Res. #15-036 - Approving Plans & Specs. & Ordering Ad. For Bids

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City of Centerville Project SP-07-03738 November 29,2007 Page 8 Organic soils may also adversely affect the performance of new utilities if present and left in place near the bottom or surrounding the utilities. For this reason,organic soils are not considered suitable for utility support or use as utility backfill. We recommend subexcavating them from below utilities and replacing it with suitable compacted backfill. CA. Reusing On-Site Materials On-site materials free of organic debris consisting of poorly graded sand,silty sand,clayey sand and sandy lean clay are considered suitable for reuse as structural backfill. As indicated by the results of the moisture content tests,the clay-and silt-rich soils encountered do not appear to be over their optimum moisture content These soils,however,will become difficult to compact if they become wet. In this case,we recommend that those materials be sufficiently dried prior to reuse as structural backfill. Organic soils,in our opinion,should be placed in landscaped areas, if not hauled from the site to a disposal area. In our opinion,depending on how the bituminous and aggregate base are removed/reclaimed,it is possible that they can be mixed and reused as general subgrade fill below subgrade elevations or to help stabilize unstable subgrade soils. C.S. Groundwater Considerations During drilling,we observed groundwater in the boreholes of Borings ST-3,ST-9 and ST-12 at depths ranging from 6 to 8 feet. This being the case,it appears that excavations will likely encounter groundwater and wet materials. Provisions should therefore be made to pump water out of excavations and stabilize wet excavation bottoms,if necessary to facilitate construction. CA Consideration for Unfavorable Weather In general,the months of June,July and August are most favored for grading operations,particularly if there are silt-or clay-rich soils that require drying. Cooler temperatures and wet weather conditions earlier in the spring,in the fall and through the winter tend to slow or delay grading and construction. Silt-and clay-rich soils that become saturated during cool or wet periods will be difficult to dry and will provide limited support to heavy construction equipment;rubber-tire vehicles and even heavy tracked dozers can disturb otherwise competent soils,increasing the effort required to stabilize or correct and pavement subgrades.