is 1 inches; depth of flanges on the inside, 33 inches, with a thickness of 1 inches. These plates are bolted together horizontally and longitudinally with 1-inch bolts. The castings furnished show great accuracy in their casting and tooling, as demonstrated by their perfect fit in place. The lining is set up in rings 4 feet in length, using eight castings for a length, and is backed, when possible, with carefully laid rubble and concrete.

The work began at Station 0 + 60, Rock Creek, west, and was continued west toward the point where the large water flow came through the roof of the tunnel from Rock Creek. The tight rubble masonry was carried up to the point beyond which masonry could not be laid, owing to the rapid flow of water. This flow came through the roof principally in one large stream, falling clear of the sides of the tunnel, and amounting to about 425,000 gallons per diem. At high stages of Rock Creek this amount was nearly doubled.

The rubble masonry backing was carried solid beyond this flow on the side of the lining opposite the stream flowing in from Rock Creek, and the portion on the side of flow for a length of 3 rings, or 12 feet, was carefully packed with dry rubble, then the solid rubble masonry was resumed as packing, confining the water to a space about 12 feet long and 8 feet wide. Holes were drilled in the plates in this area to allow the escape of the water. These holes are five in number-three being drilled for 2-inch vent pipes and two for 13-inch pipes. These pipes will be used as openings through which grouting will be pumped into the voids in the dry packing against the pressure of the water from Rock Creek. About 30 feet beyond this leak another weeper, or vent, 1 inches in diameter, is also drilled for the collection of some small seepage. This will also be grouted.

After passing the leak the lining as above mentioned is solidly backed with rubble masonry, the brick lining of the tunnel having been torn out to insure solid packing.

The total length of iron linings set up was 100 feet completed and backed. For backing, 159 cubic yards of masonry was laid, all of which is solid rubble except about 12 or 15 cubic yards of dry stone in the vicinity of the vent holes.

6. Filling voids in dry-rubble backing.-No work has actually been done under this head, as it is deemed best to leave this until the por tion to be worked is entirely free from other active operations. This work and the washing of the interior of the tunnel with two coats of cement will complete the underground work.

An experiment, however, was made with a view to testing the efficiency of grouting. A model was built 20 feet long to represent dry stone packing of the tunnel. Timber lagging represented the extrados of the brick lining and also the roof and sides of the rock excavation for the tunnel. Grout, consisting of one part hydraulic cement and two of sand, with water enough to render the mixture of proper fluidity to pass the grouting pump, was pumped into the dry rubble packing of the model through auger holes bored in the interior. The cubic contents of the dry rubble was 67 yards, and the voids by rough measurement in water amounted to 50 per cent or 334 cubic yards.

The grout was applied until the voids were filled, as indicated by overflow. There were 75 barrels of cement, 150 barrels of sand, and the proper proportion of water used. The experiment was made in rather unfavorable weather, December, 1898, and during the pumping the thermometer fell below the freezing point. The lagging was stripped from the structure March 1, and the voids were found completely filled,

the structure standing perfectly as a monolith. Photographs showing the result of this experiment are submitted with this report. The conclusion from the experiment is that the grouting can be satisfactorily accomplished.

7. Accessory works.-These include the necessary gatehouses, air shafts, and plant for emptying the tunnel for the purpose of repair or cleaning. Studies and working drawings are being made for these works, to be in readiness for actual work at the proper time.

8. Howard Reservoir.-The Board of experts in their report merely mention this work incidentally, as they were not called on to consider this matter.

The reservoir at present is in the same condition as when work on it was discontinued in 1888.

The revetment of the banks was never carried to the bottom of the reservoir along its whole perimeter. As this is a necessary precaution in any case, authority was granted and advertisements were published inviting bids for furnishing the stone to do this work.

If filtration is decided on it is probable that some alteration or additional work will be required on the reservoir. A project and estimate will be submitted for the completion of Howard University Reservoir at the proper time.

METHOD OF CONDUCTING WORK..

The material was purchased by contract after due advertising, in the case of brick, hydraulic cement, sand, iron lining and bolts for same. Other material was purchased under public notice except in cases when emergency required purchase in open market.

