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The following is an outline of the history of operations during year, and further details are given in the report of Lieut. C. M Townsend, Corps of Engineers, submitted herewith:

DAM AT THE GREAT FALLS.

At the beginning of the year this work required the placing of or 192 linear feet of coping for its completion. This was accomplish without difficulty, and the contract closed August 21, 1886.

The total length of the dam as now completed is 2,877 feet; of t length 1,034 feet is comprised in the old dam closing the Maryla: Channel, which was raised to the designated height by placing a coing 15 inches thick. The next stretch of dam crosses Conn's Islan and is 669 feet long; the remaining 1,174 feet closes the Potomac Chan; nel. The new part of the dam varies from 4 to 20 feet in height. The final estimate of work done by the contractors was as follows: 1,086.3 cubic yards coping masonry, at $24.50 1,989.7 cubic yards cut-stone masonry, at $20.75 2,820 cubic yards concrete masonry, at $5.50 8-9 cords riprap backing, at $7.25.

34,166 pounds wrought-iron drift bolts and cramps, at 7 cents 5,695 cubic yards excavation, at $1 ...

9,500 square yards area cleared, at 5 cents..

26, 614.

41, 24.7

15,510.

6,445.

2,391.

5, 196

475.

EXTRA MATERIAL AND LABor.

224 cubic yards concrete masonry, at 50 cents..

40 barrels Portland cement, at $2.70

1 barrel Portland cement, at $3.75

124.5 barrels Cumberland cement, at $1.15

75 cement sacks, at 15 cents

27.57 yards coarse sand, at $1.20

2 yards fine sand, at 60 cents

3 yards clay, at $1.25.....

531.38 square feet fine pointing, at 30 cents

34 linear feet stop-notches, at $3.50..

Pay-roll for services in July, 1885

Making deflecting-dams, coffer-dams, sluices, and all other work required,

as per supplemental contract

Total.....

Work, etc., under original contract.

For extra work and material..

Supplemental contract......

Total paid contractors

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Of the above amount the sum of $3,216.47 only was for work done during the past fiscal year. The amount expended from the beginning on account of surveys, engineering, superintendence, contingencies, etc.. is $10,976.46.

The original appropriation was..
Deduct amount paid contractors
Deduct expenses of surveys, engineering, etc..

Balance on hand................

$145, 151.00

$114, 509.02
10, 976. 46

125, 485.45 19, 665.52

There was also appropriated a sum of $45,000, to pay for land and water rights at the Great Falls, but these matters are pending in court in charge of the Attorney-General. No expenditure was made on account of this appropriation during the year, and in all only $117.96 has been expended therefrom, as stated in previous reports.

TUNNEL FOR AQUEDUCT EXTENSION.

At the beginning of the fiscal year no work was in progress, operations having been suspended February 1, 1886, when the original ap propriation for the work became exhausted; at that time the tunnel had been excavated through a length of 18,538.2 feet, of which 1,489.66 feet had been lined, the lining consisting of a facing of brick masonry laid in hydraulic cement mortar, with a backing of concrete for the invert and side walls, and a packing of dry stone, carefully placed, to fill in the space comprised between the arch and the rock through which the tunnel was excavated.

The suspension of operations continued until after the passage of the general deficiency bill approved August 4, 1886, which contained an appropriation of $395,000 for completing the tunnel. This appropriation was made after prolonged investigation by the House Committee on Appropriations, as the result of criticisms in which the method of doing the work, especially the character of lining, was fiercely assailed. Full record of this investigation is found in H. R. Report No. 3109, Forty-ninth Congress, first session, of which 70 pages out of 84 are devoted to this subject. As a result of this investigation the committee reported that it was not convinced that a mistake had been made in the plans adoptedfor lining the tunnel, "but recognizing the difficulty, the novelty, and the importance of these questions and the expediency of submitting them to competent experts (the committee) have, in recommending the amount called for by the estimates, provided that the Secretary of War shall forthwith take the advice of the highest Engineer Board of the Army upon the plans and methods heretofore pursued." Accordingly the appropriation of the amount called for was coupled with the conditions that the Secretary of War should "submit to the Board of Engineers for Fortifications and for River and Harbor Improvements whether any changes are demanded for reasons of safety or economy in the method of lining said tunnel heretofore adopted and pursued, and whether any changes are required in the method of lining and perfecting the reservoir: Provided, That said board shall make full report thereon, and pending such examination the work shall proceed upon such parts thereof as the Secretary of War shall direct. The work above provided for to be done under the contract heretofore made or by a reletting, as in the discretion of the Secretary of War shall be most promotive of the interest of the Government."

