At most of the crossings, very little trouble was ex perienced; but at Center avenue, about one-half of the thirty-six holes were very bad. Most of these went down to a point about 60 feet below base of rail almost per fectly dry; but at about this depth, the water would break in in such volume as to drive the digger out until a siphon could be installed. These siphons were the ordi nary kind of steam siphon ; the only change being made was to put a tee on the intake, and into the tee to put pieces of 2-inch pipe about a foot long. These pipes were capped and drilled full of holes about % inch in diame ter, which prevented large gravel from fouling the siphon. The steam was furnished by two locomotives at a pressure of 140 pounds per square inch, and it took about all the steam a locomotive could furnish to run one siphon.
In concreting, the machine would be got ready with one batch in the mixer, one in the hopper car, and two in the hoppers, all of which could be dropped into the hole within about ten minutes ; then the siphon would be hitched onto the derrick line, and started. As soon as the water was down to within about three inches of the bottom, the concrete was dumped in while the der rick raised the siphon. The four batches would fill about 10 to 12 feet of the well, which generally stopped the flow. The hole was then filled by ehuting the concrete to it.
In one case, that of the south well in the center row of Center Avenue, the hole was finished; and, as it was not convenient to concrete at that time, was allowed to stand full of water for two or three weeks. When it was finally pumped out to be filled, it was found to have about four feet of clay, which had come down under the lagging. As this was removed, the flow of water increased, as well as the flow of clay from behind the lagging, until the hole became very dangerous to work in; so it was de cided that the only way to finish it was to dig another hole alongside this one, and use it as a dump. This was done, and it worked successfully. In the greatest number of cases, the concrete could be run in chutes directly into the wells ; but where this was not possible, a temporary track was laid along the center line of the row, and a hopper car used.
The mixture used was the same as for the abutments— that is, barrels of cement to a cubic yard of pit-run gravel.
Columns and The columns and cross girders erected during 1906 were of steel; but after the success attending the construction of slabs during that year, it was decided that reinforced concrete columns and cross-girders would not only be more permanent, but would be more economical as well, which was borne out as the following estimate will show (the estimate being for a 14-foot bent) : Steel column and cross-girder, 10,200 lbs., at 3.5
cents $357.00 Concrete column and cross-girder, 7.12 cubic yards, and bars at $20.00 142.40 The concrete construction thus costing about 40 per cent of the figure for steel work. This result was so surprisingly low that it was checked back by several men before being taken as correct.
The lengths of span of the cross-girders are 12 and 14 feet, these lengths being taken because of the fact that the shorter spans were more economical and their lengths worked out to fit the width of the right of way.
The columns are 24 inches square, reinforced by structural steel basket of four angles tied together with batten-plates about 2 feet C. to C. This basket was about 18 inches square, and was wrapped with triangular mesh of No. 12 gauge wire, the mesh being 4 inches, this giving a wrapped column. The unit load upon the columns was 807 pounds per square inch for the center column, and 545 pounds per square inch for the side columns, considering only that area inside the steel basket. Over the total area of column, this reduced to 454 pounds and 307 pounds respectively.
The work was done as follows: The concrete in the cylinders having been purposely left below grade, the frames or baskets were placed over the center of the well, carefully centered and plumbed, then enough concrete placed around the lower part to insure their being held firmly in place ; after this had set for two or three days, the column forms were set up and concreted up to the juncture with the cross-girders, which is at the springing line of the lower curve. These column forms were made in four pieces, metal-lined, and held together by girts, having a forked end to receive the bolt, this making a very stiff form.
The mixture used was a 1:2:4 concrete of screened gravel, torpedo sand, and cement, and was mixed and placed by hand.
The cross-girders are designed as simple beams of 14- and 12-ft. span, and are 2 ft. 6 in. wide, and 4 ft. deep at the center, the curve being put in for appearance only. They were designed as simple beams, for the rea son that they would be built as such spans, being bulk headed at the center line of columns at points most convenient.