Chapter VIII.

~WALLS IN TRENCH.~--In canal excavation, in subway work in cities, and the like, it is often necessary to dig trenches and build retaining walls in them before excavating the core of earth between the walls. The following examples of such work are taken from personal records:

Example I.--A Smith mixer was used, the concrete being delivered where wanted by a Lambert cableway of 400 ft. span. The broken stone and sand were delivered near the work in hopper-bottom cars which were dumped through a trestle onto a plank floor. Men loaded the material into one-horse dump carts which hauled it 900 ft. to the mixer platform. This platform was 24×24 ft. square, and 5 ft. high, with a planked approach 40 ft. long and contained 7,300 ft. B. M. The stone and sand were dumped at the mouth of the mixer and shoveled in by 4 men. Eight men, working in pairs, loaded the broken stone into the carts, and 2 men loaded the sand. Each cart was loaded with about 70 shovelfuls of stone on top of which 35 shovelfuls of sand were thrown. It took 3 to 5 minutes to load on the stone and 1 minute to load the sand. The carts traveled very slowly, about 150 ft. a minute--in fact, all the men on the job, including the cart drivers, were slow. After mixing, the concrete was dumped into iron buckets holding 14 cu. ft. water measure, making about ½ cu. yd. in a batch. The buckets were hooked on to the cableway and conveyed where wanted in the wall. Steam for running the mixer was taken from the same boiler that supplied the cableway engine. The average output of this plant was 100 cu. yds. of concrete per 10-hour day, although on many days the output was 125 cu. yds., or 250 batches. The cost of mixing and placing was as follows, on a basis of 100 cu. yds. per day:

Per day. Per cu. yd.

8 men loading stone into carts $12.00 $ .12 2 men loading sand into carts 3.00 .03 1 cart hauling cement 3.00 .03 8 carts hauling stone and sand 24.00 .24 4 men loading mixer 6.00 .06 1 man dumping mixer 1.50 .01 2 men handling buckets at mixer 3.00 .03 6 men dumping buckets and ramming 9.00 .09 12 men making forms at $2.50 30.00 .30 1 cable engineman 3.00 .03 1 fireman 2.00 .02 1 foreman 6.00 .06 1 waterboy 1.00 .01 1 ton coal for cableway and mixer 4.00 .04 ------- ----- Total $107.50 $1.07

In addition to this cost of $1.07 per cu. yd. there was the cost of moving the whole plant for every 350 ft. of wall. This required 2 days, at a cost of $100, and as there were about 1,000 cu. yds. of concrete in 350 ft. of wall 16 ft. high, the cost of moving the plant was 10 cts. per cu. yd. of concrete, bringing the total cost of mixing and placing up to $1.17 per cu. yd. As above stated, the whole gang was slow.

The labor cost of making the forms was high, for such simple and heavy work, costing $10 per M. of lumber placed each day. The forms were 2-in. sheeting plank held by 4×6-in. upright studs 2½ ft. apart, which were braced against the sides of the trench. The face of the forms was dressed lumber and all cracks were carefully puttied and sandpapered.

The above costs relate only to the massive part of the wall and not the cost of putting in the facing mortar, which was excessively high. The face mortar was 2 ins. thick, and about 3½ cu. yds. of it were placed each day with a force of 8 men! Two of these men mixed the mortar, 2 men wheeled it in barrows to the wall, 2 men lowered it in buckets, and 2 men put it in place on the face of the wall. If we distribute this labor cost on the face mortar over the 100 cu. yds. of concrete laid each day, we have another 12 cts. per cu. yd.; but a better way is to regard this work as a separate item, and estimate it as square feet of facing work. In that case these 8 men did 500 sq. ft. of facing work per day at a cost of nearly 2½ cts. per sq. ft. for labor.

Example II.--The building of a wall similar to the one just described was done by another gang as follows: The stone and sand were delivered in flat cars provided with side boards. In a stone car 5 men were kept busy shoveling stone into iron dump buckets having a capacity of 20 cu. ft. water measure. Each bucket was filled about two-thirds full of stone, then it was picked up by a derrick and swung over to the next car which contained sand, where two men filled the remaining third of the bucket with sand. The bucket was then lifted and swung by the derrick over to the platform of the mixer where it was dumped and its contents shoveled by four men into the mixer, cement being added by these men. The mixer was dumped by two men, loading iron buckets holding about ½ cu. yd. of concrete each, which was the size of each batch. A second derrick picked up the concrete bucket and swung it over to a platform where it was dumped by one man; then ten men loaded the concrete into wheelbarrows and wheeled it along a runway to the wall. One man assisted each barrow in dumping into a hopper on the top of a sheet-iron pipe which delivered the concrete. The two derricks were stiff-leg derricks with 40-ft. booms, provided with bull-wheels, and operated by double cylinder (7×10-in.) engines of 18-HP. each. About 1 ton of coal was burned daily under the boiler supplying steam to these two hoisting engines. The output of this plant was 200 batches or 100 cu. yds. of concrete per 10-hr. day, when materials were promptly supplied by the railroad; but delays in delivering cars ran the average output down to 80 cu. yds. per day.

