Speeding Through Solid Rock
The Engineer’s Story of Mount Royal Tunnel where 1,000 Men Traveling 1,100 feet per Month Met on a Perfect Centre
S. P. BROWN
THE happiest moment in the building of a tunnel is that moment when the last shot has been fired, and the two headings meet.
There is thrill in that moment, even for the most practised tunnel-builder, because calculate and plan as we will, correct our lines and check our calculations as we may, we are, up to that moment, always obsessed with the idea that we may have gone wrong, and that our two headings, one coming and the other going, may fail to meet with the accuracy that we desire.
Such tilings do not often happen, it is true, but there is plenty of precedent for them, nevertheless. Perhaps the earliest recorded incident—there must have been many unrecorded ones, because tunnel building dates right back to the cave men of prehistoric times— happened about the year 152 A. D. At that time Nonius Datus, a Roman en-
gineer, was sent to Algeria to drive a tunnel for an aqueduct into Saldae. He carefully surveyed his lines and levels over the mountains, instructed the contractor how these were to be projected into the tunnel, and returned home.
Four years later he got a message from the Roman governor to come back to Algeria and explain why the headings did not meet.
Nonius Datus professed to find that the contractor liad committed “blunder upon blunder.”
The contractor indignantly denied the charge and said the fault was the engineer ’s.
“The usual excuse,” said Nonius Datus, or words to that effect.
It was the same old quarrel between the maker of plans and the one who carries them out that we are familiar with even in these days — the same old kind of quarrel that we order official probes into.
As far as my reading goes, the quarrel over the Saldaean tunnel was never satisfactorily settled. But this much we do know, that Nonius Datus solved the problem by connecting the two parallel tunnels by a cross drift, and the tunnel became an aqueduct.
What we would have done if the same kind of thing had happened in our tunnel under Mount Royal at Montreal, I won't pretend to say. You think, perhaps, that in these days, when our science is so scientific, and our instruments so perfect, that two tunnel head-
ings leading away from one another would be impossible.
Well, I don’t know. We had three sets of headings in this tunnel of just over three miles, and the greatest error in either of them was three-quarters of an inch in line and one-quarter of an inch in grade. Naturally, when the last heading was found to connect correctly, we lit up our cigars, looked wise, and began to make our plans for taking the first civic party to view the dim wonders of our hole through the mountain. For official purposes we treated this fortunate conjunction of our lines as a matter of course, but frankly we were as relieved and delighted as Dr. Koppe, the surveyor of the St. Gothard tunnel between Switzerland and Italy, must have been, when he found that the error in the junction of the headings in that tunnel, which is nine and a half miles long, was only eleven inches.
The popular idea is, I know, that nowadays we have instruments which indicate the direction of the headings so accurately that it is next to impossible to go wrong. This, however, is by no means the case. There is nothing automatic about tunnel surveying. Only by continuous measuring, and by the checking and re-checking of the lines b y independent observers, is it
possible to keep the headings going in the correct direction. You would be astonished at the .complex work involved in getting the right lines. In the case of the Mount Royal tunnel we had to locate and map all the topographic features in the immediate vicinity of the proposed line, and upon these maps decide the best position for the portals, shafts, and route of tunnel. This done, we had to make careful surface measurements in order to establish what is called the base line. We did this with tapes tested according to Government standard for tension and temperature, these tapes being kept during the work at a given strain, with thermometers to enable them to be corrected for temperature.
Having got in this way a very accurate “traverse,” the next thing was to sink shafts, and extend the base line down these shafts by means of plumb lines, consisting of heavy weights, suspended on piano wires, the weights being suspended in tubs of water and oil to prevent oscillation. From these lines the engineer’s lines were projected into the tunnel. The work was further complicated by the fact that the shafts had to be located on the company’s property, while the tunnel itself ran under property that did not belong to the company. However, we hit it right in each case, and while it would be true to say that we were surprised, it is true to say that we were very glad.
Having got our lines, and having obtained, by means of diamond drills, a pretty fair knowledge of the kind of rocks we had to bore through, all we had to do was to drive ahead, and keep at it. This work requires the most constant
supervision, owing to the changing character of the geological formation, and we had to be constantly prepared for surprises.
The more one sees of actual tunnel work, the more one winders at the success attained in it by the ancients. For instance, in a rock tunnel like that under Mount Royal, we are so dependent OD steam drills, high explosives and scientific instruments and tools, that the great tunnels built by the Greeks and Romans fill us with feelings of profound respect and admiration. History shows that long before the birth of Christ really enormous works of this kind were carried out. The Romans seem to have developed rock tunneling to an extraordinary degree. They early learned the use of fire and water to expedite their work. They built fires in their headings, and after the rock had become well heated, threw water or acid such as vinegar upon it, causing the rock to shatter and loosen. Slaves, prisoners and criminals were used on this work, as the death rate was extremely high. The gigantic character of some of these ancient works may be judged from the Lake Fucinus drainage tunnel mentioned by Pliny. This tunnel, built around A.D. 50, was one-third larger than the preliminary heading of the Mount Royal Tunnel, 400 feet deep, and three and a half miles long. It took eleven years to build, and 30,000 men were employed.
