DRIVES, AVENUES, AND SERVICE ROADS. 



the steeper one, the surface of the drive will appear to be raised too high at the point 

 of junction. The remedy is to plot all the gradients on to the sections in swinging curves 

 at their junctions, at the same time keeping changes in both direction and gradient as 



few as possible. The accompanying sketch (111. 

 No. 88) shows, by full lines, the engineer's methods 

 in the bottom of a hollow and, by dotted lines, 

 how the Landscape Architect would alter them. 



FIG. oo. 



Probably the most effective curved drive ever 



designed by the author was one something under half a mile in extent which, for its whole 

 length, was carried in one long simple sweep round an amphitheatre of hillside and rising 

 at one gradient the whole way from the entrance gates to the forecourt of the house. 



The railway engineer's methods of working his sections will also need adaptation to 

 the special requirements of private road work. The best way is to take a line of levels 

 along the centre of the proposed route, and at each point measured, to take a level 

 on either side, say fifteen feet away to right and left. The three lines of levels thus 

 obtained are all superimposed over one datum line in three different coloured inks, making 

 the centre line the most prominent to ensure clearness. This method, of course, causes 

 a little distortion in the lengths of the side sections on the curved portions of the drive 

 as they are represented as being a little longer than they are on the inside of a curve, 

 and are shortened on the convex side of the bend. This, however, can easily be allowed 

 for in calculating the proportions of cutting and filling. It has the advantage of 

 showing the cross-grading at every point at a glance without reference to the cross 

 sections usually prepared in such cases. 



The writer's own method is to plot the three superimposed sections to a much larger 

 vertical than horizontal scale, and then to add the centre line only, drawn to the same 

 scale as the horizontal measurements, using the same lines of heights above the datum. 

 The arrangement of the surface levels can then be proceeded with on the upper set of 

 lines, and are afterwards transferred to the lower centre line as a check, from which the 

 resulting gradients can be read without calculation. The amount of cutting or filling 

 at any point can, of course, be more accurately computed from the higher set of lines. 



Where the subsoil is of such a nature that all the roadmaking materials can be 

 obtained in making the excavated portion of the drive, the finished level should be plotted 

 on to the sections, but where these will have to be carted from a distance, the found- 

 ation levels should be laid down, thus allowing an equal amount of cutting and filling. 

 It would seem, at first sight, as though rather more filling than cutting would be 

 necessary, as the material used for filling packs so much more loosely than before being 

 disturbed, even when it has had time to settle solid, but the amount used in making 

 up the banks on the low side of a cross slope will just about absorb the surplus in 

 all ordinary cases. 



Ease of As to gradients, these should always be as easy as possible. The sight of horses 



gradient. struggling up a steep drive is not conducive to that sense of repose which it is the 

 first object of the garden designer to obtain, and even in the case of a motor-car, slow 

 threshing uphill on the lowest gear tends to be irritating. 



As a general rule, gradients of more than one in twelve are to be avoided, though 

 the whole question is relative to the general contours of the district. What is the best 

 possible in one place would be distinctly bad in another. In extreme instances in the 

 English Lake District, where the residence may be placed in an almost inaccessible 

 position for the sake of a unique view, the writer has occasionally been compelled to 

 adopt a gradient of one in six-and-a-half or seven for short distances. This may be 

 taken as being the steepest slope up which it is possible to get a heavy luggage cart or 

 other loaded vehicle. 



76 



