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heat, of 42° C. or 107° F. in the body; much as 5° C. or go F. But, for the while the extreme practicable air tem- mean temperature throughout any conperature, still not free from the certain siderable length of the tunnel, the calcuprospect of impaired health and prema-lated result agrees exactly with actual ture death, would be that under which observation, however varied be the mountthe heat of the body should not rise ain profile overhead. In confirmation above 40° C. or 104°F. The latter limit the Author reproduces from the St. being applied to the atmospheric condi- Gothard Company's eighth report a Table tions affecting the two ends of the St. of observations made in 1578 through Gothard tunnel, the Author calculates 1,500 yards' length of the southern half that the practicable limit of air tempera- of the tunnel, between 5,000 and 6,500 ture should not exceed 45° C. or 114° F. yards in from the mouth. The variations in the Göschenen end, and 373° C. or of mountain profile may even have the 100° F. in the Airolo end, for the labor- effect of producing a practically uniform ers clearing the advanced headings. He temperature for miles of tunnel, notwithadds, in a tabular form, the corresponding standing hundreds of yards difference in figures for assumed cases both of harder the heights of rock overhead. For the and of easier work than that of removing temperatures to be expected at the midthe spoil from the ends of these particu. dle of the tunnel, the minuter calculations lar headings.
are given which had been made last year II.-Limit to Depth of Tunnel below by the Author, at the time when each Summit of Ridge. - The scale for increase end had been driven about 7,700 yards of temperature with depth, which obtains in, leaving then about 1,000 yards interin mines and bore holes sunk below level vening to be driven. His estimate, with ground, is inapplicable to mountains, a margin for error of + 2}° C. or 43° F. owing to the cooling effect of their ex- was 318° C. or 89° F. for the rock ; the posed sloping sides. From Borelli'e same for the air about 150 yards behind temperature observations in the southern either forebreast, prior to the two drivportion of Mont Cenis tunnel, Ansted ages holing through into each other; deduced an increase of 1° C. per 50 and 331° C. or 93° F. for the water issumeters, or 1° F. per 91 feet depth below ing from the rock. In March, 1880, after the summit of the mountain profile over the holing through, the actual mean temthe line of the tunnel; but that rate did perature of the rock for the middle not hold good for lower elevations in the length of 1,000 yards was found to be same profile, and was therefore not ap- 303. C. or 87° F.; and this was also the plicable as any guide for other tunnels. air temperature 150 yards behind the From his own observations in the St. forebreasts prior to holing through. At Gothard tunnel, from 1873 to 1877, for the two forebreasts themselves the air distances of 4,800 yards in from the temperature was brought down as low as northern mouth and 4,500 yards in from 278° C. or 82° F. while boring, and 30° the southern, the Author deduced em- C. or 86° F. while clearing away spoil : pirical formulæ for the temperature to be which was about 3° C. or 5° F. lower expected during the further, progress of than calculated, the reduction being due the work. These having been found to to an extra supply of compressed air hold good for the 2,000 to 3,000 yards during the last 1,000 yards' drivage. next driven, he now reproduces some of These several temperatures, though high the principal. For the temperature of enough to retard the progress materially the rock itself, the general average result in the middle of the tunnel, and render in its simplest form is an increase of 1° the work more laborious, was not so exC. per 48.4 meters, or 1° F. per 88.1 feet cessive as to entail either stoppage or of vertical depth below the surface of danger. the mountain. This scale gives too low General Remarks.—Having entered a temperature for parts of the tunnel minutely, and at great length, into the that are under valleys and plains on the various conditions affecting the execution mountain sides, and too high for parts of the work in the two ends of the St. under peaks; the variations from the ac- Gothard tunnel, the author refrains from tual temperatures noted at individual attempting to lay down a fixed limit, points in the tunnel amount to nearly as either of temperature or of depth, for
Vol. XXIV.-No. 143.