The Mount Royal tunnel, by contrast, is three and one-tenth miles long, and 22 feet high by 30 feet wide. Progress has been made in the headings, 9 feet high by 13 feet wide, at the average rate of 420 feet per month in each heading, giving a gross average of 1,100 feet per month, and a monthly maximum of 810 feet in one heading. One thousand men have been usually employed on the work, and 2,000 pounds of 60 per cent, dynamite has been used per day.
The method in this tunnel has been to drill 18 to 24 holes, 5 to 8 feet deep in the heading, put dynamite in them, fire the blasts electrically from the lighting circuit, get the loose rock down from the roof and sides by means of iron bars, then shovel the debris into cars and haul it away.
So we go on, day after day. We have to be prepared all the time to meet hard and soft rock, water, and other things. In Mount Royal there has been considerable variation in the character of the rock, and once we struck a considerable volume of water. This proved, as is often the case, to be a “pocket” of water in the mountain, which gradually drained itself away. The water in the tunnel furnished a fairly good flow at the time of the water famine in Montreal; we were thus able to give the city some small fire protection in the vicinity of our shafts, that we are very glad to say was not required.
One of the great secrets of successful tunnel building is the saving of labor. We always aim, for instance, to get the maximum of
assistance out of gravity. Thus in the Mount Royal tunnel we did not excavate to the full size of the tunnel, but drove headings of about nine by thirteen feet at the bottom of the tunnel. These headings were roofed in by “jumbo” timbers and in them tracks were laid for cars to take the “muck” away. The main body of excavation was above these headings, so that the loose rock could be shot down through openings into the cars beneath.
The rock is hauled out to crusher plants in the open, and after treatment there is sold for road-making, concrete work and so on—this again helping to offset the expense.
Although a tunnel through Mount Royal may seen a fairly straightforward piece of work, we have had some remarkable geological variations to deal with. For instance, at the city end, where there is much sand and clay, we have to use a steel roof shield, which eliminates the very heavy and expensive timberwork which would otherwise be necessary, as well as the chances of settlement and drainage in the ground above. This shield consists of a cutting edge, shaped to conform to the outline of the tunnel roof cross-section, which forms the front of a steel envelope extending over the platform on which the men work, and back far enough to lap over the last ring or section of the tunnel lining to be erected. It is forced forward into the earth by hydraulic jacks under a pressure of 5,000 pounds to the square inch. By this method the roof is never exposed, and the men are never endangered by falling material.
For the most part, however, on the mountain slopes the tunnel is through
good sound Trenton limestone, which was found in most places to be hard and crystalline and an excellent rock for tunneling. Occasionally we ran into large dykes of extremely hard rock, necessitating the use of two tempers of steel. On one occasion we ran into a difficult rock known as marmorized limestone. This marble was impregnated with quartz and a natural cementing material which made it hard to drill, and caused the muck to “set up” so rapidly that it was only with difficulty that it could be shoveled into the cars. In the mountain proper the roek is a very hard essexite, an igneous rock of an undoubtedly volcanic origin.
Gases Made Men Drunk
One of the most troublesome problems in connection with tunnel digging is the problem of ventilation. This is too complicated a subject to deal with in a popular way, but I may point out some curious problems which we were up against in this connection in the Mount Royal tunnel. The smoke from the blasts and the fumes from the gasoline engines and other gases had such an effect on the men that at times they became quite drunk. First we thought it must be the gasoline locomotives which affected the men. In the west heading we were using these locomotives right along, and it was only very occasionalv that any men were affected in that heading. But, curiously enough, at the Dorchester street heading under apparently similar conditions, we had a great many men temporarily knocked out. For the life of us we could not tell whether it was the gasoline locomotive or a combination of these products of combus-
tion with something else which caused the trouble.
We tried experiments to ascertain the reason, and had analyses made of the air, but the more we experimented the more confused we became. We took white mice into the tunnel, thinking we would solve the problem with them. But the remarkable fact was that when the locomotives were not working the white mice were knocked out, while the men seemed unaffected. On the other hand, when the locomotives were working the mice showed every sign of health, while the men were knocked out. Then again, a test on the bodies of mice that died showed no trace of carbon monoxide in the air. We eventually altered the gasoline locomotives over to electric locomotives and have had no more trouble.
