COMPARATIVE METHODS OF EARTH EXCAVATION AT COLBERT SHOALS CANAL

BY

Mr. CHAS. E. BRIGHT
Superintendent

Colbert Shoals Canal, which was designed to overcome the obstructions to navigation at Colbert and Bee Tree Shoals, is located along the south, or left bank, of the Tennessee River; the lower end of the canal being about one-half mile above Riverton, Ala. It is a lateral canal 8 miles long, with a lock of 26-foot lift, 80foot width, and 350-foot length, located at the lower end. Beginning at the upper end of this lock and extending upstream for a distance of 5.3 miles, the canal was excavated through the bottom lands, the cutting ranging in depth from 17 feet at the lower end to 20 feet at the upper. Above this, by reason of the close proximity of the bluffs to the water's edge, the canal was formed by building a concrete wall in the river about 180 feet from the left shore line, for a distance of 1.4 miles, and above this, on account of its being more economical than excavating through the bottom lands as originally proposed, the river side of the canal was formed by building a levee in the river with the material excavated in bringing the canal to the required depth.

As the excavation of the canal for 5.3 miles through the bottom lands is the only portion of the canal to be considered in this paper, the formation, topography, location, and character of that material will be described.

The bottom lands are of an alluvial formation, and as is usual along silt bearing streams, are highest near the top of river bank, sloping gradually from this point to the foot of the hills. It is presumed that the canal was located close to the foot of the hills for the purpose of reducing the quantity of excavation. As is natural to suppose, the expensive material was found mostly on the side of the canal next to the hill, and part of the canal was so close to the hills that no material could be deposited on the land

side of the canal. This necessitated the wasting of all material on the river side of canal, which increased the haul by teams and also caused some of the material to be handled twice, when using the drag-bucket excavators. With the exception of a distance of about 1,300 feet, where the slope stakes are within a few feet of the top of the river bank, there is a strip of bottom land between the present location of the canal and the river which varies in width from 400 to 700 feet. This provides ample room for the location and also permits the elimination of several curves, and though this ground is slightly higher than that through which the canal now runs, the additional expense of handling the increased yardage would have been more than counterbalanced by the cheapness of removing the drier and softer material.

The cross section of the canal is 112 feet wide at the bottom or at grade, with side slopes of 1 on 2. Berms 15 feet wide between slope stakes and the toe of spoil banks were left on both sides of the canal, the berm on the river side being brought to a height of not less than 9.5 feet above low water in the canal.

The excavation for forming the canal trunk between the upper end of the lock and the lower end of the concrete wall was made under four separate contracts, as follows: The first covering Stations 10-110, and the second covering Stations 110-210, were dated October 12, 1905; the third, covering Stations 210-260, dated March 12, 1905. All of the above contracts were awarded to Shippey & Outzen, Memphis Tenn., at 17.49 cents per cubic yard for earth, 50 cents per cubic yard for hardpan, and $1 per cubic yard for rock, the price for the last two items being fixed by the Government. The fourth contract, covering Stations 260-290, dated April 7, 1908, was awarded to W. A. Shippey and the North Alabama Construction Company, at 24.9 cents per cubic yard, unclassified.

The work of excavation was commenced November 15, 1905, immediately above the lock, with wheel scrapers and Western elevating grader, drawn by traction engines, and served by Aurora dump wagons of 1% cubic yards capacity. As the grass and cornstalks clogged the elevator of the grader, it was necessary to use the wheel scrapers to strip the surface before the graders could be successfully used. On account of the soft, sticky condition of the material, being what is usually termed "gumbo," it was soon learned that the elevating graders were not adapted to the work, and arrangements were made by the North Alabama Construction Company, sub-contractors, Stations 10-135, for installing Arm

strong excavator machines using the Page drag bucket. Two of these machines were erected and began work on the 24th of February, 1906, at Station 20. These machines having proved more satisfactory than the elevating grader, the work with graders was discontinued after January 1, 1907, the teams sold, and a third revolving excavator was purchased; these three machines being used exclusively after this date on all the work done by this company, being about 889,000 cubic yards. Shippey & Outzen used wheel scrapers and elevating graders, drawn by traction engines and served by eight four-horse dump wagons to each machine, on all the work performed by them, which amounted to 767,000 cubic yards. On account of the hill being so close to the river bank between Stations 196-222, the greater part of the material would have had to be handled twice with Armstrong excavators, and since the ground was too steep to use grading machines, a steam shovel was procured for this section of the work.

