Agenda - Council - 01/13/2015 - 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 requireobservationand testing to be performed both prior to and during backfilling operations.Lastly, NTI recommends that all import fill be approved by NTIor the City’s representative. NTIalso providesnew bituminous pavement constructionrecommendations 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 1½” of bituminous wear course.NTI also recommendsthat stripping of theexisting pavement and aggregate base course should occur immediately prior to subgradepreparation and base aggregate installation to minimize weather-induced instabilitydue 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 soilsusing a tandem axle dump truck loaded to gross capacity (20 tonsminimum)prior to placing aggregate base class 5 and bituminous pavement. NTI also recommends that ifany rutting or localized unstable subgrade areas are observedduring proof rolling, those areas shouldbe subcut, moisture-conditioned, and re-compacted or removed to a stable depth. NTI also noted that subgradecorrections 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 lesslikely to pass proof roll tests, and therefore recommend that provisions be provided for additionalexcavations, and that excavations for soil corrections in paved areas should extend 2feet beyond the edges of the pavement.NTIestimatesthat a properly prepared subgrade for Garnet Street and 168th Avenuewill have an average stabilometer R-value of 30. NTI’s pavement recommendations assume thesubgrade soils and aggregate sectionsbelow pavedsurfaces drain to subsurface piping for eventual discharge into storm sewer.In addition, due to the relatively thick layer of soft and potentially compressible clay soilobserved in the borings, long termsecondary settlement may continue to occur near soil boring SB-2 and other areas with similarsubsurface conditions. NTI’s report also presumes that soil correction excavationsto remove soft fat clay layers(CH) are likely not a practical optionso additional maintenance may be required to fillcracks or build up settledareas. As such, NTI states the City shouldanticipatesomeminor road maintenance and repairs will be required in theseareas in the future. Feasibility Report th Garnet Street and 168Avenue Reconstruction City of RamseyProject No. 13-10 Page 6