The Bridgeport evening farmer., 1913-09-06

A very disturbed formation existed at this point, layers of sound rock alter. ma ting with Assures of highly distn- tegrated rock, the latter resembling
 greensh sand.
 THE TROUBLE ZONF.
 The zone of trouble as it is desig mated by the engineers was in fact made LID of a complex structure of rock. White limestone and gneiss were the chief constituents and seams Of pure tale, 2 inches thick, iron pyrites, mica, seams of pure asbestos one-quar- ter inch thick, tourmalfne, semi-pre- cious stone, calcite crystals, tremoI1te chrysta1s, cIays ranging from gray to red snowdrop marble and limestone of various other co1ors shading from gray to white and dykes of granite and seams of rotten rock were among the other substances passed through in me
 entire length of the tunnel The chief trouble, however, arose from the con tacts of beds, of limestone and gneiss- This contact results in the decomposi- ton of both, but chiefly limestone, and as a result much of the material through which the engineers had to work was disintegrated mud and soft crumbling rock. Added to this, the forma ton gave evidence of volcanic action. A large number of steanas or disintegrated rock bearing water un- der full head were found and also I ably been previously washed out.
 Owing to the great depth of the tun- ne1 the use of compressed air s an and to fight the incoming water, as Is common in tunnels of shallow depth, was impossible, as it would have re- quired some 11O pound pressure per square inch above the normal to hold the water, whereas 40 pound pressure per square inch above normal is con- sidered quite high for men to work in. Therefore great care was exercised in driving the tunnel through this belt Before advancing the heading, in every instance thorough exploration of the rock in advance was made by drilling test holes of a greater depth than the customary drill-holes. When water was encountered it was allowed to run | and carry with it the sand in the hs-
 sures penetrated, and thus create | void into which ''grout,' a mixture of cement and water, could be forced un- | der great pressure, and thus fill them with the grout which, when set, form ed solid plug There was occasions
 also where, after advancing the head ing, a steam would break away and allow the water to come in. To cope | with this it was necessary to construct
 a wall of concrete to reinforce the rock in which were placed suitable pipes for the water to come through until free of any suspended material and then in turn be used to inject the grout So great was the flow at times 1 that one single leak gave 5000 gallons | Of water per minute, and as high as | 4,80O gallons of water per minute for a period of A hours has been pumped. | The area of the Assures can also be
 gagged from the fact that as high 1 1,Oo0 barrels of cement has been forced
 under a pressure of 800 pound per square inch into a single Assure.
 | Sometimes water under full pressure would be struck so that it would shoot
 the drill back out of the hole. In such | eases it was necessary to drive pipes | in these holes and wedge them into
 the rock to make them water-tignt.
 At times it took eight or ten men work 1 ing together and often Wading up to 1 their knees in icy wat.r, 10 force the pipes against the flow of water. Grout pipes were then attached and grout was forced up to 800 pounds which when set made that part of the seam solid. When no more water could be located the heading was advanced un- til water was again found. During one ] Of the floods connection with the river l was direct that hundreds of live fish came through. These were taken home by the workment and eaten. An other incident showing the -directness
 of the connection with the river of the
 rock material is furnished in the fact
 that while grouting during the last l flood connection with the river was | got by means of bubbles-through 90
 feet of water and 125 feet of rock.
 The work involved the exercise of l extreme caution and was consequently l tedious and slow, one could not l foretelI what was ahead On one oc-
 casion in the Bronx heading, where | the grade was descending from the
 shaft making the face the lower of 1 the two, the influx occurred without
 warning, flooding the tunnel to a depth of six feet at the face making it nec-
 essary for the men to use improvised