In pursuance of this legislation it was determined to continue the work of excavation under the original contract (see copy of correspondence herewith), and this part of the work was resumed August 30, 1886, and continued without interruption until the close of the fiscal year, when the tunnel was "holed" through. The work of excavation remain. ing to be done after that date was only such as will be required from enlarging and trimming to the requisite lining or normal cross-section. In the mean time the matters in question were promptly submitted to the Board of Engineers, as directed by Congress, and after careful examination and personal inspection of the tunnel the Board made its report thereon August 24, 1886, a copy of which was received by me from the Secretary of War August 27, 1886. In this report the Board concluded that the exclusive use of concrete for lining (as had been urged in the strictures against the method formerly adopted) was impracticable, indorsed the use of the brick arch as then being constructed, but recommended that the filling between this arch and the rock in place be done "with rubble laid in cement mortar, or with fine concrete

packed solidly around larger stones according to convenience," instra. of with dry-stone packing. After careful deliberation (see correspon ence herewith) supplemental articles of agreement were entered i with the contractors on the work, providing for the use of rubble = sonry, no provision for that class of work having been made in the or: inal contract. The cost of packing or filling was thereby increased in: $2.50 to $4.75 per cubic yard. Operations on the work of lining wer then resumed, and the total length of tunnel lined up to the close of the fiscal year was 6,110.5 feet. Operations during the year were conducte without loss of life or serious accident of any kind.

The total estimate of work done by the contractors on the tunnel = to June 30, 1887, is as follows:

73,551 cubic yards excavation in tunnel, at $8.
2,148.75 cubic yards earth excavation in shafts, at $6.
2,676 cubic yards rock excavation in shafts, at $10
7,828 cubic yards brick masonry in tunnel, at $14.
2,014 cubic yards concrete masonry in tunnel, at $5.
4,936.72 cubic yards dry-stone packing in tunnel, at $2.50
383 cubic yards brick masonry in shafts, at $18.
600 cubic yards concrete masonry in shafts, at 85
930 cubic yards dry-stone packing in shafts, at $2.50
444 linear feet air-shafts complete, at $15.

637.78 cubic yards extra excavation in tunnel, at $1.50.
10,178 cubic yards rubble masonry in tunnel, at $4.75.

Total for contract work....

Paid contractors for pumping

Total cost of work done.....

Deduct 10 per cent. retained on contract work.

Amount paid contractors....

$588.48
12,
1265, 76008
109,32%
10.G
12,341.

6,1

3,00

2,354

6, 2

48,345.

828,245. C

7,036.1

835,980.

82,824. A

752, 456.

Of the above total the sum of $261,110.81 is for work done during the past fiscal year.

In addition to the above total there have been expended from the ap propriations for aqueduct extension the following sums:

For west connecting conduit (1886) ...........
Engineering, superintendence, and contingencies, including cost of pre-
liminary surveys and examinations (1882-1887).

Total.....

$5,006.2

35, 410.

40,416.

This, added to the total cost of work done by the contractors, makes the grand total of expenditures up to June 30, 1887, including out standing liabilities and retained percentages, $875,696.85.

The appropriations have been as follows:

Act approved July 15, 1882

Act approved March 26, 1886 (pumping)........
Act approved August 4, 1886..

Total appropriated...................

$599, 334.5 5,000. 395, 000, 0

999, 534, 5

Deducting therefrom the total expenditures and liabilities ($875,696.85 to June 30, 1887, the balance available at that date was $123,837.70 The estimate on which the deficiency appropriation of $395,000 was made in 1886 was prepared in the summer of 1885, when but little more than one-half the length of the tunnel had been excavated, and therefor the character of rock to be encountered in the then unopened parts was purely a matter of surmise. This estimate assumed that only about one half the tunnel would require lining. Again, this estimate presumed the use of dry-stone packing as comprising the most considerable par:

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