02/09/23 - Laserfiche WebLink

Home

Report of Geotechnical Exploration West Armstrong Redevelopment Area, Ramsey, Minnesota March 30, 2022 AET Report No. P-0004952 AMERIAN ENGINEERING TESTING minimum compaction level of 95% of the standard maximum dry unit weight can be used below the critical subgrade zone. 6.4 Design R-Value Based on the subgrade preparation recommendations presented herein, the pavement section (bituminous and aggregate base layers) can be designed based on an R-value of 50. 6.5 Utilities Based on the conditions encountered at the boring locations, we judge the inorganic soils to be suitable to provide adequate support for utility construction. If silty soils are present at the trench bottom, a 4-inch thick Granular Bedding (MnDOT Specification 3149.F) layer should be placed beneath the pipe to improve support uniformity. We also recommend the removal of any cobbles/boulders in the trench bottoms prior to utility installation. This will reduce the potential for the development of point loads on the pipe that would not be accounted for in the pipe design. Please refer to the attached standard sheet entitled "Utility Excavation Backfilling" and "Bedding/Foundation Support of Buried Pipe" for additional details regarding utility bedding and utility backfilling. 6.5.1 Trench Backfill The excavated non -organic soils can be used as backfill for the new utility trenches. Excavated organic soils should not be used as backfill below the roadway. Review of our borings indicates that the trench backfill will primarily consist of sands with silt and sands. These types of soils are generally not considered corrosive. We recommend that bedding be placed uniformly around the pipe to avoid having dissimilar materials touch the pipe that could set up corrosion cells. In our opinion, all metallic utilities should be coated or wrapped. Utility trench backfill should be placed per the requirements of MnDOT Specification 2106.3G.1 (Specified Density Method). The backfill soils should be placed in a maximum lift thickness of 1 foot or less for the granular soils and 8 inches or less for the cohesive soils. This specification requires all backfill soils placed within an excavation trench be compacted to a minimum of 100% of the standard maximum dry unit weight defined in ASTM: D698 (Standard Proctor test). Consideration can be given to modifying the project specifications to allow for a reduced minimum compaction level of 95% of the standard maximum dry unit weight to be used below the critical subgrade zone. Backfill soils placed in the upper 3 feet of the subgrade should be compacted at a water content between 65% to 102% of the standard optimum water content. Page 5 of 7