any future tunneling operations which ward, it would have been attended with may enjoy the advantage of resources several advantages, which he here resuperior to those hitherto available. But capitulates. It is not so easy from surthe means to be employed for dealing face indications to form an idea about with higher temperatures than have the quantity of water likely to be met hitherto been encountered would have to with, and the solidity of the rock to be be very carefully matured beforehand, driven through, as it is from the height both theoretically and practically. and contour of a mountain to calculate
Projected Simplon Tunnel.— The ex- the increase of temperature likely to be tent of guidance, furnished by the light encountered. The principles long estabof present experience, is illustrated by the lished by general mining experience may, author's application of his calculations to however, be properly applied to tunnelthe principal projects for tunnelling ing; and in the longitudinal sections through the Simplon. Of the longer compiled by the author for the St. Gothroutes plotted, for piercing the mountain ard tunnel, it is seen how the surface innearest its base, from near Brieg on the dications held good down to that depth: northern slope, those of MM. Favre & fissures, slides, and faults, noted on the Clo, and M. Lommel, each nearly 12 mountain profile, severally made their miles, would appear to be impracticable of appearance without fail in the tunnel, execution with the resources at present most of them in a very unwelcome manavailable. According to their mountain ner. A recent illustration from near the profiles, the depth of these tunnels below middle of the tunnel is cited. The author the ridge would be about 7,300 feet ; thinks it safer and easier to avoid difficulwhence the temperatures to be expected ties of this sort by careful selection of midway in the tunnels would be about route beforehand, than to try to get over 47° C. or 116° F. for the rock, and for them afterwards during the execution of the air 150 yards behind the forebreast, the work. For the projected Arlberg and about 53° C. or 127° F. for water tunnel in Austria, he is glad to find the issuing from the rock. In the shorter route laid down with a view to avoiding, and higher tunnel proposed by M. Stock- by a curved course, rock that seems likely alper, about 10 miles long, piercing the to let out streams of water.
Tunnels range at about 2,560 feet above sea-level through high mountains should, as far as and beneath a rather lower portion of possible, be driven in places where they the ridge, the author estimates the depth will have the least height and bulk of below the ridge at about 5,900 feet, and mountain overhead, and where they will the rock temperature midway in the tun- be likely to be most free of water. nel at about 40° C. or 104° F. ; here Mode of Driving.—The mode adopted therefore the extreme limit of practicable for driving the St. Gothard tunnel is not execution would be reached. In two considered by the author, from the exstill shorter and higher tunnels, each perience there gained, to be the most about 75 miles long, proposed by eligible for long tunnels, where not more MM. Clo & Venetz, and M. Jacquemin, than two ends can be driven, and these the temperature encountered would be not faster than a certain limit of speed, much the same as has been met with in and where it is impossible to foresee all the St. Gothard tunnel; but their greater the difficulties that may arise. In respect height above sea level would somewhat of the atmosphere pervading the working detract from the value of both these tun- places, that mode of driving seems indeed nels, as compared with those nearer the decidedly objectionable. In the St. foot of the mountain.
Gothard tunnel the long succession of Selection of Route.-Supposing its trenches and steps, by which the small height above sea level be already deter- advanced heading was gradually widened mined by commercial or political consid- and deepened to the full size of the finerations, the route selected for a tunnel ished tunnel, caused the working places should be such as to offer the greatest to stretch back as far as a couple of miles facilities for its execution. In the case behind the forebreast. Hence, even adof the St. Gothard tunnel, it was pointed mitting the practicability of artificially out by the author in 1877 that, if the supplying the advance heading itself with route had lain 1 mile or it miles west- | air so cold that, where the rock tempera
ture was from 40° to 50° C. or 100° to 120° from the forebrcast. As soon as the two F., the men could work a hundred yards headings met, a good current could be behind the forebreast, the author considers established right through from one end the same means would be altogether in- of the tunnel to the other, which would adequate for such a length as a couple be largely efficacious in keeping down of miles of tunnel, full of men at work the temperature at the working places, and smoke from blasting. Moreover, in during the subsequent enlargement of the usual plan of driving the advance the central length. heading along the crown of the tunnel, Haulage.- Manual or animal labor in the water issuing from the forebreast has the working places should as far as posto flow all along the heading, and then sible be replaced by mechanical power; down along all the following steps and though how to manage this practically trenches of the successive enlargements, for the most fatiguing portion of the before reaching the completed culvert in work—the clearing away of the spoilthe finished portion of the tunnel. The yet remains to be found out. Endlessauthor therefore suggests the desirability rope hauling, as already carried out at of proceeding by an inverted method, collieries, would be more convenient for somewhat as in metalliferous mines: removing the stuff than the use of comdriving the advanced heading along the pressed-air locomotives, the size of which very bottom of the tunnel, and carrying prevents their penetrating so far into the the culvert forwards promptly with it, so advancing end, and also interferes more that all water should drain at once into with the ventilation. a narrow channel, presenting small sur Artificial Cooling.–This is the most face for evaporation. Less moisture difficnlt question of all, and is by no would thereby be imparted to the air, means solved by the use of extensive apeven when driving through very wet pliances for supplying compressed air. rock, than is evolved in drier rock, from The heat from the rock is practically inthe vast extent of wet surface exposed exhaustible; and, whether all the airby the puddles and mud that are inevi- cocks at the forebreast are open, or all table with the ordinary mode of driving. shut, the air temperature 200 yards back Such an inverted method would doubt- is practically constant and equal to that less present difficulties in regard to ven- of the rock, and thenceforth gradually tilation; but more attention might ad- rises as the air travels further back along vantageously be paid in tunneling to the the working places. The utmost cooling improvements that have already been at the forebreast, while four rock-drills realised in mine ventilation by the adop. are working together and discharging tion of systematic arrangements.