All of the graders used were what is termed "Standard Western Elevating Graders," with 21-foot elevator, using an extra heavy or giant railroad plow for loosening the material and throwing it on the elevator. This plow was attached to one side of the frame of grader. The only portion of the canal completely excavated to grade by these machines was from Stations 10-20 and 145-163, which proved unprofitable on account of the material usually becoming too hard near the bottom to be loosened by the plow, and the height to which the material had to be lifted in getting it to spoil banks too great. These machines, in connection with wheel scrapers, were most successfully used in making a cut from 8 to 12 feet in depth, and 110 to 120 in width, off the top. This left a strip about 30 feet wide inside the slope stakes on each side for the drag bucket excavators to work from in taking out the remainder of the section. This arrangement gave the elevating graders the soft material to which they were best adapted, and, at the same time, the least lift in conveying the material to spoil banks. This method was practiced between Stations 222-290, and accounts for the low cost of work done by these machines on this section.

The steam shovel outfit consisted of a 65-ton Marion shovel, one 25-ton and one 20-ton dinkey locomotive, and eight "Oliver' 12-yard, side dump cars, all standard gage; with about 1/4 miles of track, a tank, and pipe line and pump for supplying water to shovel and locomotives. The steam shovel outfit, working between

Stations 196-222, was profitably used in taking down the hillsides and removing the dry material from the top of the cut, but as the depth of the cut increased below the top of spoil banks, the two trains were unable to supply the shovel with empty cars fast enough to keep it busy, and, finally, after having made one cut through to grade, the bottom was found to be so soft that it was impracticable to work the shovel and it was removed to another part of the work and the Armstrong excavators were used to remove remaining 42,000 cubic yards.

The two Armstrong excavating machines consisted of a bottom. wooden frame which rested on wooden rollers placed on skids, and

on this frame was a spider about 20 feet in diameter, carrying sixteen dollies which revolved on a circular track made of 90-pound rail. This supported the heavy top frame which carried the machinery, boiler, tank, fuel, and derrick. The top frame is revolved by a single drum reversible engine, the wire line being carried from the drum by sheaves to the steel rail placed underneath the top frame; this rail serving as a bearing for the dollies, and also a drum for the swinging line, the ends of which were attached to it. The top and bottom frames were provided with central pin and socket castings which held the top frame and spider in place. A boom 81 feet long was attached to one end of the top frame and

stood at an angle of 30 degrees from the ground. A double drum hoisting engine, 10 by 12 inches, was located a little back of the center of the frame, and the boiler and tanks were located well back to counterbalance the weight of the boom and bucket. The Page scraper bucket of 2 cubic yards capacity was used, rigged with a hoisting line from one drum of engine, passing over the end of boom, using two single blocks and attached to the back bail of bucket, with a loading line from the other drum passing through a sheave attached to the front bail of bucket, then brought back and attached to the top frame, under the boom. The MeMyler machine was rigged the same as the Armstrong machines and was similarly constructed, except that the frames were of steel, mounted on trucks, and was revolved by a circular rack attached to the bottom frame and a pinion geared with hoisting engine, and used a 12 cubic yard bucket. Where these machines were used the surface was usually stripped to a depth of from 4 to 12 feet by elevating graders and wheel scrapers, leaving a strip about 30 feet wide inside the slope stakes on each side for supporting the drag-bucket machines. This was done for the purpose of preventing the spoil banks from becoming too high for dumping. One Armstrong machine was usually kept in front taking the excavation to grade from the foot of the slope to center line, with the McMyler following trimming the slope, and the other machine following on the opposite side, removing the remainder. This arrangement is shown in the two illustrations.

The methods of excavation having been described, the following table shows the quantity handled and the comparative cost of each method. The cost, as given in these tables, includes labor, material, repairs, fuel, feed and care of live stock, and running expenses during delays occasioned by high water and bad weather, but makes no allowance for depreciation of plant or interest on money invested in plant.