§ 153.120  SUBGRADES.
   (A)   Existing topsoil shall be removed from the area of proposed street pavement plus two feet outside the proposed back of curb. Removal shall be to a depth as necessary to remove all organic material or ten inches, whichever is greater.
   (B)   Street subgrades shall be compacted to not less than 95% of the standard laboratory density in accordance with the applicable section of the Standard Specifications for Road and Bridge Construction, IDOT.
   (C)   The street pavement subgrade shall have sufficient stability to accommodate construction traffic without excessive subgrade rutting or shoving. Prior to commencement of pavement construction, the in-situ subgrade shall have a California Bearing Ratio (CBR) of at least 6% in the top 12 inches of subgrade, provided that the subgrade is within one-tenth of a foot of final grade.
   (D)   The CBR percentage will be ascertained by the subdivider’s engineer by use of a dynamic cone penetrometer (DCP) with one test every 100 feet of roadway, with tests alternating between the two traffic lanes (i.e., 200-foot test intervals in each lane of traffic). The DCP test shall also be conducted to a depth of at least two feet below the finished grade of the subgrade to provide the subdivider’s engineer with knowledge of the stability of the underlying soil.
   (E)   The rate of penetration shall be measured and correlated to CBR using the relationship shown on the attached graph.
   (F)   Areas of subgrade that are changed in elevation by more than three inches after acceptance testing must be retested once final grade in achieved. Subgrades which are subjected to a freeze-thaw cycle prior to paving must be retested.
   (G)   The suitability of all subgrades shall be tested via “proof-rolling” with a loaded tandem truck. Any soft subgrade areas which show rutting, cracking, or rolling shall be reconditioned to provide a firm, suitable subgrade.
   (H)   Any areas of street pavement subgrade which fail to meet or exceed the DCP testing requirements or fail the proof-rolling test shall be remedied to achieve the required stability. Acceptable methods of remediation shall include but not be limited to aeration and recompaction, undercut and backfill, and lime treatment. The remedied areas must be retested and meet or exceed the DCP stability requirements. Streets which do not meet the minimum subgrade compaction requirements will not be accepted.
(Ord. 97-7, passed 7-1-1997, § 5.14.6)