THE IRKIGATION AGE. 



239 



ANOTHER STEP 



The development of the Reinforced-Concrete 

 Dam has demonstrated that there was room 

 for good thinking along the line uf Hydraulics. 

 There is still room. 



The Hollow Core Wall for earth embank- 

 ments or hydraulic fills which is the subject 

 of this advertisement, is so obvious at a glance 

 that but little discussion is necessary. 



Figure 1 shows the approximate line of 

 saturation of the ordinary earth dam, the sec- 

 tion being that of the famous Necaxa dam in Mexico which sloughed 

 out during construction. The control of the "line of saturation" 

 has been the perplexity of engineers since earth dams were built. 



It is well understood that the saturated under-body of an earth 

 dam becomes a lubricated plane on which the whole structure is 

 liable to slip. In other words, the ordinary earth dam is upside 

 down as regards stability. Puddle walls of clay, concrete core walls, 

 etc., have been and still are used and serve a certain purpose. But 

 a clay wall is not impervious to boring animals or immune against 

 shrinkage, and a concrete core wall, if massive, is very costly, and 

 if light, is liable to destructive distortion. 



Furthermore, the material in the dam loses effective weight in 

 proportion to its buoyancy. The degree varies with the natu're of 

 the material but some loss always exists. Thus, if the material were 

 supposed to be open gravel weighing, when dry, say 120 pounds 

 per cubic foot when submerged it would 

 weigh only 84 pounds per cubic foot 

 owing to the displacement of the water 

 and allowing 40 per cent of voids; and 

 similarly with other material. The down 

 stream prism of the dam being protected 

 by the hollow core wall is always dry 

 and therefore always up to full efficiency 

 and weight. 



One of the salient features of the 

 Ambursen Dam which received instant 

 recognition at the hands of engineers 

 and laymen alike was the facility af- 

 forded for absolute inspection of every 

 square foot of its interior. We have 

 now done the same thing for the earth 

 dam and at no sensible increase of 

 cost. 



The Hollow Core Wall is built of 

 reinforced concrete, u'sing a system of 

 slip forms which admit of rapid and 

 economical construction. It consists of 

 two comparatively thin parallel walls 

 spaced by ribs which are monolithic 

 with the whole structure, and capable 

 of withstanding the external earth 

 pressure. The up-stream wall is keyed 

 into the impervious sub-structure wheth- 

 er of rock, clay, hardpan, etc. , ef- 

 fectually intercepting the "creep" of 

 water along the junction plane. In 

 the illustrative section the substructure 

 is shown as rock, although the occa- 

 sions are comparatively rare when the 

 immediate foundation of an earth dam 

 is of this material. 



The down-stream wall need not be 

 keyed in at all, or at most but slightly. 

 If deep lying water-bearing seams are 

 suspected they may be reached and 



tapped off by a series of drill holes along the bottom of the core 

 wall. 



Drain pipes with open joints and of large capacity are led from 

 the core wall at frequent intervals out through the embankment, 

 discharging into gutters on the down-stream side. The joints are 

 cemented as they approach the toe of the embankment in order that 

 they may not be clogged by penetrating roots. 



It is obvious that any water which may find its way through the 

 sub-material or which may come through any joints in the core wall, 

 or from any source whatever, is absolutely intercepted by the hollow 

 wall and drained away. For the first time, therefore, we have se- 

 cured an absolutely dry earth prism for the down-stream section 

 of the dam, thus materially increasing its stability. 



*'> 



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FIGURE 1. Line of saturation and slip. Necaxa Dam. 



Moreover, the Hollow Core Wall penetrates the heart of the 

 whole mass. It is well lit from above and is accessible by a per- 

 manent ladder-way of iron rungs extending to the bottom. Open- 

 ings through the parti-walls at various levels give access to every 

 foot of both su'rfaces. Any unsuspected leak may therefore be lo- 

 cated and if possible remedied. If it is not serious enough to 

 be troublesome, or if it is incapable of being remedied, we at least 

 make certain that it is powerless for harm. 



The Hollow Core Wall is arranged to be covered by plank tom- 

 pions in the winter, so that the space is not filled with snow and 

 ice. 



Figure 3 is a photograph of the little earth dam in the famous 

 Horseshoe Bend on the Pennsylvania road near Altoona. This dam 

 is so located that it is subject to violent wind gusts down a gorge 



FIGURE 2. Earth Dam with Hollow Core Wall and Drains. 



of the mountains. A few years ago such a gust pushed the water 

 to the lower end of the dam and actually blew it over the edge 

 of the dam. The result was the beginning of a severe wash, as 

 shown in the illustration. 



Now, in many locations, notably in Colorado, and the states on 

 the eastern slope of the Rocky Mountains, the slope of the land is 

 such that the dams are in the southeast ends of the valleys. The 

 prevailing heavy winds are from the northwest, and hence a wave 

 ru'n is set up which expends its full force on the dam and is a 

 serious menace. 



To meet this we carry the down-stream wall up somewhat above 

 the level of the embankment and thus effectually intercept any 

 wash that may occur from this cause or from the 

 accidental overspill of the dam due to extraor- 

 dinary floods or carelessness in handling ^he waste 

 ^ates. Such a device as this would have saved 

 the dam that caused the Johnstown disaster and 

 many others which have gone out under similar 

 conditions. 



It mu'st not be hastily inferred that the Hollow 

 Core Wall increases the cost of the dam. The 

 chances are that it actually decreases it. This is 

 too broad a subject to discuss in an advertisement, 

 but it will be fully amplified in our circular on 

 EARTH DAMS which we will send on applica- 

 tion. 



There is a modification of the Hollow Core 

 Wall which relates particularly to Hydraulic Fill 

 Dams and will be made the subject of our next 

 advertisement. 



A' 



''- 



Engineer Constructors 

 FIGURE 3. Earth Dam at Altoona, Pa., showing effect of wash. 88 Pearl St., BOSTON, MASS. 



Respectfully submitted, 



Ambursen Hydraulic Construction Co. 



All Inquiries from Canada, should be addressed to AMBURSEN HYDRAULIC CONSTRUCTION CO. OF CANADA, Ltd. 405 Dorchester St. W. Montreal 



When writing to advertisers please mention The Irrigation Age. 



