Agenda - Council - 02/10/2015 - Laserfiche WebLink

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NTI further recommends that compaction of the supporting soils be completed and tested to ensure it meets 95 percent standard Proctor dry density, which would require observation and testing to be performed both prior to and during backfilling operations. Lastly, NTI recommends that all import fill be approved by NTI or the City's representative. NTI also provides new bituminous pavement construction recommendations in their report. NTI concurs the existing pavement is too thin and deteriorated to mill or overlay and that it would be more practical to reconstruct these streets. NTI recommends reconstructing the pavement section using 6" of class 5 aggregate base, 2" of bituminous base course, and 11/2" of bituminous wear course. NTI also recommends that stripping of the existing pavement and aggregate base course should occur immediately prior to subgrade preparation and base aggregate installation to minimize weather -induced instability due to prolonged exposure to the elements. NTI recommends correcting the subgrade soils by scarifying and re -compacting a minimum of 12" of subgrade soils, then proof rolling the soils using a tandem axle dump truck loaded to gross capacity (20 tons minimum) prior to placing aggregate base class 5 and bituminous pavement. NTI also recommends that if any rutting or localized unstable subgrade areas are observed during proof rolling, those areas should be subcut, moisture -conditioned, and re -compacted or removed to a stable depth. NTI also noted that subgrade corrections should be anticipated based on the slightly organic, soft and wet conditions observed in borings SB -1 and SB -2, both of which were taken along Garnet Street. NTI also states that areas with conditions similar to these borings are less likely to pass proof roll tests, and therefore recommend that provisions be provided for additional excavations, and that excavations for soil corrections in paved areas should extend 2 feet beyond the edges of the pavement. NTI estimates that a properly prepared subgrade for Garnet Street and 168th Avenue will have an average stabilometer R -value of 30. NTI's pavement recommendations assume the subgrade soils and aggregate sections below paved surfaces drain to subsurface piping for eventual discharge into storm sewer. In addition, due to the relatively thick layer of soft and potentially compressible clay soil observed in the borings, long term secondary settlement may continue to occur near soil boring SB -2 and other areas with similar subsurface conditions. NTI's report also presumes that soil correction excavations to remove soft fat clay layers (CH) are likely not a practical option so additional maintenance may be required to fill cracks or build up settled areas. As such, NTI states the City should anticipate some minor road maintenance and repairs will be required in these areas in the future. Feasibility Report Garnet Street and 1681" Avenue Reconstruction City of Ramsey Project No. 13-10 Page 6