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Alpine Drive—Street Improvements <br /> Ramsey,Minnesota <br /> NTI Project No.16.61770.100 <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 /> If imported fill is required in paved areas it should consist of debris free, non-organic, mineral soil similar <br /> in composition to the subgrade soils encountered in the surrounding areas. If sand is imported into <br /> areas that are underlain by relatively impervious fine grained soils the sand layer must be drained with <br /> drain tile in order to prevent frost heave from water trapped within the imported sand layer during <br /> freezing temperatures. Individual lifts of engineered fill should be tempered for moisture content, <br /> placed and compacted as noted in the "Placement and Compaction of Engineered Fill" section in <br /> Appendix B of this report. <br /> The performance of stabilometer or similar tests, were beyond the scope of this report; however,they <br /> may be performed, upon request,for an additional fee. Based on the encountered soil conditions, we <br /> estimate that a properly prepared poorly graded sand with silt (SP-SM) and poorly graded sand clay(SP- <br /> SC) soils will have an average stabilometer R-Value of 40. <br /> For a 20-year design pavement life,Table 3 presents our thickness recommendations for flexible <br /> (bituminous) pavement. These recommendations were based upon the encountered subgrade <br /> conditions, estimated R-value for the existing subgrade soils, the assumed AADT volumes, and the City <br /> of Ramsey's typical pavement section for the respective project area. <br /> Table 3: Flexible Pavement Thickness Design' <br /> Alpine Drive <br /> Calculated Required City's Typical <br /> Pavement Section Pavement Section Pavement Section <br /> Bituminous Wear Course(inches) 1.5 1.5 <br /> Bituminous Base Course(inches) 2.0 2.0 <br /> Class 5 or 7 Aggregate Base(inches) 6.0 4.0 <br /> 1. Assumed AADT volume of 1000 and an average R-value of 40. <br /> 2. The calculated required section was greater than the City's typical section for residential streets,thus NTI <br /> recommends that the Calculated Required Pavement Section be implemented. <br /> Page 6 of 8 <br />