"Assume on the tramways a speed of 200 ft. per minute for the traveling line. The loads could be spaced less than one minute apart, possibly forty to fifty seconds. Assume 1-cu.yd. batches of concrete and the same for an average load of stone. Then the two tramways should put onto the dam 1000 cu. yd. to 1200 cu. yd. per eight-hour shift. This rate could be maintained nearly to the top of the dam; for the top probably but one tramway could be used.
"Starting masonry with two or three towers in the bottom, others could be added in the desired positions as the work progressed. The booms would also be shortened. As the dam got higher, and the ratio of face blocks to filling larger, two shifts of block setting might be required to keep up with one shift of filling. The feasibility of many of the suggested devices has been satisfactorily settled in consultation with a prominent tramway manufacturer".
A possibly desirable modification of the above would be to space the towers closer and to use a heavier standing line/or even a rigid track, for the purpose of handling heavier loads and to withstand the vibration incident to dumping the loads. Although this system could handle stone, it is not to be denied that it would be somewhat simpler and easier to construct and operate it to handle concrete alone. The cableways proposed for setting the face blocks would be necessary for handling forms in case it was desired to build the faces that way.
One other radical departure in method for building dams is inevitably and most forcibly suggested by a consideration of the expansion joint and its logical consequences. If vertical breaks in the longitudinal continuity of a dam are allowable, to say nothing of their desirability, why not take full advantage of them in construction methods? In other words, if the method offers any advantages, start at the top at one end and build across in a succession of vertical sections, finishing each to the top as advance is made. This would permit sending out the concrete in dump cars of large capacity and running on a level on top of the completed sections with the simplest possible installation of tracks.
Much more concrete per trip of containing vessel than by any other present or proposed method would then be feasible. The cars would be moved by an endless traveling cable, would dump without stopping and would be detached from the cable only while being filled at the mixer. As in the previous scheme the gripping and release of the cable would be automatic, and on being filled the cars would go down enough of an incline to acquire the speed of the traveling line.
The extension of the system as the work progressed would be most simple, involving only the shoving ahead of the dumping device and hopper, the introduction of a section of track and the shifting of a tension or take-up sheave at the land end. From the hopper into which the concrete has been dumped it will be delivered wherever desired in the section or sections ahead via one or more pipes or chutes swung from light guys. As concrete will run readily on an angle of about 25 deg. from the horizontal, the entire work can be readily reached for several sections in advance. Indeed, delivery of concrete and several other details of the work will probably be facilitated by working on several sections at a time. Such procedure of alternate delivery to several sections would be highly desirable in connection with the shifting of forms or the setting of face blocks. As in the previous scheme, a couple of cableways would be necessary to handle the face work, whether blocks or forms, and also the forms for the expansion joints. The same cableways or another one could put in whatever stone it might be found economical to introduce.
This method might be criticised in two respects. The first objection is that under the procedure of approaching the deepest and most critical part of the foundation by building down hill toward it, a proper regard for security as to character of foundation as well as the method of building would require that more of the pit would be open at one time, that it would be open for a longer time, and that consequently there would be more pumping and greater liability to interruption from high water. These objections, however, are more apparent than real, and in most cases would be more than balanced by accompanying advantages. Thus it would permit the work to be prosecuted by a larger force during the earlier stages, i.e., during the time usually devoted to constructing the temporary and diversion works and to excavating the pit. If, as suggested, masonry construction was progressing on several sections in steps, high water might rise over the advanced lower step without causing any suspension of the masonry work for some time, or until the remaining steps had advanced to a plumb face at the water's edge, which situation would conduce to still more rapid progress when the pit was again available. If more masonry must be built while the pit is open, it may also be said that more masonry could be built by this method in the same time.
The second objection is that storage of water behind the dam could not begin until a much larger percentage of the total mass of masonry had been placed. While this is absolutely true, the resulting damages and benefits should be balanced as follows in arriving at a decision as to method: The value of stored water should be applied to the time between the date when storage could commence under any other method of construction and the date when it could commence under this method, which difference might not be as great as the relative masses of necessary masonry might indicate. It should be also borne in mind that after storage had once begun the water level could be permitted to rise very much faster under the proposed method of construction than under any method hitherto proposed.
To sum up: Cyclopean concrete has been accepted. The progress already attained with it is four times as fast as rubble masonry. Concrete will be substituted for Cyclopean concrete when it is fully appreciated that the result will be still more rapid progress, further reduction in cost and the elimination of much cumbersome and unnecessary plant.