CONSTRUCTION NOTES 259 



the subsoil under such walks will involve injuries on account of frost action. 

 Drainage may be provided by tile or blind drains extending under the 

 middle line of the walk and located as shown in figures 14, Plate 107, 

 with proper outlets. The outlets from the four-inch tile drains should be 

 at sufficiently frequent intervals to remove the ground water into larger 

 drainage lines before these smaller pipes are loaded beyond their capacity. 

 The trenches in which any drainage lines are installed should be of a mini- 

 mum width and have a depth of six to twelve inches below the finished 

 subgrade for the walk. If such walks are constructed upon a soil which is 

 porous and has ample subdrainage to keep the ground water at a depth 

 below the frost line, then the installation of drainage lines under the walk 

 surfaces is unnecessary. 



On any of the above walks with a well-defined hard surface it is neces- 

 sary to provide a slight transverse grade, approximating one-fourth inch 

 per foot (figure 4, Plate 112), to the surface of the walk in order readily to 

 remove the surface water during heavy rainfall. This is especially true if 

 the walk is constructed on a more or less level grade or is used intensively 

 as a public walk. 



On all garden walks of whatever character it is quite necessary that 

 the surface drainage problem of the walk area itself and of the surrounding 

 area should be given careful study and that inlets (see figures 5 and 6, 

 Plate in) should be installed at the proper locations to remove this surplus 

 surface water in the shortest possible time. The surface grades should be so 

 studied that the surface water will readily flow to these inlet locations. 

 Wherever any walk is constructed on a steep grade, especially in a cut or 

 on the side of a slope (see figure 5, Plate 112) where the surface water 

 during storms will naturally follow the line of the walk, definite gratings 

 (see figure 7, Plate in) should be installed, especially at the top of any 

 steps or at sufficiently frequent intervals along the length of the walk to 

 remove the surplus surface water before it annoys those using the walk or 

 causes injury to the walk and the surrounding area. As a general practice it 

 is desirable to have the finished surface of the walk slightly above the sur- 

 rounding area on either side. On macadam walks and gravel walks it is quite 

 essential that this surface water should be removed at much more frequent 

 intervals than on brick, tile or concrete walks. Wherever walks are constructed 

 parallel to a well-defined slope there should be, if practicable, a very definite 

 sod or other type of gutter on the uphill side of the walk, provided with 

 catch basins at frequent intervals to remove the surface drainage coming 

 from the slope before this surface drainage has an opportunity to flood the 

 walk and cause serious damage. 



(b) Tanbark walks (drainage). The same principles of drainage as are 



