Res. #15-036 - Approving Plans & Specs. & Ordering Ad. For Bids

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City of Centerville Project SP-07-03738 November 29,2007 Page 11 DA.c. Design Sections--Pavement Lifespan The City Standard for residential roadways within City of Centerville is 3 1/2 inches bituminous(1 112 inches wear course over 2 inches of base course)and 8 inches of aggregate base over 20 inches Select Granular Borrow(subbase layer) Assuming that pavement subgrades will ultimately consist of compacted materials exhibiting an R-value of at least 12,and the traffic loads indicated in Section C.1,it is our opinion that the pavement section required by the City of Centerville will be adequate for a 20-year lifespan. DA.d. Materials and Compaction We recommend specifying crushed aggregate base meeting the requirements of Minnesota Department of Transportation(Mn/DOT)Specification 3138 for Class 5. We recommend that the bituminous wear and base courses meet the requirements of Specifications 2360, Type LV. For areas that will experience traffic loads anticipated to be more then 1,000,000 LSALs over a 20-year life span,we recommend that the wear and base courses meet the requirement for Type MV. We recommend the aggregate gradations for the base course asphalt meet Gradation Number 3.We recommend the aggregate gradations for the wear course asphalt meet Gradation Number 3 or 4. Since Gradation 4 has a smaller maximum particle size than Gradation 3,it is typically preferred for use in wear courses for aesthetic and textural considerations. We recommend using one of the following three Performance Graded Asphalt cements: PG 64-28,PG 58-28 or PG 64-22. PG 64-28 is most commonly recommended for use in the Twin Cities Metro area, and of the three is least susceptible to rutting during warm periods(summer)and shrinkage cracking during cold periods(winter). PG 64-22 is most commonly recommended for use in the southern portion of the state,and PG 58-28 is most commonly recommended for use in the northern portion of the state Although PG 64-22 and PG 58-28 are generally less expensive than the preferred PG 64-28,it should be noted that their use can lead to increased maintenance costs(crack sealing). We recommend that the aggregate base be compacted to a minimum of 100 percent of the standard Proctor maximum dry density. We recommend that the asphaltic concrete pavement be compacted to an minimum density of 92 percent of the maximum theoretical density. DA.e. Subgrade Drainage The 4-inch perforated PVC pipes should be wrapped with a filter fabric to reduce the potential of the fine-grained soils migrating into the pipe and clogging the holes. The drain tile piping should terminate at the storm sewer catch basins or manholes. Where possible,the pavement subgrade should slope towards the drainage pipe to promote water movement to the drain tile.