Part 61 (2/2)

MISCELLANEOUS DATA ON MATERIALS, MACHINES AND COSTS.

The following cost data comprise such miscellaneous items as do not properly come in the preceding chapters. They are given not as including all the miscellaneous purposes for which concrete is used but as being such items of costs as were secured in collecting the more important data given in preceding sections.

[Ill.u.s.tration: Fig. 303.--Device for Drilling Green Concrete.]

~DRILLING AND BLASTING CONCRETE.~--Concrete is exceedingly troublesome material in which to drill deep holes, and this statement is particularly true if the concrete is green. The following mode of procedure proved successful in drilling 1-in. anchor bolt holes 6 ft.

and over in depth in green concrete. The apparatus used is shown by Fig.

303, re-drawn from a rough sketch made on the work by one of the authors, and only approximately to scale. The drill is hung on a small pile driver frame, occupying exactly the position the hammer would occupy in a pile driver, and is raised and lowered by a hand windla.s.s.

By this arrangement a longer drill could be used than with the ordinary tripod mounting and less changing of drills was necessary. A wide flare bit was used, permitting a small copper pipe to be carried into the hole with the drill; through this pipe water was forced under pressure, carrying off the chips so rapidly that no wedging was possible. By this device drilling which had previously cost over 25 cts. a hole was done at a cost of less than 5 cts. a hole.

In removing an old cable railway track in St. Louis, Mo., holes 8 ins.

deep were drilled in the concrete with a No. 2 Little j.a.p drill, using a 1-in. bit and air at 90 lbs. pressure. A dry hole was drilled, the exhaust air from the hollow drill blowing the dust from the hole keeping it clean. The concrete was about 18 years old and very hard. Two holes across track were drilled, one 10 ins. inside each rail; lengthwise of the track the holes were s.p.a.ced 24 ins. apart, or four pairs of holes between each pair of yokes.

Common labor was used to run the drills and very little mechanical trouble was experienced. Three cars were fitted up, one for each gang, each car being equipped with a motor-driven air compressor, water for cooling the compressors being obtained from the fire plugs along the route. The air compressors were taken temporarily from those in use in the repair shops, no special machines being bought for the purpose.

Electricity for operating the air compressor motors was taken from the trolley wire over the tracks. The car was moved along as the holes were drilled, air being conveyed from the car to the drills through a flexible hose. Two drills were operated normally from each car. One of the air compressors was exceptionally large and at times operated four drills. The total number of holes drilled in the reconstruction of the track was 31,000. The total feet of hole drilled was 20,700 ft.

With the best one of the plants operating two to three drills 30 8-in.

holes, or 20.3 ft. of hole, were drilled per hour per drill at a labor cost of 2.7 cts. per foot.

For blasting, a 0.1-lb. charge of 40 per cent. dynamite was used in each hole. A fulminating cap was used to explode the charge, and 12 holes were shot at one time by an electric firing machine. The dynamite was furnished from the factory in 0.1-lb. packages, and all the preparation necessary on the work was to insert the fulminating cap in the dynamite, tamp the charge into the hole and connect the wires to the firing machine. In order to prevent any damage being done by flying rocks at the time of the explosion, each blasting gang was supplied with a cover car, which was merely a flat car with a heavy bottom and side boards.

When a charge was to be fired, this car was run over the 12 holes and the side boards let down, so that the charge was entirely covered. This work was remarkably free from accidents. There were no personal accident claims whatever, and the total amount paid out for property damages for the whole six miles of construction was $685. Most of this was for gla.s.s broken by the shock of explosion. There was no gla.s.s broken by flying particles. The men doing this work, few of whom had ever done blasting before, soon became very skillful in handling the dynamite, and the work advanced rapidly. The report made by the firing of the 12 holes was no greater than that made by giant fire-crackers.

For the drilling and blasting the old rail had been left in place to carry the air compressor car and the cover car. After the blasting, this rail was removed and the concrete, excavated to the required depth. In most cases the cable yokes had been broken by the force of the blast.

Where these yokes had not been broken, they were knocked out by blows from pieces of rail. The efficacy of the blasting depended largely upon the proper location of the hole. Where the holes had been drilled close to the middle of the concrete block, so that the dynamite charge was exploded a little below the center of gravity of the section, the concrete was well shattered and could be picked out in large pieces.

Where the hole had been located too close to either side of the concrete block, however, the charge would blow out at one side and a large ma.s.s of solid concrete would be left intact on the other side. The total estimated quant.i.ty of concrete blasted was 6,558 cu. yds., or 0.2 cu.

yd. of concrete per lineal foot of track. The cost of the dynamite delivered in 0.1 lb. packages was 13 cts. per pound. The exploders cost $0.0255 each.

The cost of drilling and blasting was as follows:

Item. Per mile. Per lin. ft. Per cu. yd.

Labor, drilling $ 89.76 $0.017 $0.085 Blasting labor and materials. 285.12 0.054 0.268 ------- ------ ------ Total drilling and blasting. $374.88 $0.071 $0.353

[Ill.u.s.tration: Fig. 304.--Bench Monument, Chicago, Ill.]

The cost of blasting with labor and materials, separately itemized, was as follows, per cubic yard:

Dynamite and exploders $0.192 Labor 0.076 ------ Total $0.268

Two cubic yards of concrete were blasted per pound of dynamite.

~BENCH MONUMENTS, CHICAGO, ILL.~--The standard bench monuments, Fig. 304, used in Chicago, Ill., are mostly placed in the gra.s.s plot between the curb and the lot line, so that the top of the iron cover comes just level with the street grade or flush with the surface of the cement walk. The monument consists of a pyramidal base 6 ft. high and 42 ins.

square at the bottom, with a -in.2-ft. copper rod embedded, and of a cast iron top and cover constructed as shown by the drawing. Mr. W. H.

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