The age-herald., 1901-05-05
TUNNELlNG IN CITIES.
Some Problem of Underground Rail.
 way Construction.


 From the New York Mail and Express In comparison with the underground railway systems of the old world, notably
 those of London and Paris, the rapid transit subway in which New Workers ex- pect to take their first ride on Christmas day. 1903, presents engineering problems
 which simple and straightforward.
 The advantage which the work here have
 over the work abroad is due chiefly to the
 plan on which the city of New York was
 laid out.
 AS the new subway is to follow and go under broad business and residence
 streets. running for miles without break north and south, 1t will be what engineers
 call. by contradiction in terms, sur
 face" subway. In Paris and London the
 underground railways dive deep below
 the level of the street. Because of the
 maze of thoroughfares in London and
 the broad boulevards in Paris, radiating
 like the spolxes of a wheel from com
 mon center, the engineers of any system
 which is designed to give quick service to
 the public and a profit to its promoters
 have to draw plans for tn construction
 of their broad road which will allow for
 the support of heavy buildings.
 In this city engineering problems of this
 kind have not come up for solution. Ac- cording to the present plans-and there Is no reason for believing that they will be
 altered-the subway will have to support
 buildings at probably only four, and at the most only five. points on the line.
 At the curve from Park avenue Into For ty-second street the tracks will run diag-
 onally across and under the southwest corner. At Fourth avenue and Eighth street they will take a short cut under property on which a row of old-fashion- ed brick buildings Is now standing. How
 ever. 1t Is likely that before the work
 reaches that point the buildings will
 have been torn down. At three other places sharp curves are planned which will carry the road partly under build ings
 Each building under which a tunnel has to go must be considered as separate
 problem. At Forty-second street the
 method will be simple, the ordinary sys-
 tenn of needles and shores" being em- ployed. Needles are pieces of timber. 10
 or 13 inches square, and of any desired length, which are placed in a horizontal position from to 10 feet apart under
 heath and perpendicular to the wall of the building. Under each needle are placed two posts, the one outside the wall
 and the other inside. All that remains to be done Is to set the 1aborers to dig
 ging. sheet up the ground with 2-inch blanks, put in braces and carry the walls
 on the needles until the permanent sub
 
 If the contemplated tunnel to Brooklyn
 becomes a. certainty 1t will be a more difficult piece of work than any now un- | der way along the subway route because | 1t will have to go down to bedrock below | the caissons on which a modern office | building rests. In a case of this sort, the | buildings will be supported by the solid | rock through which the tunnel Is being l bored. re-enforced by a complicated sys- | tenn of great timber arches. An example | of this kind of tunneling Is afforded at the Park avenue section of the subway where Contractor Ira Shaler Is driving
 tunnels simultaneously from Thirty
 fourth street and Forty-second street to
 meet in the center. At the lower end he
 has penetrated 250 feet to Thirty-fifth street The work here has been compar- atively simple, because the rock itself Is strong enough to support the car tracks. the wall of the old tunnel and the street traffic above. At the upper end. however. the soil Is of different character. and timberwork Is necessary. On the west side of Park avenue, below and in front of the Murray Hill Hotel. a larger arch with a spen 30 feet Is be- ing used to carry the tremendous weight of wall, car track and street travel It Is possible to go under anything by em- ploying system of timbering. If con tractor Is willing to work slowly and spend sufficient sum of money.
 The new Paris underground railroad.
 the Chemin d'Orleans. runs directly un-
 der a five-story office building, which was occupied while the work of construction
 was in progress. The Chemin d'Orleans.
 by the way. Is not a steel structure. but masonry tunnel. By complicated system of needles, shores and girders. the. building mentioned was literally pinned up while the engineers were taking the wall of masonry under it. In London. the ''tu-penny tubes" run underneath a large number of buildings, but far below the
 there are. so to speak, three layers of
 underground railroad
 By act of Parliament the railroads more
 recently built have been forced to keep
 to the clay stratum which is from 50 to 70 feet below the surface. Clay is the safest kind of soil to work in. Construc- ton may be carried on without danger to buildings. and the clay itself. although tough and hard. may be cut like cheese. No more roads like the Metropolitan are to be permitted in the British capital. The
 Metropolitan Is comparatively close to the street level. When 1t was being carried under the Bank of England. the con- tractor was obliged to use compressed air to equalize the pressure.
 The dangers of tunneling under build ings are not as great as might be sup posed. There is little likelihood of a cave in If the building were undermined, the walls would settle or crack and every one above and below would have time to get out In perfect safety In Chicago the set