Agenda - Council - 10/26/2021 - Laserfiche WebLink

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Dewatering Ground water was encountered in 5 of the soil borings at depths of about 81/2 to 14 feet below the ground surface. With pipe inverts anticipated to bear about 7 to 10 feet below the ground surface there is the potential that groundwater could be encountered during spot utility repairs and dewatering could be required. Where dewatering is required, we recommend the groundwater level be temporarily lowered to a minimum of 2 feet below the lowest anticipated excavation elevation to allow for construction. In sand soils we do not recommend attempting to dewater from within the excavation. Upward seepage will loosen and disturb the excavation, resulting in a "quick condition". Rather, we recommend groundwater be drawn down below the anticipated excavation bottom. 4.4 Pavement Recommendations The City of Ramsey may have standard plates that dictate bituminous pavement design. If so, we assume the pavements be designed in accordance with the appropriate standard plates. The following paragraphs provide general pavement recommendations in the absence of standard plates. Reconstruction In areas that will be reconstructed we recommend removing all vegetation and topsoil, if any, and all pavements, aggregate base, organic soils and any soft or otherwise unsuitable materials from beneath the pavement subgrade. Prior to placing the aggregate base (Class 5) we recommend compacting the subgrade soils to provide a more uniform surface and to identify soft, weak, loose or unstable areas that may require additional subcuts. Backfill, if needed, to attain pavement subgrade elevation can consist of any mineral soil provided it is free of organic material or other deleterious materials but recommend additional fill, if needed, consist of sandy soils similar to the on -site materials. Granular fill classified as SP or SP-SM should be placed within 65 percent to 105 percent of its optimum moisture content as determined by the standard Proctor. Other fill soils should be placed with moisture contents within a range of 1 percentage point below and 3 percentage points above its optimum moisture content. The upper 3 feet of fill and backfill should be compacted to a minimum of 100 percent of its standard Proctor maximum dry density. Full Depth Reclamation For "Full Depth Reclamation" areas there may be instances where the recommended aggregate base thickness exceeds the existing aggregate base thickness. The preferred method of pavement repair would be to reclaim the existing bituminous, subcut the subgrade, replace the reclaim and add additional aggregate base as needed then construct the bituminous pavement. Subcutting the subgrade may not be feasible or cost effective. As an alternate it may be possible to use a thicker bituminous pavement along with the existing aggregate base or possibly subcutting some of the existing aggregate base. Using MN/DOT granular equivalencies, one (1) inch of bituminous is equivalent to 2.25 inches of MN/DOT Class 5 aggregate base. R-Values Laboratory tests to determine the soils Hveem Stabilometer R-Value (R-Vaiue) was beyond the scope of this project. Information provided in the State of Minnesota Department of Transportation, Geotechnical & Pavement Manual, Part II, indicates that R-Values for granular materials meeting the ASTM Classification SP or SP-SM can range from 50 to 70. It is our opinion that an R-Value of 50 can be used for pavement design. 9