PROCEEDINGS OF SECTION J. 739 
10.—CONSTRUCTION AND MAINTENANCE OF 
METALLED ROADS. 
By Wiuiam Bace, M.C.E. 
| Abstract. | 
In deciding what construction to adopt, one must consider the 
nature and extent of the traffic upon a road. ~What is required, 
in addition to a good route and easy gradients, is a smooth 
surface, sound enough to carry the traffic, and one that can be 
made and maintained at the least ultimate cost. Where traffic is 
light the natural surface may answer, or by small expense in 
drainage and formation may be made to answer; as the traffic 
increases, 1t may be necessary to use selected local materials to 
cover the formation ; and, where this is not sufficient, to metal. 
As traftic becomes heavier, repairs and renewals become more 
frequent, until the metalled surface no longer satisfies the require- 
ment of a smooth surface, the traflic being frequently harassed 
during the progress of repairs, and the ultimate cost comes to 
exceed that of a more permanent road, such as stone, hardwood, 
or asphalt paving upon a concrete foundation. 
In constructing a metalled road, the bed below the road should 
be sufficiently sound to bear the traftic without sinking, and can 
generally be made so by draining and consolidating with roller, 
or otherwise, before putting on the bed-metal. Where soft clay 
or sand is met with, a layer of loam or turf, or even cut scrub, is 
often sufficient to prevent it working up into the metal bed. It 
is not an uncommon practice to cover sand with clay, but it makes 
a very objectionable foundation. Sand itself is a good founda- 
tion. It should be prevented from working up into the metal 
from below, and the borders should be covered to prevent it 
drifting on to the surface of the metal. The same curvature 
should be given to the bed as you give to the finished surface of 
the roadway ; a slope of about 1 in 30 from the edges is generally 
sufficient, and the same slope should be given to the border, if 
any, between the metal and the channel or water-table. 
The bed-metal, when properly laid and consolidated, should be 
permanent and require no maintenance; its duty is to act as a 
foundation to bear and distribute the weight of the traffic. It 
need not be of so hard a stone as the surface-metal, and is usually 
broken to a larger gauge—3}-inch and 4-inch metal is very 
commonly used, but a smaller size is better. It should be well 
rolled when spread. The depth depends upon the nature of the 
traffic and the soundness of the bed, but 5 inches is deep enough 
in most cases. If schist or other soft stone be used it consoli- 
dates more rapidly. Good schist metal is being extensively used 
for bed-metal in many of our suburban streets, and gives very 
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