Another leading consulting engineer stated that he had reported adversely on a proposition for building a 300-foot reinforced concrete pen stock. He was afraid of seepage and freezing.
An engineeer experienced in government work believes that, if properly designed, a pen stock could be built of reinforced concrete with out expansion joints.
The president of a large manufacturing com pany had had experience with a steel penstock 15 feet in diameter and 300 feet long, which crawled 3 inches and tore loose from the dam.
Although the chief engineer of a mill engi neering firm had no direct knowledge of rein forced concrete penstocks, he had had trouble with those built of steel. These he had to cover.
An engineer experienced in the building of sewerage disposal works believed that such pen stocks could be built with success, and that the leakage would be small; also that it would be essential to cover the concrete mass sufficiently to equalize the temperature.
Mr. Wason's conclusion was that it is feasible to build a penstock of reinforced concrete with out joints; that care would have to be taken to make proper bond between days' work; and that, even with this care, slight leakage would be likely to occur at these joints when the penstock was first put into use. His experience in the matter of subsequent closing of leaks came largely from the building of the notable stand pipe at Attleboro, Mass. This is 50 feet in di ameter with 100-foot water head. When first built, it leaked; but an application of the "Syl vester solution" to the inside stopped all leak age, and to-day the pipe is tight. In order to get these results it is necessary to have proper de sign and very careful workmanship.
Reservoirs. In a bulletin on the design of reinforced concrete reservoirs, issued by the Cor rugated Bar Company of St. Louis, Mo., the fol lowing very pertinent general observations are made: "The exterior walls of reservoirs must be designed as dams to resist the lateral pressure of the water, and also as retaining walls capable of holding the earth back ing should the reservoir be built in excavation or the side walls be banked with earth. Reservoir walls are then
practically retaining walls, and a reinforced concrete design will be superior to a heavy masonry or plain con crete structure. In fact, the features which make rein forced concrete so desirable for the construction of retain ing walls make it even more desirable for the construc tion of reservoir walls. Briefly summarized, the advan tages of a reinforced concrete design over these others are as follows: "1. Greater stability at less cost.
"2. Lower and more uniform soil pressure.
"3. The practicability of reinforcing against tem perature stresses.
"4. The possibility of using such sections as could not be constructed of the other materials generally used.
"For the construction of the roof of covered reser voirs, especially when an earth fill is to be placed upon it, reinforced concrete, owing to its permanence, is superior to all other usual materials, as the elements of decay and corrosion are most active under such conditions.
Reservoirs of rectangular shape may be roughly di vided into two classes; first, those with vertical side walls; second, those with sloping exterior walls. We are not considering those structures in which the reinforced concrete construction merely acts as a lining for the earth embankment.
"Type 1.—Vertical Walls. This type of reservoir is usually constructed partly in excavation; the excavated material is generally used as a backing for the walls. The backing must not, however, be relied upon to assist in maintaining the stability of the wall. It is possible that the fill may exert no active pressure on the wall; in fact, when the fill is mainly clay, it may even shrink away from the back of the wall. (Such materials as sand or other granular substances without cohesion between the particles, will, of course, exert an active pressure.) The walls then should be designed as retaining walls to hold back the earth when the reservoir is empty, and must also be figured for the water pressure, neglecting such horizontal earth pressure as may exist.