258 PARKS 



2. Sub grading for Walks. 



(a) Brick, tile, concrete, macadam, gravel, cobblestone and medina block. 

 The subgrade should be completed to an even sloping surface as required 

 for subsurface drainage (figures 1-4, Plate 107) and at the required depth 

 below the proposed finished grade of the walk. In sandy soils the surface 

 of the subgrade should be parallel with the finished grade of the walk sur- 

 face, no drain being required. 



Where frost action extends deep into the ground, especially in clay 

 soils, careful attention must be devoted to the proper drainage of the sub- 

 grade, which subgrade should slope from either side of the walk (]/ 2 to ^ 

 inch per foot) toward the middle line in order to remove quickly any sub- 

 soil water which may find its way into the area under the walk surface. 

 This is especially important in the construction of all types of walks included 

 in this group, particularly those with a definite paved surface, the heaving 

 of which through frost action causes serious injury. 



(b) Tanbark walks (subgrading). Tanbark walks constructed on a 

 sand-loam soil require no subgrading other than that necessary to procure 

 the desired surface. Tanbark walks constructed on a gravel foundation, 

 especially in a clay soil, require the same solution as that outlined above 

 under za (subgrading for walks). 



(c) Turf walks and woodland trails (subgrading). Woodland trails 

 require little or no subgrading other than that necessary to develop the 

 desired surface. The subgrading of turf walks requires the same careful 

 work, for the best results, as that outlined under la. 



(d) Stepping-stone walks (subgrading). The subgrading of the area 

 under a stepping-stone walk presents the same problem as that outlined 

 under 2a with the exception that when the stepping-stones are spaced at 

 a considerable interval it is not necessary to finish the surface of the sub- 

 grade to meet any drainage requirements. If the stepping-stones are placed 

 at closer intervals, making it necessary to excavate and to subgrade a con- 

 tinuous area under the line of stepping-stones, then provision should be 

 made for proper subsurface drainage. 



(e) Board walks (subgrading). The problem of subgrading the area on 

 which board walks are to be constructed involves only the work of making 

 a proper subgrade on t.he desired profile as a foundation on which the 

 board walk surface is to be constructed. 



3. Drainage (General Considerations). 



(a) Brick, tile, concrete, macadam, gravel, cobblestone and medina block. 

 The surface of the subgrade should be so finished that all ground water 

 will readily drain away. The presence of excessive quantities of water in 