Having given, in a rough, general way, an idea of some of the work of digging the Mount Royal tunnel, it will be interesting, perhaps, to deal with other types of tunnels.
Probably the greatest and most difficult piece of sub-aqueous tunnel work ever carried out by means of a pneumatic shield, were the four Pennsylvania Railroad tunnels under the East River in New York. In this work, which was carried out under the direction of Alfred Noble, the cover was very thin, and the material through which the tunnel had to be driven was largely quicksand.
In this work compressed air had to be used as a supporting medium.
“Air a supporting medium?” you say.
Yes, that and nothing else. Anybody, by the pressure of the ordinary atmos-
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Speeding Through Solid Rock
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pliere, ean keep the water in a tumbler upside down if he knows how. Most people have seen the trick done. On the same principle, when we are digging a hole through ground saturated with water, or through quicksand, which flows like water, we can keep either out by an equally opposing pressure. Invisible and all-pervading air is the medium by which you can apply that pressure all around. But once you have applied it, you dare not remove it until you have put something in the hole to take its
In the course of such work, an air lock is used to obtain access to the tunnel. This air lock is a steel chamber at the end of the shaft or tunnel leading to where the work is being done. When the air pressure in the lock is the same as in the tunnel we can open a door into the latter, and haul out the muck into the lock. Then we close the door and reduce the pressure in the lock down to atmosphere without reducing it in the least bit in the tunnel. A door opens at the other end of the lock, and out comes the load of muck to be emptied. As it goes back for another load the process is reversed.
Tunneling by compressed air is not all such straightforward work as this, however. Elaborate precautions have to be taken to see that exactly the right amount of air pressure is got and maintained. Too little pressure is as bad as none at all. Too much air may result in a blow-out. Another problem that was met with under the East River was due to the fact that the air pressure required at the top of the tunnel was different from that required at the bottom.
Apart from “blow-outs,” where the high pressure air escapes and permits water and flowing ground to rush into the tunnel, the greatest danger in subaqueous tunnel work is from the men locking out of the compressed air too fast and getting what is called the “bends.” If the men were to come straight out of the compressed air into atmospheric pressure it might kill them at once, and to come out in anything but the most leisurely way is apt to give them agonizing and often fatal cramps.
In this work the tunnel digger is dependent on the sand-hog. These men sometimes work under four atmospheres, and there they usually stop, for forty-five pounds gauge pressure to the square inch is about the limit of human endurance, although I believe 52 pounds has been used. In the tunnels under the East River the men worked in three-hour shifts under forty pounds pressure. Then they had to spend three-quarters of an hour in the air-lock while the pressure was slowly reduced to atmosphere. After a good rest they could repeat this just once, and then they were through for the day, when they could earn another $4.50 in the same manner.
Origin of Compressed Air System
Antedating compressed air in tunnel building under rivers was an ingenious plan devised by De la Haye in 1845. His idea was to dredge out a trench across the bed of a river, build a mat in this trench, and sink the tunnel tube on this foundation. This plan was successfully used in the Detroit River tunnels, completed in 1909. A later plan is the freezing process, as exploited by SooySmith. It has been experimented with a good deal in New York, but has not yet been found to be commercially practical.
Of course, digging the hole is by no means all in tunnel building. The lining of the tunnel, either by timber, rubble masonry, brickwork, concrete, or east iron, has next to be done. This is often very complicated and at times so closely associated with excavation as to be practically inseparable, as in the ease of shield work.
With the aid of improved methods and machinery, many wonderful triumphs in tunnel building have been achieved in recent years. In the case of the Mount Royal tunnel we have established a record for speed on this continent in driving a heading through solid rock. But when all is said and done, tunneling is slow and expensive work. When we consider the difficulties encountered and the comparative slowness of our progress, despite all the help modern science can give us, we cannot but admire afresh the daring and perseverance of the ancients, who conceived and accomplished such great works in the face of such overwhelming odds.
The Kaiser’s New Cafe at Potsdam
'T'HE Kaiser has lately added to his commercial activities by becoming the proprietor of a restaurant and cafe at Potsdam. Some time ago the municipality of Potsdam decided to close an old cafe situated beside the historical mill in front of the Sans Souci Castle. | The people of Potsdam complained to the Emperor that they had been deprived of their favorite cafe, and the Kaiser decided to build and equip at his own expense a restaurant on a site near the windmill. This restaurant has recently been opened. The Kaiser wrote to the lessee as follows:—
“Dear Herr Moritz.—You are to pay me the very low rent of $1,500 a year. Should my restaurant appeal to the Potsdamers and thrive commercially, I may increase the rent a little later on, so that I may make something out of it too. There is one condition to the lease. You must have the best coffee in Potsdam.”
The restaurant is doing well, and one of the most regular customers is the Kaiser himself, who always inquires how “my restaurant” is going.