09-27-1989 Council Agenda - Laserfiche WebLink

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F M Frattalone Excavating 8 Grading April 7, 1987 Page Three addition, if unusually soft clays are encountered below the topsoil, the subcut should be extended. The subcutting should be performed in such a manner as to not disturb the underlying sensitive soils. The select granular compacted fill used should be compacted to 100% of the Standard Proctor value within the upper 31 of the subgrade zone. In the event fill is placed beneath the 3' level, a reduced level of 95% can be used for these fill soils. As previously indicated, the southern portion of the site, in the area of boring 2, has existing grades at or perhaps slightly above final street grade. Therefore, a minimum excavation in this area would result in removal of surficial vegetation and portions of the silty sand topsoil below. As a minimum, we suggest that any highly organic silty sand layers be removed along with the surficial vegetation. Our experience in this area together with the examination of the boring samples indicated that the silty sand topsoil is not highly organic. If properly scarified and recompacted at about its optimum moisture content, it is our judgment that this material could be reused in -place as the granular subgrade material. Under these conditions, it is our opinion that R- values on the order of 30 -40 can be assumed for the reworked silty sand subgrade material. You indicated that in the southern portion of the First Addition, just east of a portion of the Second Addition, you had utilized the natural silty sand layer in -place and did not experience problems with this subgrade layer. Based on our observations, we confirm that the pavement is performing satisfactorily in this southern part of the First Addition. If portions of this silty sand strata become disturbed or found to be unusually wet or loose or if clay soils are included within the profile, localized subcutting and refilling may be needed to correct the condition. This proposed street will be subject to quite heavy axle loadings during construction, due primarily to concrete ready -mix trucks, fill haul trucks and so forth. For best future performance of the, street profile, we would strongly suggest that actual paving be delayed until the following season, at which time construction should be essentially completed. In addition, this will permit periodic corrections of the surficial weak zones which may develop during construction to occur without removal and replacement of bituminous pavement. Consthuction Observations & Testing We recommend a geotechnical engineer be retained on an as needed basis to observe questionable subgrade conditions that may arise during earthwork procedures. Also, we recommend compaction tests be performed in all fill soils placed to document that the soil system has achieved adequate compaction at the appropriate moisture content levels. Page 86