Although, on account of the soft nature of the ground along the right of way, all of the walls rest upon piles, no cracks have occurred. Of the maximum section, 24 ft. high, there is a total length of 1,700 ft.; and of this length, 1,000 ft. is in one continuous wall.
The following specifications for materials for reinforced concrete retaining walls are those given by one of the largest manufacturers of reinforcing material in the United States: Specifications for Materials for Reinforced Concrete Retaining Walls Cement. Only Portland cement conforming to the requirements of the specifications adopted by the Amer ican Society for Testing Materials, June 14, 1904, shall be used.
Sand. Sand to be clean and coarse, and free from organic matter; a graded sand, with coarse grains pre dominating, is to be preferred.
Coarse Aggregate. Broken stone to be bard, durable limestone, or its equivalent, free from dust and foreign materials; maximum-sized particles to pass through a one-inch ring; fines to be removed by passing over a one-quarter-inch screen. The fines may replace part of the sand. Under special conditions making for uniform ity, crusher run may be used, but this is not desirable.
Gravel shall be clean and of graded sizes; the sand carried to be removed by screening as for broken stone.
Proportions of Mix. Concrete for wall, base, and buttresses to be mixed in the proportion of one part cement to six parts aggregate; proportions by volume, taking one bag containing not less than 94 pounds of cement, equal to one cubic foot of cement.
The proportions of fine and coarse aggregate used shall be chosen so as to give a concrete of maximum density; in no case, however, may the amount of fine aggregate be less than 50 per cent of the coarse.
Reinforcing Steel. All reinforcing steel used in re taining wall construction shall be rolled to such form that it has a positive mechanical bond with the concrete. Adhesive bond will not be considered sufficiently reliable for this class of structures.
Steel may be made by either the Bessemer or open hearth process; bars to be rolled from billet stock. Re rolled material will be accepted under conditions insuring rigid inspection.
The elastic limit and percentage of elongation shall be determined by tests on accurately-machined speci mens, and shall conform to the following requirements: Elastic limit to be from 50,000 to 60,000 pounds per square inch, ultimate strength not less than 1i x elastic limit.
The percentage of elongation in 8 inches must not be less than given by the formula : 1,400,000 Percentage of elongation= 5.
Ultimate Strength Bending Test. Bars as rolled shall bend cold, 90 de grees, to a radius equal to three times the least diameter of the specimen, without sign of fracture.