Agenda - Council - 09/12/2017 - Laserfiche WebLink

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iso Engineered Fill and Winter Construction Sunwood Drive — Street Improvements Ramsey, Minnesota NTI Project No. 16.61770.100 The silty sand soils on this site will be susceptible to frost action if not provided adequate drainage, insulation or coverage. Frozen soil should not be used as backfill. When the ambient air temperature falls below freezing for an extended period of time, frost forms, and soil near the surface grade expands. Settlement of the fill may occur as the frozen soils thaw. If frost penetrates the soil prior to paving, soils must be thawed, scarified, and re -compacted as recommended in this report. Subgrade soils should be inspected prior to paving to verify frozen conditions are not present. PAVEMENT RECOMMENDATIONS Mill and Overlay Recommendations Consideration could be made to milling and overlaying the existing pavement. The roadway sections appear to have a sufficiently thick in place pavement section, over a majority of the project alignment, which would lend itself to rehabilitation via mill and overlay techniques. In general, pavement sections consisting of 3 inches or less of bituminous asphalt can be difficult to effectively mill and overlay as often times the entire pavement section is reclaimed during the attempted partial section milling process. Additionally, in locations where the existing pavement thickness is less than the recommended thickness, a mill and overlay would not be recommended unless a structural overlay were applied to increase the overall thickness. Pavement Reconstruction If the pavement section is to be removed and replaced in its entirety, the most conservative method of subgrade preparation would be 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 relatively a- typical method of subgrade preparation for improvements to existing municipal roadways. If the City is willing to accept some risk in potential long term detrimental performance for the significant upfront savings, the roadway can be reconstructed over the existing fill. NTI recommends that prior to installing the aggregate base, the existing subgrade should 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. 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 rutting or localized unstable subgrade areas are observed, those areas should be subcut, moisture - conditioned, and re -compacted or removed to a stable depth. Page 5 of 7