CONSTRUCTION NOTES 279 



gravity walls as in Plate 115, page 278). (2) Free-standing walls (of stone 

 masonry, brick masonry, stucco on hollow tile and stucco on expanded metal, 

 as in Plate 117, page 282, and, partly free-standing, in Plate 117, figures 4 

 and 4<a). A retaining wall must be so constructed that it will have adequate 

 stability to resist the lateral pressure from the supported bank of earth. A 

 free-standing wall differs from a retaining wall in that it is usually faced on 

 both sides (see Plate 117) and there is no lateral pressure which would tend 

 to overturn it. In the construction of all walls it is very important that 

 the correct lines and grades should be carefully established, and this is 

 especially important with reference to retaining walls where a small error 

 in elevation may cause greatly increased construction cost. 



Foundations for walls. The foundation is one of the most important 

 factors to be considered in the construction of any wall. It is doubly impor- 

 tant that the foundation for all concrete or masonry walls (see Plate 116, 

 and Plate 115, except figure 2) should rest upon a well-drained and solid 

 natural subsoil. Any settlement in a wall of this kind may cause serious 

 damage. A similar settlement because of faulty foundation under dry stone 

 walls (see Plate 115, figure 2) may not be as serious and may be more easily 

 repaired. All walls on the top of which a balustrade or iron grill is to be 

 erected should have the most secure type of foundation. The bottom of 

 the foundation under all walls with the exception of dry stone walls (Plate 



115, figures 2, 3 and 4) should be below the line of normal frost action. 

 No foundation should be constructed for any type of wall upon subsoil 

 which is not thoroughly compacted. Where frost action is a negligible 

 factor the problem of constructing walls is very much simplified. It is only 

 necessary to extend the foundation to a depth where a firm natural sub- 

 soil is encountered. It is desirable to provide drainage in heavy clay soils 

 and especially to install weep-holes which will prevent free soil water from 

 accumulating at the back of the wall. 



Retaining Walls. 



(a) Reinforced concrete. The foundation for any reinforced concrete 

 wall should be of concrete properly designed in accordance with standard 

 practice for walls of various heights retaining different kinds of soil. The 

 foundation or footing should have approximately the form shown in Plate 



1 1 6, figures i and 2. In the construction of this type of wall it is customary 

 to pour the concrete (1:2:4 mixture) for the footings after the forms for the 

 footing and a portion of the vertical steel, with the necessary supports, is 

 in place. Because of the great strength required in a reinforced cantilever 

 wall it is very necessary that the steel should be carefully computed and 

 placed in accordance with definite calculations. 



