Agenda - Council - 01/13/2015 - Laserfiche WebLink

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It is especially important that trench backfill for utility construction within paved areas be thoroughly compacted to minimize future pavement damage. We recommend that such soils be compacted to those included in general compaction criteria guidelines described in Appendix B. The stability of embankments along utility excavations is dependent on soil strength, site geometry, moisture content, and any surcharge load for excavated soils and equipment. We present cautionary remarks concerning stability of excavation side slopes in the “Excavation Stability” section of this report. The Contractor is solely responsible for assessing the stability of and executing underground utility and project excavations using safe methods. The contractor is also responsible for naming the “competent individual” as per Subpart P of 29 CFR 1926.6 (Federal Register - OSHA). Site Preparation The Contractor must realize that the silty and clayey subgrade soils will be moisture-sensitive, and protecting them from inclement weather will aid in maintaining stability. 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. Pavement Recommendations Due to the relatively thin section of existing bituminous pavement, milling and overlaying is not a practical option. Reclaiming the existing bituminous pavement and aggregate base or completely reconstructing the streets would be more practical alternatives to repair the streets. For either alternative that is selected, prior to installing the aggregate base, the prepared subgrade should be scarified and re-compacted to a depth of at least 12 inches. After scarification is complete, a proofroll test should be performed to determine soft or unstable subgrade areas. If rutting or localized unstable subgrade areas are observed, those areas should be subcut, moisture-conditioned, and re-compacted or removed to a stable depth. Subgrade corrections should be anticipated based on slightly organic, soft and wet conditions that were observed in borings SB-1 and SB-2. Areas with conditions similar to these borings are less likely to pass proof roll tests, therefore we recommend provisions be provided for additional excavations. Excavations for soil corrections in paved areas should allow for a 2 foot oversize beyond the edges of the pavement. If imported fill is required in paved areas it should consist of debris free granular soils, and should have 100 percent passing the 1 ½ inch sieve, and less than 20 percent passing the U.S. Number 200 Sieve. Individual lifts of engineered fill should be tempered for moisture content, placed and compacted as listed the guidelines and table in Appendix B. 4