Nearly five years ago the writer proposed the following plant and method for constructing a large masonry dam:

"Assuming the body of the dam to be of concrete with large stone embedded in it, and the faces of the dam to be of concrete blocks. For handling the material for the body of the dam, equip with two Leschen or similar tramways; each to consist of one standing cable extending across the dam and back, and one traveling line moving continuously and in one direction; the two to be supported by towers comparatively close together.

"The advantage of this tramway is that with a given speed of traveling line the capacity is limited only by the number of loads that can be attached per minute, whereas an ordinary cableway must make the entire length of the trip and return, coming to a stop twice for each load conveyed. The tramway is to be supported by towers say 150 ft. apart to permit good-sized loads to be carried on a moderate-sized standing line without excessive sag. {See Fig. 37 herewith.) Across the masonry at least, these towers should be something as shown in Fig. 38, made of regular rolled steel shapes. The masts are to be built into the dam and left there, although they would have to be shifted in position several times as the dam grew higher. Between the points marked "A-A" (Fig. 38) would be introduced sections in 10-ft. or 15-ft lengths as the work raised, the upper part of the tower with the boom being jacked up while the section was being inserted. The supports "B-B-B-B" (Fig. 38) for the tramway would be capable of being readily moved along the boom in order that the whole width of the work may be covered. In connection with the lateral movement of the tramways, the loads could be automatically dumped at any point in the length of the dam, thus covering the whole work.

Possible scheme for conveying concrete to a dam.

Figs. 37-39. Possible scheme for conveying concrete to a dam.

"Referring to Fig. 39, it will be appreciated that this system is quite flexible. The tramway can be carried as far up the hill, also as far to one side as desired within reason, without cutting down the capacity, so that it permits considerable departure from the assumed relative positions of the dam, quarry, sand plant, mixer and cement storage. The empty buckets on reaching the points marked "D" would be automatically released from the traveling line and switched onto the side track under the mixer. After being filled they would be started down an incline of sufficient length and inclination to acquire the speed of the traveling line; at "E" they would go onto the standing line again and automatically grip the traveling line.

"At similar loading stations on the quarry the tramway could take up chunks of stone, using the same kind of bucket for small chunks as for the concrete. For large chunks eliminate the bucket and use chain and hooks, which can also be arranged so as to release automatically. One or two steam shovels in the quarry should deliver rock to conveyors running to crushers in the rock and sand plant. The finest portion of the output of the crushers will go to rolls for reduction to sand. The screen between the crushers and the rolls could probably be arranged so that the amount going to the rolls would furnish just sufficient sand to accompany the crushed rock; if so, the stone and sand could probably go to one bin, and from there go via one conveyor to the mixer. At the mixer should be devices for very rapidly measuring the cement and the product of the sand and rock plant.

"Two Hains (or similar) gravity mixers, one for each tramway, should be provided. The bottom hopper should have a gate to regulate the amount and time of delivery to the buckets.

"There should be ample cement storage, for cement either in sacks or in bulk as the case may be, with a belt conveyor to the mixer. Near the mixer should be the concrete block factory with tracks to the storage yard. The yard could be say 50 ft. wide and as long as necessary. It should be spanned by one or two traveling cranes of one-block capacity to handle the blocks coming from the mixer and the blocks going to the dam. A large part of the blocks should be made and in the storage yard before work on the actual masonry construction commences; the height to which they can be piled in the yard would be limited by the height of the traveling cranes. From the yard the blocks would be taken by platform cars or some form of conveyor to two cableways, one over each face of the dam. These cableways are shown at 'C-C,' Fig. 38. The carriage and hook travels out and back; out with a concrete block, stopping at the proper point, the block lowered into place and then back for another load. About two block setters will work on each face. Between trips they will prepare a mortar bed for the next block and fill up the vertical joint just made. Occasionally the cableway will make a trip with a small skip of mortar and return with an empty skip. As the blocks would be of uniform and accurate dimensions, they could be set rapidly, especially as the cableways (like the tramways) could be shifted laterally so as to hang over the center of the course it was laying. There would be no men on the dam except the face block setters, and a man or two to keep the work wet down. Slung between the towers at the level of the boom should be a light foot bridge. From this bridge one or two directors will watch the work and direct it by electric signals, calling for concrete or stone as may be desired, for any desired lateral shifting of the tramways and for any setting of the automatic dump.