode when saturated with Nitro-Glycerin.) The soiled Plaster of Paris should be frequently renewed.
4. If the Nitro-Glycerin in a liquid state is kept in store or magazine for some time, the cork should be loosely inserted, and a pint of cold water poured in each can, to be frequently poured off and replaced with fresh cold water in warm weather, taking care to retain the bladder under the cork. It is preferable, when ice can be procured, to congeal the Nitro-Glycerin.
5. Use Funnels (gutta-percha if they can be had) for filling water holes. Under no circumstances whatever attempt to tamp the drill holes; it is unnecessary, and may kill the man who attempts it.
6. Hot irons to warm the water, or soldering the cans, will be sure to cause explosions.
7. Never sledge or attempt drilling in a hole or seam where Nitro-Glycerin has been spilled; fire an exploder, which will effectually clear it up.
8. Never pour Nitro-Glycerin into a hole unless perfectly sure that it is a sound hole, or will hold water; if seamy always use cartridges.
9. To obtain the best results with Nitro-Glycerin, drill deep holes, 6 feet or more. Use powerful exploders and well insulated wires. It is cheaper to fire by electric battery with simultaneous explosion, than to fire several holes with tape fuse.
10. Look out after a blast for any unexploded cartridges lying around.
11. Never allow any but the most careful persons to handle or have charge of the Nitro-Glycerin, and insist upon the use of every precaution to prevent an accident or explosion.
12. Never allow empty Glycerin cans to be used for any other purpose, but destroy them by a fuse and exploder, or building a fire under them, first, however, removing them to a safe distance.
13. Examine your cans from time to time, and notice if, at the level of the Nitro-Glycerin, any pin-holes have eaten through; in such case procure a new can, or stone jar, and empty the contents out, not trusting your hold to the upper part of the can, lest it may give way.
14. When solid, or congealed, it is absolutely safe; if possible, therefore, any surplus should be stored surrounded with ice, since no explosion can take place when it is solid.
George M. Mowbray.
North Adams, Mass., June, 1872.