Plan of Section 15.

rate of speed but carrying buckets spaced proportional to the required ingredients. Stone was conveyed from the spoil bank to the crusher by wheelbarrowmen. Cement and sand were hauled

by teams and dumped directly into the mixer bins.

Fig. 527 shows a similar sketch of the work on Section 15. The quarry is within the Main Channel limits and about 1,000 feet from the No. 7 Gates crusher, on to the tipping platform of which the loaded cars were drawn by a cable hoist. The average output of the crusher for a day of 10 hours was about 210 cubic yards. The transportation of materials to the mixer was effected by a standard gauge light locomotive and Petla dump cars of about four and one-half cubic yards capacity water measure. The mixer consisted essentially of a spiral screw rotating in a trough, mixing and depositing the ingredients on a rubber belt conveyor running over concave pulleys. The water was applied by a spray pipe as the mixer discharged the material upon the conveyor. The mixer was operated by an engine and boiler mounted upon a separate car. The entire apparatus was moved along its track by means of a block and tackle operated by a winch on the engine.

Fig. 528 shows the crusher on Section 15 and the quarry in the background, at the left of which is a section of finished wall.

Supports for the concrete forms were made by setting vertical posts about nine inches in front of the face of the

wall and eight feet apart; an iron dowel pin set three or four inches into the rock held the foot of the post in place;

TABLE IV.

CONCRETE RETAINING WALLS, SECTION 15.
Itemized Table of Force, Percentages and Cost.

Typical Rates per day Percen

Co-t

of 10 hours

tage of

per

cu. yd.

each.

Cost.

(Cents.

wooden braces held the posts in place longitudinally and tie rods. connected them with a line of similar posts at the back of the wall. The forms were sixteen feet long and two feet wide, dressed on one side; they were set as the work advanced, and were held in line by wedges.

Two one-foot courses of concrete were laid, and after an interval of about twenty-four hours the forms were drawn, cleaned, and set for the succeeding courses. A loose link passed around the post and through a block supporting the bottom of the form and acting as a friction clutch. The Portland cement facing was placed by using plates of iron held by blocks three inches from the forms; as the course was completed this plate was withdrawn and the union between the mortar and concrete thoroughly tamped.

The combination of one part of screenings with two parts of sand could be used as sand.

In tables III and IV the typical force is based upon a superintendent as a unit. The total force does not include machinery. Rates for machinery cover the cost of coal, oil, and waste only. The estimated values of the plant makes no allowance for salvage. The installation and wrecking of plant, delays caused by strikes or lack of material, insurance on property or persons, storage, repairs, interest on investment, etc., are not included in cost prices. Utica cement is rated at 65c per bbl.; Portland, at $2.25, and sand at $1.35 per cubic yard.

The contract prices per cubic yard on Section 14 were: Excavation, 38c; concrete masonry, $2.74; backfilling, 14c; and on Section 15 the concrete masonry was $3.40.

The total yardage involved on Section 14 was 23,568, and on Section 15, 44,811. The average daily output of the two types of machines was practically the same, being about 100 cubic yards per day of ten hours each. The concrete was composed of two parts of cement to three of sand to eight of broken stone; the Portland mortar was a one to three mixture. The structure is a monolithic mass; no attempt was made to predetermine vertical cracks.

The inspecting force for each section on both masonry and concrete work consisted generally of a head inspector in charge, a warehouseman, and as many inspectors on mortar and wall as the plants operated by the contractors required.

The assistant engineers in charge of the work were Mr. Hiram A. Miller, to October, 1895, and Mr. Chas. L. Harrison, to August, 1897.

DISCUSSION.

By L. K. SHERMAN, Mem. W. S. E.

Mr. Beardsley's paper furnishes valuable data on the relative cost of concrete and rubble masonry. Rubble masonry is shown