The brick was furnished by the Frederick Brick Works, of Frederick, Md., at $11.40 per thousand. The brick is most excellent in quality and the rejections have been insignificant.

The hydraulic cement was furnished by James H. McGill, of Washington, at 82 cents per barrel, and has exceeded the requirements as

to tests.

The castings for lining Rock Creek tunnel were furnished by the Hoefinghoff & Laue Foundry Company, Cincinnati, Ohio, at $36.40 per ton of 2,240 pounds. They are excellent in quality, are most accurately fitted for place, and are perfectly interchangeable.

The bolts, of satisfactory quality and workmanship, were furnished by Bartlett, Hayward & Co., of Baltimore, Md., at 4.15 cents each.

ORGANIZATION.

The working force is organized into watches, and the watches into gangs, according to their special work. Watches are changed every 8 hours-at 8 a. m., 4 p. m., and 12 midnight.

The work of mucking, removing rock, blasting, backing new lining, and filling voids in old lining was carried on in three watches, work being continued during the twenty-four hours.

The brickwork of new lining and the placing of the iron lining was carried on only during the first watch, or from 8 a. m to 4 p. m.

Work at the head houses at each shaft was continuous, three watches being necessary to run the pumps and elevating cages.

The amount of work accomplished, with the cost, is given in condensed form in the accompanying tables.

LIGHTING THE TUNNEL.

It had been the practice to do all work underground by the light of miners' lamps and torches. This means of illumination is very poor for mechanical work. The fumes and smoke from blasting, added to the smoke from torches and lamps, render the atmosphere underground, especially when the barometric conditions were unfavorable to ventilation, very offensive and discomforting to the workmen. An investigation of the subject of lighting the tunnel by other means, more especially at the locality where the mechanics were at work-brick and stone masons and the workmen on the iron lining-resulted in the selection of acetylene gas as the most available and economical in this special emergency. Accordingly an acetylene gas plant for 300 burners was erected at Champlain avenue shaft, and one for 60 lights at Foundry Branch. The engine houses at the shafts, the head houses, and localities in the tunnel, when required, are lighted by these plants.

Gas pipes were carried down the Champlain avenue shaft and along the tunnel both in an easterly and westerly direction, with cocks for burners at proper intervals, every 30 feet, and this system sufficed for illumination from Rock Creek shaft to Howard University, a distance of over 2 miles. The plant erected at Foundry Branch was in like manner utilized for the illumination from that point in both directions. By connecting with the stopcocks by means of rubber hose a movable light, chandelier or "Christmas tree," of any required number of burners is used, thus concentrating the light in the immediate vicinity of the work, and also enabling the illumination to be carried into the cavities or "crow nests," so called, behind the defective old lining. This method of illumination has proved very satisfactory and quite economical. It is especially valuable as enabling good work to be done and facilitating a thorough inspection of the same.

There are forwarded with this report blue prints from photographs showing the work on the tunnel in various stages; also drawings showing iron lining, cross section of tunnel completed in new work, and cross section of some of the largest voids in old backing.

July 1, 1899, amount covered by uncompleted contracts....

74, 874. 77

95, 795.58

July 1, 1899, balance available

562, 364.89

1901...

(Amount (estimated) required for completion of existing project, including Howard University Reservoir.... Amount (estimated) to be expended in fiscal year ending June 30, 1900. 400,000.00 Amount that can be profitably expended in fiscal year ending June 30,

301,399. 23

139, 034. 34

Abstract of proposals for furnishing and delivering 5,000,000 brick, 20,000 barrels of cement, and 5,000 cubic yards of sand for the work of increasing the water supply of Washington, D. C., received in response to advertisement dated December 27, 1898, and opened January 26, 1899, by Lieut. Col. A. M. Miller, Corps of Engineers.

Abstract of proposals for supplying about 340 tons of special castings and 20,000 bolts for the work of increasing the water supply of Washington, D. C., received in response to advertisement dated December 27, 1898, and opened January 26, 1899, by Lieut. Col. A. M. Miller, Corps of Engineers.