The limiting depth to which trenches can be excavated by steam shovels is about 20 to 25 feet, where the trench is too narrow for the shovel to enter. Wider trenches are cut in steps of about 15 feet, the shovel working in the trench for additional depths. Shovels are now made to cut trenches as narrow as a man can enter to lay pipe. The greatest width that can be cut from one position of the shovel is from 15 to 40 feet, dependent on the size of the shovel. Occasionally a combination of a drag line and a steam shovel can be used, as on the construction of the Calumet sewer in Chicago. On this work the first step was cut by a steam shovel. It was followed by a drag line resting on the step thus prepared, and excavating the remaining distance to grade. The depth of the trench in this work averaged about 25 to 30 feet.
Fig. 93.—Steam Shovel at Work on Sewer Trench for North Shore Intercepting Sewer, Evanston, Illinois.
Steam shovels are rated according to their tonnage and the capacity of the dipper in cubic yards. Both are necessary as the size of the dipper is varied for the same weight of machine, dependent on the character of the material being excavated. For rock the dipper is made smaller than for sand. Gillette in his Hand Book of Cost Data gives the coal and water consumption of steam shovels as shown in Table 52. The performance of steam shovels is recorded in Table 53. The conditions of the work have a marked effect on the output of the shovel. A shovel in a thorough cut, i.e., in a trench just wide enough for the shovel to turn 180 degrees but too narrow to run cars or wagons along side of it, will perform less than one-half of the work that it can perform in a side cut, i.e., where the cars can be run along side the shovel which turns less than 90 degrees.
| TABLE 52 | ||||||
|---|---|---|---|---|---|---|
| Coal and Water Consumption by Steam Shovels | ||||||
| (From Handbook of Cost Data, by H. P. Gillette) | ||||||
| Weight in tons | 35 | 45 | 55 | 65 | 75 | 90 |
| Dipper, cubic yards | 1¼ | 1½ | 1¾ | 2 | 2½ | 3 |
| Coal, tons per 10 hour day | ¾ | 1 | 1¼ | 1½ | 2 | 2¼ |
| Water, gallons per 10 hour day | 1500 | 2000 | 2500 | 3000 | 4000 | 4500 |
| TABLE 53 | |||||||
|---|---|---|---|---|---|---|---|
| Performance by Steam Shovels | |||||||
| Weight in Tons | Dipper Cubic Yards | Depth of Cut, Feet | Width of Cut | 10–Hour Performance | Cost in Cents, per Cubic Yard | Authority | Remarks |
| 25 | 1 | 9 | 36 in. | 85 | 22.6 | R. T. Dana Eng. Rec., 69:581 | 1 |
| 25 | 1 | 8 | 35 in. | 96 | 23.5 | do. | 2 |
| 70 | 2 | 26 | 16 ft. | 569 | 6.7 | do. | 3 |
| 30 | 1 | 15–18 | 60 in. | 300 | A. B. McDaniel Excavating Machinery | 4 | |
| 15 | ⅝ | 14 | 134 ft. | 400 | Eng. Cont’r, 8–25–09 | 5 | |
| 8 | 36 | Very wide | 16 yd. cars | Marion Steam Shovel Co. | 6 | ||
| 55 | 296 | H. P. Gillette’s Cost Data | 7 | ||||
| 65 | 2¼ | 280 | do. | ||||
| Greater than 78 in. | 700 | 30.6 | G. C. D. Lenth, Eng. News-Record, 85:22 | 8 | |||
Remarks: 1. One runner at $5.00, one fireman at $2.31, two laborers at $1.70 each, supplies at $4.50, and interest and depreciation on 200 days per year, $4.00. Total per day, $19.21. Material, clay and gravel. 2. Average of 11 jobs with the same shovel. 3. Cost per day, one runner at $5.00, one crane-man at $3.60, one fireman at $2.00, 7 roller men at $1.50 each, supplies $9.00 and interest and depreciation on $9000 at 200 days per year $8.00. Total, $38.10. 4. Hard clay. 5. Stiff clay for the basement of a building in Chicago. 6. Stripping ore. This is a maximum record. The average was about three hundred and twenty 16 cubic yard cars per day. 7. Blasted mica-schist. 8. General average.
134. Drag Line and Bucket Excavators.—A drag line excavator is shown in Fig. 94. The back of the bucket is attached to a drum on the engine by means of a cable passing over the wheel in the end of the long boom. The front of the bucket is attached by another cable directly to another drum on the engine. In operation the bucket is raised by its rear end and dropped out to the extremity of the boom. It is then dragged over the ground towards the machine, digging itself in at the same time. When filled the bucket is raised by tightening up on the two cables, swung to one side by means of the movable boom, and dumped.
Fig. 94.—Drag Line at Work on Trench for Drain Tile.