§ 2. Grading.

A.

Unclassified excavations: This classification consists of all roadway and drainage excavation, regardless of the nature of the material or the manner in which it is removed. It includes removal and disposal of unsuitable or unstable material under the roadbed section, and backfilling with suitable materials.

1.

Rock, boulders: All rock and boulders in the roadbed shall be excavated to a depth of at least 12 inches below the subgrade and the space backfilled to the correct grade with material suitable as subgrade.

2.

Removal of unsuitable or unstable materials. Where materials unsuitable for foundation or roadway purposes occur within the limits of the roadbed and front slopes, the contractor shall excavate and remove such materials to the bottom of their depth.

B.

Backfills for culverts and pipe: The backfill around and over culverts and minor structures shall be of selected material class I or II. The backfill shall be placed and compacted so as to avoid unbalanced loading and to avoid placing undue stress on the structure. Backfills shall be built up in horizontal layers not more than six inches thick, and each layer shall be thoroughly compacted by the use of rapid-striking mechanical tampers or hand tampers. After compaction, the dry weight per cubic foot for each layer of backfill shall be at least 95 percent of the maximum laboratory dry weight per cubic foot.

Backfills shall be built up and compacted above pipe and arch culverts to a thickness of at least two feet, or one-half the vertical inside diameter of the pipe, whichever is greater, unless these dimensions exceed the proposed height of the embankment, in which case the backfill shall be made and compacted to the height of the embankment.

Before any backfilling is begun, the city engineer will be notified for an inspection.

C.

Embankment:

1.

Preparation for embankments:

a.

Depressions: All depressions below the ground surface containing water shall be filled with suitable material and compacted to the ground surface before the embankment proper is begun.

b.

Scarification and other preparation: The entire area upon which the embankment is to be placed shall be plowed, scarified and finely broken up to a depth of at least six inches and all cleavage planes shall be destroyed before the embankment is begun.

2.

Embankment formation: In general, embankments shall be constructed as shown in this paragraph, but the construction will vary with the various classes of soil as indicated in the succeeding paragraphs. The material shall be deposited and spread in uniform horizontal layers not more than six inches thick, loose measurement, for the full width of the cross-sections, and these layers shall be kept level by the use of graders, bulldozers or other approved equipment.

a.

Moisture content: Each layer shall be compacted at a moisture content proper to permit the compaction specified below. Material containing too much water shall be dried to the correct moisture content. If the material is too dry, water shall be added and uniformly mixed with the soil before it is compacted.

b.

Degree of compaction: The top 12 inches of embankment shall be compacted to at least 100 percent of the maximum laboratory dry density. Embankment material located between one foot and six feet below the top of the embankment shall be compacted to at least 90 percent of the maximum laboratory dry density. The measurement of depth as described above shall begin at an elevation equal to the bottom of subgrade treatment material is used.