64 BULLETIN 463, U. S. DEPARTMENT OF AGRICULTURE. 
or spongy material which will not compact under the roller * so as to make a 
firm unyielding subgrade or earth road surface. 
All trees, stumps, and roots within the limits of the improvement shall be 
grubbed up so that no part of them shall be within 6 inches of the surface of 
the ground or within 18 inches of the surface of the subgrade, except that if 
they occur in an area to be covered by a fill more than 18 inches in depth they 
shall be grubbed up or cut off even with the present surface of the ground. 
Embankments shall be formed of good sound earth or stone and carried up 
full width. The material shall be deposited in layers not more than 1 foot 
in thickness, and each layer shall be rolled * until thoroughly compacted with 
a roller weighing not less than 10 tons. All existing slopes and surfaces of 
embankments shall be plowed or scarified where additional fill is to be made, 
in order that the old and new material may bond together. When sufficient 
material is not available within the right of way to complete the embankments, 
suitable borrow pits from which the contractor must obtain the necessary 
material will be designated by the engineer. If there is more material taken 
from the cuts than is required to construct the embankments, as shown on 
the plans, the excess material shall be used in uniformly widening the em- 
bankments or shall be deposited where the engineer may direct. Where 
embankments are formed of stone, the material shall be carefully placed so 
that all large stones shall be well distributed and the interstices shall be 
completely filled with smaller stone, earth, sand, or gravel, so as to form a solid 
embankment. 
During the work of grading the sides of the road shall be kept lower than 
the center and the surface maintained in condition for adequate drainage. 
The grading of any portion of the road shall be complete before any surfac- 
ing material is placed on that portion, and where the plans do not call for any 
substantial change in the grade of any existing section of the road, the surface 
shall be completely scarified to a depth of 3 inches or more before the subgrade 
is prepared. 
All excavated material 2 will be classed as earth and rock. Only rock in 
place which requires blasting for its removal and bowlders of one-half cubic 
yard or more in volume will be classed as rock excavation. 
Materials obtained from excavation and used in embankments will be paid 
for as excavation only, though the contractor is required to shape and trim 
the embankments properly. Materials obtained from excavation and used for 
surfacing will be paid for only once and at the price bid for surfacing 
material. 
Quantities of materials moved in grading will be measured in excavation 
and the volumes determined by the average end-area method, and no payment 
will be made for materials excavated outside the slope lines shown on the 
plans unless the additional excavation is ordered by the engineer. 
The contract prices for excavation shall be compensation in full for all the 
work which is required to be done under the heading " grading," except that 
an additional allowance at the rate of 1£ cents per cubic yard per 100 feet 
will be made for all materials of excavation necessarily hauled more than 500 
feet. The centers of gravities of cuts and corresponding embankments will 
be used in determining the length of haul, and if the center of gravity of the 
1 For earth and sand-clay arods the rolling is frequently omitted. 
2 In general it is more satisfactory to classify the materials of excavation and to invite 
unit-price bids rather than lump-sum bids. However, if unit-price bids are invited it is 
important that the various quantities be accurately determined in order that the best bid 
may be selected. If lump-sum bids are desired, omit the following paragraphs. 
