Agenda - Council - 02/14/2017 - Laserfiche WebLink

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Alpine Drive — Street Improvements Ramsey, Minnesota NTI Project No. 16.61770.100 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. 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 must be drained with drain tile in order to prevent frost heave from water trapped within the imported sand layer during freezing temperatures. 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. The performance of stabilometer or similar tests, were beyond the scope of this report; however, they may be performed, upon request, for an additional fee. Based on the encountered soil conditions, we estimate that a properly prepared poorly graded sand with silt (SP-SM) and poorly graded sand clay (SP- SC) soils will have an average stabilometer R-Value of 40. For a 20-year design pavement life, Table 3 presents our thickness recommendations for flexible (bituminous) pavement. These recommendations were based upon the encountered subgrade conditions, estimated R-value for the existing subgrade soils, the assumed AADT volumes, and the City of Ramsey's typical pavement section for the respective project area. Pavement Section Table 3: Flexible Pavement Thickness Design' Alpine Drive Calculated Required City's Typical Pavement Section Pavement Section2 Bituminous Wear Course (inches) Bituminous Base Course (inches) Class 5 or 7 Aggregate Base (inches) 1.5 2.0 6.0 1.5 2.0 4.0 1. Assumed AADT volume of 1000 and an average R-value of 40. 2. The calculated required section was greater than the City's typical section for residential streets, thus NTI recommends that the Calculated Required Pavement Section be implemented. Page 6 of 8