38 A TREATISE ON DREDGES AND DREDCilVi 



of 2 dredges, 2 drill boats, one with 4 drills and the other with 2 

 drills; 1 derrick scow with diving outfit, 2 tugs and the necessary 

 dump scows. Over an area of about 39,000 sq.yds. the material 

 was broken up by drilling and blasting. The holes were generally 

 drilled at the corners of 5-ft. squares. The number of holes drilled 

 was 17,212, these being 165,011 lin.ft., showing an average depth 

 of 9.6 ft. per hole. There were removed from an area of 23,000 sq. 

 yds. 33,226 cu.yds. of material, making an average depth of 4.2 ft. 

 This demonstrates that the holes must be drilled to a depth over 

 tw r ice that of the material to be removed. The total hours worked 

 by the drill boaits for all drills was 18,358. This is at the rate of 9 ft. 

 per hour a remarkably good showing. Of the 33,226 cu.yds. of 

 material removed 13,003 cu.yds. were of full-rate material, being 

 above the 22-ft. grade; 17,578 cu.yds. of half-rate material, being 

 between 22- and 24-ft. grades, and 2645 cu.yds. of material for which 

 no payment was made, being below the 24-ft. grade. 



The work on Section 4 was performed by Mr. M. Sullivan of 

 Detroit, Mich., at the contract prices of $2.40 per cu.yd. bank 

 measurement, for material above the 22-ft. grade, and $1.20 per 

 cu.yd. for material between 22- and 24-ft. grades. The contractor's 

 plant was composed of 4 dredges, 4 drill boats, two with 2 drills 

 and two with 3 drills; 1 derrick scow with diving outfit, 3 tugs 

 and the necessary dump scows. Over an area of about 120,000 

 sq.yds. the material was broken up by drilling and blasting. The 

 number of holes drilled was 36,479, there being 260,313 lin.ft., show- 

 ing an average depth of 7.1 ft. per hole. There were used 32S. 1 1 1 

 Ibs. of dynamite, or 9 Ibs. per hole, a little over 1J Ibs. for each foot 

 hole. There were removed from an area of 225,000 sq.yds. 222,635 

 cu.yds. of material, which would give an average depth of nearly 

 3 ft. The holes in this case also were over twice the depth of the 

 removed material. The total hours worked by the drill boats for 

 all drills was 34,729. This is at the rate of 7.5 ft. per hour, or consider- 

 ably less than on Section 2. Of the 222,635 cu.yds. of rock excavated 

 78,260 cu.yds. were of full-rate material, being above 22-ft. grade; 

 100,893 cu.yds. of half rate material, being between 12:2- and 12 1 -ft. 

 grades, and for 43,682 cu.yds. no payment was made, U-in^ In-low 

 the 24-ft. grade. 



Of the total amount of the rock excavated the following shows 

 the percentage of work done as compared with the compensa- 

 tion: 