For their exhaust air at 21 to 4 atmospheres long tunnels that will take years to exe- pressure, does not exceed 42 C. or 7° F. cute, instead of improvising foul-air out- at most, the average being only 1° C. or lets temporarily and at random, or open. 2° F. below the rock temperature; and ing cocks here and there on the com- during the clearing away of the spoil the pressed-air main, a regular system of air may rise as high as 4° C. or 70 F. ventilation should be carried out by above the rock temperature, the average means of brattices, air-doors and trunks, being 17° C. or 3° F. above. A table is and should be pushed forward continu- given of periodical observations made by ously to follow up the progress of the the author at both ends of the St. Goth
A further suggestion for facil- ard tunnel while the drivage was susitating the execution of tunnels through pended for surveying the line of driving, hot rock is to complete each end to the the working places being then deserted full size as far in from the mouth as can and the air cocks left open. These rebe done without the heat becoming too cords show that with a rock temperature oppressive, say up to 30° C. or 86° F.; of 47° C. or 116° F. it would be no easy and then to push forward and complete matter to keep the air down to 35° C. or the advance heading alone, without con- 95° F. in the working places while work tinuing the work of enlarging behind it. was being carried on. There is no great The practical difficulty would then be difficulty in delivering highly compressed reduced to the efficient ventilation of the air in large quantities at the forebreast; heading for a length of 100 yards back the difficulty lies in arranging its distri.
bution. Men cannot work within a dis- with skill and perseverance, form as valtance of 5 or 6 yards in front of an uable a class of workmen for European aperture not more than 4 inches diameter; tunnels as the Indians of Mexico or South and often put a basket over it to break America for tunneling operations in the blast. The most serious obstacle to those countries. Under such circumthe use of compressed air, as the sole stances as obtained in the St. Gothard means of cooling, lies in the low specific tunnel, the author considers that, having heat of air, whereby vast volumes become regard both to economy and to health, heated immediately to the temperature the average duration of shift should not of the rock, without perceptibly cooling exceed eight hours. Two hours must be the rock itself. A jet of cold water has allowed for walking in to the working very little cooling effect on the air, and places, when at a distance of 4 to 41 the mist thereby produced is decidedly miles in from the mouth; then some rest objectionable; on the contrary, indeed, is needed before commencing work; and the compressed air should itself be sup- two to three hours' work is all that can plied as dry as possible. To cool the air be managed before starting on the two before delivering it into the tunnel is of hours' return journey, which should also little use, because its cooling effect de- be made leisurely on foot. The men at pends much more on its sudden expan- the boring machines, and those clearing sion; and also because, however cold it away spoil just behind, having the coolest may have been at the tunnel mouth, by and driest air, often remained fourteen the time it reaches the inner end of a hours in the St. Gothard tunnel. The very long main, the air is found to have men should strip themselves of clothing acquired within 2° to 3° C. or 4° to 5° F. as far as possible, so long as the air temas high a temperature as the surrounding perature is lower than that of the body; atmosphere in the tunnel
. As a means if ever tunneling came to be done at a of cooling in combination with other higher temperature, it would of course plans, the adoption of compressed air be desirable to work with clothes on. points to the use of compressing appara- Wherever artificial cooling of the air is tus on a much larger scale than that at required, the working places should also either Mont Cenis or St. Gothard. A be followed up closely by suitable refuges further problem will be to devise better or chambers, fresh and well ventilated, methods for drying the air. The air re- and even filled with dry air at a slight servoirs at Mont Cenis and St. Gothard excess of pressure, where any one overanswered the purpose to a certain extent, come with exhaustion can be promptly and were supplemented by additional restored, and where the men can dry and appliances at St. Gothard. For com- change before leaving work. Cooling pletely drying the air, Professor Dubois- beverages are recommended, for avoiding Reymond's suggestion to employ quick- the danger of drinking too much cold lime might be adopted; and the author water while at work. points out that this mode of drying In conclusion the author points out would be more efficaciously applied to that, from the nature of the work in long the compressed air before its delivery tunnels under high mountains and through into the tunnel, than by conveying the hot rock, the question of cost, and even lime itself to the working places. The of time, may often become a consideracooling mixture of ice and salt should, tion of secondary importance. however, be conveyed in the spoil-wagons to the working places, and there dis Height OF WAVES.–From the result charged on the off side; as it gradually of ten thousand observations, it appears melted away, the water would run off, that the cubes of the heights are proporbut without imparting so much moisture tional to the squares of the velocities of to the air as if there were no salt mixed the winds. A wave of 2.20 meters in with it. The combination of these two height corresponds, according to the plans appears to the author to offer the author, with a wind of 5 meters per best means of enabling tunnels to be second velocity; and as the relation driven at high temperatures.
