Filling Forms of Lower Face Walls.—­A temporary trestle was erected above the elevation of the bridge seat, and a track, leading from the mixer to the form to be filled, was laid on it.  At the commencement of each section a layer of mortar (1 part of cement to 2-1/2 parts of sand) was deposited on the bottom.  A 1:3:6 mixture of concrete was used; it was run from the mixer into dump-cars and deposited in the form through chutes, three of which were provided for each 50-ft. section, the average length.  The concrete was mixed wet, and was not rammed; the stone was spaded back from the face, and no facing mixture or facing diaphragms were used.  Work on each section was continued day and night without any intermission from the time of commencement to the time of completion.  At frequent intervals the box drains were washed out thoroughly with a hose, in order to prevent them from clogging up with grout.

[Illustration:  PLATE LI, FIG. 1.—­TW 66, P.N.Y. & L.I.R.R.  Terminal Station West.  Box drains and tie rods, South side, Sta. 184+80 to 185+14.  Sept. 17, 08.]

[Illustration:  PLATE LI, FIG. 2.]

[Illustration:  PLATE LI, FIG. 3.—­P 46.  P.R.R.  Tunnels, N.R.  Div.  Sect.  Gy.  West.  Disposal trestle just before demolition.  View of South side showing chutes.  Jan. 21, 09.]

[Illustration:  PLATE LI, FIG. 4.—­A 54.  P.R.R.  Tunnels, N.R.  Div.  Sect.  Gy.  West & Oj.  View across North River on line of Tunnels, looking from New York to New Jersey.  Feb. 9, 07.]

In the first few sections of wall, the form was filled to within 1 in. of the top of the bridge seat and allowed to set for about 2 hours; it was then finished to the proper elevation with a plaster of 1 part of cement to 1 part of sand.  This did not prove satisfactory, as there were indications of checking and cracking, and, later, the form was filled to the required elevation and the surface floated.  The form was allowed to remain in place for from 18 to 24 hours, depending on the weather.  In most cases, immediately after the form had been moved, a scaffold was erected against the face of the wall, and the face was wet and thoroughly rubbed, first with a wooden float and then with a cement brick, until the surface was smooth and uniform.

The section 1 ft. square at the top of the bridge seat, which was left out in order to brace the bottom of the form for the upper face wall, was filled in after the walls had been completed.  The old concrete was very thoroughly cleaned before the new concrete was placed on it, and a gutter was formed at the rear connecting with the box drains back of the wall to carry off rain-water coming down the face of the upper walls.

In hot weather the walls were thoroughly wetted down several times a day for several days after the form had been removed.