BUILDING 169 



power is higher due to their greater friction. They may also 

 be made of larger diameters than can be obtained with wood piles, 

 and a less number is therefore required to support a given load. 



When designing foundations the first step is to ascertain the 

 total weight that will be sustained by the soil and then to pro- 

 vide a sufficient number of square feet of area of the base to bring 

 the pressure per square foot within the safe value. The weight 

 should include the machines, fittings, the weight of the founda- 

 tion itself, and, in the case of the turbines, the weight due to the 

 water thrust unless this is balanced. Separate foundation should 

 be provided for the different units so as to isolate any failure as 

 far as possible. 



Concrete is always used for the foundations. They should 

 be solid for the machinery, while the building may be supported 

 on columns or arches so as to economize on the concrete. Where 

 there is danger of high water in the tailrace, the outside founda- 

 tion walls should necessarily be made water-tight so as to prevent 

 water from entering and flooding the basement. For such cases a 

 sump is, therefore, generally provided into which the seepage 

 may collect and from where it can readily be pumped out. A mix- 

 ture of one part cement, three parts sand and six parts gravel 

 or broken stone forms a concrete that is extensively used, and 

 which has given perfect satisfaction for machine foundations. 



On small machines the foundation bolts and plates may be 

 placed in position before the concrete is put in. They should be 

 hung in place by a wooden template and the bolts surrounded by 

 stove pipe, conveyor pipe, or scrap-iron pipe, several inches larger 

 than the bolts themselves. This allows for mistakes in location 

 and variation in the machine parts, the holes being filled when the 

 base is grouted. With large machines, however, it is better to 

 have pockets in the concrete large enough for the foundation plates 

 to be dropped in. These holes can be filled in, grouting the 

 base, and serve the further purpose of making a good bond between 

 the foundation proper and the grout in and under the base. 



Grout is preferable mixed half sharp clean sand and half cement. 

 It should be thin enough to flow readily and should be well pud- 

 dled into place. Before pouring, all dust and trash should be 

 cleaned off and the foundation thoroughly wet down. It is better 

 to use a fairly slow-setting cement on large castings. In some 

 cases cement for grouting has been set aside and aged a year 



