Agenda - Council - 01/08/2019 - Laserfiche WebLink

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Brookview Estates Reconstruction Ramsey, Minnesota NTI Project No. 18.MSP06855.000 2.3 Utilities The fill and native soils observed in soil borings were generally suitable for utility support. Due to the observed groundwater levels and depending on the installation depth of the utilities, temporary dewatering would likely be required during the utility trench excavations for deeper utilities, such as sanitary sewer. Stabilization of the trench subgrade may be required, in particular in locations with lean clay subgrade, in order to provide a stable platform for construction. Stabilization could consist of a one half to one foot layer of crushed rock or sand with a maximum 5 percent material passing the No. 200 sieve and 50 percent passing the No. 40 sieve. The Geotechnical Engineer of Record or their designated representative should observe the project excavations to determine that unsuitable materials have been properly removed and adequate bearing support is provided by the exposed soils. The exposed soil at the base should be compacted with a vibratory roller to 95 percent standard Proctor dry density (ASTM D698). Such observations and testing should be performed prior to backfilling. The on -site, non -organic soils are anticipated to be suitable for reuse if properly moisture conditioned and compacted. Replacement backfill required in utility trenches should consist of non -organic material similar to the surrounding soil. All import fill should be approved by NTI or the City's representative. It is especially important that trench backfill for utility construction within paved areas be thoroughly compacted to minimize future pavement damage. We recommend that such soils be compacted in accordance with the recommendations noted in the "Placement and Compaction of Engineered Fill" section in Appendix B of this report. The stability of embankments along utility excavations is dependent on soil strength, site geometry, moisture content, and any surcharge load for excavated soils and equipment. We present cautionary remarks concerning stability of excavation sideslopes in the "Excavation Stability" section of this report. The Contractor is solely responsible for assessing the stability of and executing underground utility and project excavations using safe methods. The contractor is also responsible for naming the "competent individual" as per Subpart P of 29 CFR 1926.6 (Federal Register - OSHA). 2.4 Pavement Recommendations Full Reconstruction Option The most conservative method of subgrade preparation would be to remove the undocumented fill soils and replace them in their entirety with properly compacted engineered fill. This method of subgrade preparation would provide the most uniform subgrade but would also be the most costly method of construction and would be a relatively a -typical method of subgrade preparation for improvements to existing municipal roadways. If the City were willing to accept some risk in potential long term increased maintenance of the pavement section for the significant upfront savings, the roadway can be reconstructed over the existing fill. Page 3 of 7