(2.20m)'=x (5)', :: x=0.426, and conseWorkmen and Shifts. - Italians, used quently (2 H)=0.426 v». Hence 2 II, to a warm climate, and taking to mining the total height of the wave,=0.75 vk.
AN ADAPTATION OF BESSEMER PLANT TO THE BASIC
By A. L. HOLLEY, Memb. Inst. C. E., &c.
From Papers of the American Society of Mechanical Engineers. The maintenance of refractory linings Basic bottoms and tuyeres stand ten in Bessemer converters, in such a way as to fifteen charges, nearly equaling acid to promote regular and maximum pro- bottoms, and they may be readily changed; duction, has been the subject of more but basic linings, near the tuyeres, and experimenting than any other feature of also in other parts where abrasion is the Bessemer system, and it is still the severe, wear rapidly and must be freleast perfect and satisfactory feature, ex- quently repaired by cooling the convertcepting perhaps the casting of steel. er and inserting new bricks, or patching Linings are not only eroded by the me- in some suitable manner. The converter chanical action of the charge, but they is thus put out of use for at least twentyare chemically decomposed by its various four hours-a very serious delay to proslags. The silica linings usually employed duction. From a wide observation the have, indeed, been so improved, that an author feels safe in saying that a basic average of say 60 charges per 24 hours lining is rarely run above 60 charges can be got out of a pair of converters, without extensive repairs, and in some and the shifting of interchangeable con- works repairs are made every time a botverter bottoms (containing the tuyeres) tom is set. With some irons there is also is so rapid that it does not delay produc- an accumulation of slag around the tion; but the repairing of the fixed lining mouth of the converter; its removal just above the tuyeres, where both me- sometimes also causes delay. chanical and chemical action are most The output of a pair of converters in severe, is frequently the cause of delay, Europe averages about half that of a pair and the operation rapidly performed be- of converters of the same size in the tween heats is tedious and costly. The United States, and is often less than half. accumulations of slag on other parts of The limited endurance of basic linings in the lining must also be quarried out, else Europe is therefore a less conspicuous the converter will become too small for defect than it is here, where one conthe charge.
verter must make 25 or 30 charges in 24 These are the conditions of maintaining hours, so that the repairs of basic linings, silica linings; but the difficulties are in- as at present conducted, would keep an creased, probably about threefold, when American plant idle about half the time. the linings are made of lime, for the basic This delay is really as important in Euprocess. The basic process consists in rope as it is here; the greater the output removing phosphorus from the iron un from a given plant, the cheaper the proder treatment, by retaining the phos- duct.* In order, therefore, that the basic phorus oxidized by the blast, in a basic process may come into extensive use, slag formed of say 20 per cent. of lime basic linings must be so maintained that added to the charge. An acid (silica) their output will nearly equal that of acid lining would vitiate the basic slag, and linings. would also be rapidly destroyed by it. There are two reasonable conditions Lime containing some magnesia, and of improvement; the one is to prolong produced by burning magnesian limestone the endurance of basic materials, so that (dolomite), is at present the only basic their repairs can be made with little dematerial successfully used for converter linings. It is usually made into bricks, rapid production in America impairs quality of product, which are hard-burned and built up with is but a cover for inadequate plant Steel is obviously mortar of similar material to form the in setting a vessel boitom, or because it may take twice lining
* The statement sometimes made in England that the
as long in an English works to handle materials and product.