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Sunwood Drive—Street Improvements <br /> Ramsey,Minnesota <br /> NTI Project No.16.61770.100 <br /> Engineered Fill and Winter Construction <br /> The silty sand soils on this site will be susceptible to frost action if not provided adequate drainage, <br /> insulation or coverage. Frozen soil should not be used as backfill. When the ambient air temperature <br /> falls below freezing for an extended period of time, frost forms, and soil near the surface grade expands. <br /> Settlement of the fill may occur as the frozen soils thaw. <br /> If frost penetrates the soil prior to paving, soils must be thawed, scarified, and re-compacted as <br /> recommended in this report. Subgrade soils should be inspected prior to paving to verify frozen <br /> conditions are not present. <br /> PAVEMENT RECOMMENDATIONS <br /> Mill and Overlay Recommendations <br /> Consideration could be made to milling and overlaying the existing pavement. The roadway sections <br /> appear to have a sufficiently thick in place pavement section, over a majority of the project alignment, <br /> which would lend itself to rehabilitation via mill and overlay techniques. <br /> In general, pavement sections consisting of 3 inches or less of bituminous asphalt can be difficult to <br /> effectively mill and overlay as often times the entire pavement section is reclaimed during the <br /> attempted partial section milling process. Additionally, in locations where the existing pavement <br /> thickness is less than the recommended thickness, a mill and overlay would not be recommended unless <br /> a structural overlay were applied to increase the overall thickness. <br /> Pavement Reconstruction <br /> If the pavement section is to be removed and replaced in its entirety,the most conservative method of <br /> subgrade preparation would be remove the undocumented fill soils and replace them in their entirety <br /> with properly compacted engineered fill. This method of subgrade preparation would provide the most <br /> uniform subgrade but would also be the most costly method of construction and would be relatively a- <br /> typical method of subgrade preparation for improvements to existing municipal roadways. <br /> If the City is willing to accept some risk in potential long term detrimental performance for the <br /> significant upfront savings, the roadway can be reconstructed over the existing fill. NTI recommends <br /> that prior to installing the aggregate base,the existing subgrade should be scarified and re-compacted <br /> to a depth of at least 12 inches. A proof roll test should then be performed to determine soft or <br /> unstable subgrade areas. The proof roll should be performed with a tandem axle dump truck loaded to <br /> gross capacity(at least 20 tons). Acceptance criteria of the proof roll shall be limited to rut formation no <br /> more than one inch depth (front or rear axles) and no pumping (rolling) observed during the visual <br /> inspection. Proof roll tests should be observed by an experienced technician or geotechnical engineer <br /> prior to placement of the aggregate base course to verify the subgrade will provide adequate pavement <br /> support. <br /> If rutting or localized unstable subgrade areas are observed,those areas should be subcut, moisture- <br /> conditioned, and re-compacted or removed to a stable depth. <br /> Page 5 of 7 <br />