Agenda - Council - 01/12/2021 - Laserfiche WebLink

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Ramsey Tiger Street Infrastructure Replacement Project #: 17623.20. M NS D.2. Trench Sidewalls December 11, 2020 Page - 5 The contractor will be required to slope or shore the excavations as needed to meet OSHA requirements for safety. Most of the soils would be expected to classify as Type C soils as defined by OSHA. Trench boxes or other stabilization methods may be necessary if excavations encroach near existing utilities or structures. D.3. Trench Bottom Stability Depending upon location and depth, the utilities are expected to bear primarily on clean sands. These materials are considered generally suitable for support of pipes. If soft and unstable conditions are encountered, we recommend placing bedding of coarse sand or gravel at the base of the trenches to provide a more stable bottom for crews laying the pipes. In order to reduce the potential for point loads on the pipes, we recommend removing any cobbles or boulders to a depth of at least 6 to 8 inches from around pipes and replacing those materials with clean sand or gravel that can more readily conform to the pipes. DA. Fill Placement and Compaction Soils placed as backfill below paved areas should ideally be compacted to 100% of their maximum standard Proctor density (ASTM D 698) in the upper 3 feet, and to at least 95% below. In green areas, 90% compaction is normally adequate. The onsite soils are considered generally suitable for use as backfill above utilities, provided they can be adequately compacted. To reduce potential for differential frost action, fill placed in upper part of the trenches should ideally be placed in layers that align reasonably similar to the soil stratification on the trench side walls. In this case, all the soils appear to be reasonably uniform and layering does not appear to be necessary. E. Pavement Recommendations E.I. Stripping and Grading We recommend removing the existing asphalt, aggregate base, and any organics soils from within 3 feet of the proposed pavement section subgrade before placing any new pavement material sections. It may be possible to reclaim and reuse the existing asphalt and aggregate for use as part of the new pavement's aggregate base, provided it meets MnDOT specifications. That being said, the existing paving materials appeared to be quite varied — with little or no apparent aggregate base in most areas and asphalt materials that were thin or layered with recycled materials. After the removals, utility construction, and grading, the near -surface soils are expected to primarily consists of clean sands and silty sands. We recommend scarifying and compacting all near -surface soils in order to even out any localized discontinuities in the subgrade materials and to provide a more gradational transition between differing materials. This action is intended to limit differential frost heave and provide more uniform pavement support. M I N N E S 0 T A 1 0 W A W I S C 0 N S I N