Page:Popular Science Monthly Volume 89.djvu/566

 Ten Millions to Save Four Miles

��I.\ the t'anadian Rock\- iMmintaiiis is a giant mass of rork, towL-riin; f>,.S4 feet and known as Mount McDonald. It lies on the route of the Canadian Pacific Railway. Between Mount Mc- Donald on the right and Mount Tupper on the left, the road enters what is known as Rogers Pass. To reach the other side of the Rockies, the trains had to climb two long spiral loojjs. If they were to tunnel through the mountains the rt)ute v,uld he shortened only about four miles, but the grades would be reduced, with the result that much time would be sa\xxl as well as wear and tear 0:1 rolling stock. Besides, the expense and clanger of maintaining and operating four and one-half miles of snowsheds would also be eliminated. Considering lliese factors, as well as the amazing increase in traffic, an increase which involved double-tracking, it was decided to tunnel Mount McDonald.

Two years were spent by engineers in seeking the most favorable location for a bore. A spot was di.-.covcrcd best suited for an undertaking in ci\il en- [Jneering which coni])ans fa\-ral)ly \.ith the wonderful tunneling that has been done in the Swiss Alps.

The Selkirk Tunnel, as it has beca called, is of interest because of the unusual method employed in the boring. la all such work it is im[)ortant that (he excavated mati'rial shall be renioxed with the greatest facility; that the work uiukr way shall not he im[)eded; and thai pro- \ision shall he made for carrying high- jjressure air pipes for the drills, water ])ipes and ventilating suction |)ipes. And so it was decided to dig two tunnels — one of them a "pioneer tunnel," in engineering parlance, ilu- soli- function of which is to provide an outlet for the excaxatetl material.

If you will stud\' the pictures a |)pea ring on thene.vl pagi', ><ni will see at once how the pioneer tunnel fullils its pur|)ose. .'\t tin- east end llu' |)i(iiie(T tunnel was located fifty feet to the north of the center line of the main tunnel and .it the west end, lifix leet lo the Miiilli of i|. I'irst ol all, an upper center "heading" was dug. In other words, a rather shal-

��low channel was dug along the line of the main tunnel. After this center heading iiad been made, the work of digging out the main tunnel to its full dimensions proceeded. The material excavated was hauled to the pioneer tunnel, which runs parallel with the main tunnel, through cross-cuts, following the course shown by the arrows in the diagram Oil the following page.

After being con\eycd through the pioneer tunnel, it was carried back again to the main tunnel, but, of course, at a point far removed from the scene of operations. After that, it was hauled out on a trestle o\er standard-gage tracks through the main tunnel and dumped into regular railwa\- cars. The excavation was, of course, all done by steam sho\els of one and a half cubic capacity, which means that at a single scoop, a shovel would dig out about an ordinary wagonload of dirt and rock. The dirt cars were hauled to the mouth of the tunnel by standard-gage com- j>ressed-air locomot i\es.

The tunnel, which is fi\e miles long, lowers the summit of the line by fi\e hundred and fifty-two feet. Its esti- mated cost is over ten millicn tioUars.

The tunnel is twenty-nine feet wide and twenty-three feet high and follows a straight line under Mount McDonald, emerging in the Bea\'er Valle>- beNond at a point about one thousand feet below the i)resent railroad route.

The eastern end is directh- below Hermit, a station just east of Rogers Pass. The highest point reached in the tunnel is three thousand se\en luiniired and ninety-fi\-e feet below the summit of Mount McDonald peak. I'p to the in- tt'rior summit the passage through the tunnel has a grade of one per cent. The (limb for the tunnel is made b\- the rail- road on the most iiortlierK station on its route. 'The tunnel route originalK' disc-o\-ered h\- the engineers was six miles long, hut this was gradually decreased to conform to the five-mile tunnel. The jiass gi-ts its name from Major A. B. Rogers, who penetrated the faslnes.ses of the Si'lkirks in iSfti and discoxcred this opening through the range.

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