DRAINAGE METHODS FOR COUNTY ROADS. 59 
but very quick bonding and satisfactory gravel. The soil was poor, 
being a micaceous clay, and the base was laid in two courses, with 
the first thoroughly harrowed to shake the finest to the bottom and 
close the foundation against the clay. No effort was made to close 
the top foundation course as the gravel topping served adequately 
to do this. 
Figure 15 shows a typical cross section for a crushed-stone foun- 
dation and indicates the limiting dimensions used in good practice. 
The proper manner of spreading and compacting the stone prob- 
ably can best be described by stating certain precautions it is neces- 
sary to observe in order to secure satisfactory results. In doing 
this it will be necessary to repeat several of the precautions already 
mentioned as being applicable to gravel foundations, because the 
two types of construction are very similar in many respects. In fact, 
where the gravel used is such as to compact readily without the pres- 
ence of clay the construction methods are practically the same as 
when crushed stone is used. 
1. The first precaution in constructing a crushed-stone or any other type of 
foundation, of course, is to see that the subgrade is well prepared of good 
material and that it is firm at the time the stone is spread. 
2. The stone should be delivered in vehicles adapted to spreading it out in a 
uniform layer to the required loose depth. If such vehicles are not available, 
the stone should be dumped on platforms and spread to the required depth with 
hand shovels. This requirement is of especial importance because it is prac- 
tically impossible to secure a uniformly compacted foundation unless some such 
method is followed. Where whole loads are dumped on successive spots of the 
subgrade and spread by merely raking off the tops of the piles thus formed, a 
dense core will be formed where each load is dumped and the area between 
cores will be much less dense. When the layer of stone is rolled, the roller 
will tend to ride on the cores with the evident result that the foundation will 
iiot be uniformly compacted and while its appearance may be satisfactory when 
first completed, lack or uniform density is almost certain to result later in 
irregularities, and these will continue to occur long after completion of the top 
or wearing course. 
3. If in hauling and spreading the stone, the fine and coarse particles be- 
come more or less separated, as frequently is the case, each layer of the founda- 
tion should be harrowed with a tooth harrow until the different sized particles 
are distributed uniformly throughout the mass. When moderate care is used in 
handling the stone harrowing should not generally be necessary, though with 
some varieties of stone there seems to be a strong tendency for the dust and 
fine particles to become segregated while the material is being loaded into 
vehicles and in such cases harrowing may be very desirable. 
4. After each layer of the stone is spread, and harrowed if necessary, it should 
be rolled with a power roller weighing about 10 tons, until it is thoroughly and 
uniformly compacted. The rolling should begin preferably at the edges of the 
road and progress toward the center, and should continue until no appreciable 
settlement is caused by additional rolling. 
5. In general, the voids in the top layer of the foundation should be filled 
by spreading coarse sand or stone screenings over this layer while the rolling is 
in progress. With some varieties of rather brittle stone the voids may be filled 