On the basis of 100 cu. yds. daily output, the cost of mixing and placing the concrete was as follows:

Per day. Per cu. yd. 5 men loading stone $ 7.50 $.07½ 2 men loading sand 3.00 .03 4 men charging mixer 6.00 .06 2 men loading concrete into buckets 3.00 .03 1 man dumping concrete from buckets .50 .01½ 10 men loading and wheeling concrete .00 .15 1 man dumping wheelbarrows 1.50 .01½ 3 men spreading and ramming 4.50 .04½ 2 enginemen 5.00 .05 1 fireman 2.00 .02 1 waterboy 1.00 .01 1 foreman 6.00 .06 10 men making forms 25.00 .25 1 ton coal 4.00 .04 Total 85.00 $.85

In addition there were 8 men engaged in mixing and placing the 2-in. facing of mortar as stated above.

~CHICAGO DRAINAGE CANAL.~--The method and cost of constructing some 20,000 ft. of concrete wall by contract in building the Chicago Drainage Canal is compiled from records kept by Mr. James W. Beardsley. The work was done on two separate sections, Section 14 and Section 15. In both cases a 1-1½-4 natural cement concrete was used with a 3-in. facing and a 3-in. coping of 1-3 Portland cement mortar.

Section 14.--The average height of the wall was 10 ft., and the thickness at base was one-half the height. The stone for the concrete was obtained from the spoil bank of the canal, loaded into wheelbarrows and wheeled about 100 ft. to the crusher; some was hauled in wagons. An Austin jaw crusher was used, and it discharged the stone into bins from which it was fed into a Sooysmith mixer. The crusher and the mixer were mounted on a flat car. Bucket elevators were used to raise the stone, sand and cement from their bins to the mixer; the buckets were made of such size as to give the proper proportions of ingredients, as they all traveled at the same speed. Only two laborers were required to look after the elevators. The sand and cement were hauled by teams and dumped into the receiving bins. There were 23,568 cu. yds. on Section 14 and the cost was as follows:

Typical Wages per Cost per General force: force. 10 hrs. cu. yd. Superintendent 1.0 $5.00 $0.026 Blacksmith 1.1 2.75 0.016 Timekeeper 0.5 2.50 0.007 Watchman 0.6 2.00 0.007 Waterboys 3.9 1.00 0.022

Wall force: Foreman 0.9 2.50 0.013 Laborers 8.6 1.50 0.073 Tampers 2.3 1.75 0.022

Mixer force: Foreman 1.2 2.50 0.017 Enginemen 1.8 2.50 0.025 Laborers 6.7 1.50 0.057 Pump runner 1.0 2.00 0.010 Mixing machines 1.7 1.25 0.012

Timber force: Foreman 0.6 2.50 0.008 Carpenters 4.7 2.50 0.057 Laborers 1.2 1.50 0.010 Helpers 5.3 2.50 0.075

Hauling force: Laborers 2.6 1.75 0.026 Teams 6.3 3.25 0.116

Crushing force: Foreman 0.5 2.50 0.007 Engineman 1.7 2.50 0.023 Laborers 3.5 1.50 0.032 Austin crushers 1.7 1.20 0.011

Loading stone: Foreman 1.7 2.50 0.023 Laborers 32.9 1.50 0.280 ------ Total for crushing, mixing and placing $0.975

The daily costs charged to the mixers and crushers include the cost of coal, at $2 a ton, and the cost of oil.

The gang "loading stone" apparently did a good deal of sledging of large stones, and they also wheeled a large part of it in barrows to the crusher.

The plant cost $9,600, distributed as follows:

2 jaw crushers $3,000 2 mixers 3,000 Track 1,260 Lumber 500 Pipe 840 Sheds 400 Pumps 600 ----- Total $9,600

If this first cost of the plant were distributed over the 23,568 cu. yds. of concrete it would amount to 41 cts. per cu. yd.

The cost of the concrete was as follows:

Per cu. yd.

Utica cement, at $0.65 per bbl. $0.863 Portland cement, at $2.25 per bbl. 0.305 Sand, at $1.35 per cu. yd. 0.465 Stone and labor, as above given 0.975 ------ Total $2.608 First cost of plant $0.407

Section 15.--The conditions on this section were much the same as on