Agenda - Council - 06/27/2017 - Laserfiche WebLink

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az) Riverdale Drive Improvements Ramsey, Minnesota NTI Project No. 15.61197.100 All import fill should generally consist of non -organic debris free soils of similar composition to the in place native soils. All import fill soils should be approved by NTI or the City's representative prior to utilization. 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 side slopes 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). PAVEMENT RECOMMENDATIONS The most conservative method of subgrade preparation would be remove the undocumented fill soils and replace them 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 relatively a -typical considering the relative uniformity of the subgrade soils encountered within the soil borings. If the City is willing to accept some risk in regard to the future pavement performance, NTI recommends that prior to installing the aggregate base that the existing subgrade be scarified and re -compacted to a depth of at least 12 inches. A proof roll test should then be performed to determine soft or unstable subgrade areas. If rutting or localized unstable subgrade areas are observed, those areas should be subcut, moisture -conditioned, and re -compacted or removed to a stable depth. Excavations for soil corrections in paved areas should allow for a 2 foot oversize beyond the edges of the pavement. The proof roll should be performed with a tandem axle dump truck loaded to gross capacity (at least 20 tons). Acceptance criteria of the proof roll shall be limited to rut formation no more than one inch depth (front or rear axles) and no pumping (rolling) observed during the visual inspection. Proof roll tests should be observed by an experienced technician or geotechnical engineer prior to placement of the aggregate base course to verify the subgrade will provide adequate pavement support. If imported fill is required in paved areas it should consist of debris free, non -organic, mineral soil similar in composition to the subgrade soils encountered in the surrounding areas. If sand is imported into areas that are underlain by relatively impervious fine grained soils the sand layer should be drained with drain tile in order to prevent frost heave from water trapped within the imported sand layer during freezing temperatures. Similarly, if clay is used in conjunction with lane widening, drainage from any existing granular soils may be impeded unless subsurface drainage is included. Individual lifts of engineered fill should be tempered for moisture content, placed and compacted as noted in the "Placement and Compaction of Engineered Fill" section in Appendix B of this report. MINIMUM PAVEMENT THICKNESS Estimates of minimum thicknesses for new pavement sections for this project have been based on the procedures outlined in the MnDOT Pavement Design Manual using soil parameters based on soil types. Page 3 of 14