EXAMPLES OF PLAIN-CONORETE RETAINING WALLS.
Fig. 116 shows the standard plain concrete retaining wall of the New York Central and Hudson River Railroad.* This type is used for track elevation, and hence carries a train on the back-filling near the wall. The official drawing con tains the following notes. "1. The coping is to be made of 1 : 2 : 4 portland cement concrete, the body of the wall of 1 : 3 : 6, and the footing (the lower 4 ft.) of 1 :4 : 71. 2. The foundation is to be made to suit local conditions, but is never to be less than 4 ft. deep, unless good rock is found. Old railroad rails, 10 to 12 inches centers, are to be used when soft material is encountered. When piles are used in soft material, the outside pile under the toe is to be battered out 1 to 6. 3. Four-inch weep holes are to be left not more than 15 ft. apart, and are to have vertical blind drains running to the top of the wall. 4. The top of the coping is to slope inch to the rear. 5. All exposed corners and edges are to be rounded to 1-inch radius. 6. Expansion joints are to be provided 50 ft. apart by inserting one layer of tarred paper between the sections, the edges of the paper being kept inch from the face of the wall and the joint being marked on the face by a triangular groove inch deep made by nailing a strip on the inside of the form." Fig. 117 shows the forms used in constructing a consider able length of the wall shown in Fig. 116. The sheeting was 2-inch yellow pine laid with a ship-lap of inch and an open joint of inch. The form for the front of the wall was lined with thin sheet steel. The forms were made in panels 51 feet long, were shifted by a locomotive crane, and were removed after the concrete had set over night.
Fig. 118, page 528, shows the wall used by the Illinois Central Railroad on one side of its depressed line through Grant Park, formerly Lake Front Park, Chicago; and Fig.
119 shows the forms used in constructing the wall.f The wall was designed for an 8-foot surcharge. The concrete was laid in three courses, as shown by the dotted line in Fig. 119. The lower course was laid without joints, the second course had tongue and groove contraction joints every 108 ft., and the third course every 54 ft. A sheet of hydrex felt was inserted in the contraction joint to prevent adhesion between the two sections. The horizontal sections were
keyed by a tongue and grooved joint as shown in Fig. 119, page 529.
It is claimed that a wall stepped on the back, as shown in Fig. 119,
is more advantageous than one having a straight back, since with the former the lower part of the form can be more easily taken down and be moved ahead before the upper part can be removed. This advan tage is greatest in cool weather when the cement sets slowly.
Chicago and North Western Wall. Fig. 120, page 530, shows the forms and, incidentally, the dimensions of the wall employed by the Chicago and North Western Railroad in track elevation in Chicago and elsewhere.* A horizontal section 35 ft. long was built complete
from top to bottom in a day; and on account of the pressure due to
this height of wet concrete, frequent tie rods and strong bracing were required to keep the forms from spreading. The rods and bracing shown in Fig. 120 were entirely satisfactory. The 2-inch pipe were old boiler flues, and consequently cost but little more than the expense of cutting. The end of the pipe was 2 inches from the surface of the wall.
Compare Fig. 117, 119, and 120 as to the manner of building the forms to secure the off-sets on the back of the wall.