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City of Centerville <br /> Project SP-07-03738 <br /> November 29,2007 <br /> Page 12 <br /> D.5. Utilities <br /> D.5.9. Excavations <br /> Note that soils encountered by the borings are Type C materials under Department of Labor and <br /> Occupational Safety and Health Administration(OSHA)guidelines. Excavation sideslopes in these <br /> materials should therefore be maintained at gradients equal to or flatter than 1 3/2:1 (horizontal:vertical), <br /> or be shored. <br /> D.5.b. Subgrade Stabilization <br /> Where unstable soils prohibit the excavation backfill from being adequately compacted,we recommend <br /> that they be subexcavated and replaced with no less than l foot of clean crushed aggregate having a <br /> maximum size of I inch. Subexcavation depths may be greater depending on soil conditions and the <br /> magnitude of the structure. <br /> D.5.c. Selection,Placement and Compaction of Backfill <br /> Backfill for utilities should be selected,placed and compacted according to Section D.1. <br /> D.5.d. Dewatering <br /> Where excavations encounter groundwater,with the types of soils that exist on this site,it is anticipated <br /> that a system consisting of sumps and pumps will be capable of controlling groundwater seepage to keep <br /> excavations"dry"and facilitate construction. <br /> D.6. Construction Observations and Testing <br /> D.6.a. Observations <br /> We recommend having a geotechnical engineer observe all excavations related to subgrade preparations <br /> and pavement construction. The purpose of the observations is to evaluate the competence of the <br /> materials exposed in the excavations,and the adequacy of required excavation oversizing. <br /> D.6.b. Materials Testing <br /> We recommend density tests be taken in all backfill and fill placed below pavements. We recommend <br /> density tests to evaluate compaction. We also recommend slump,air content and strength tests of <br /> Portland cement concrete_ <br /> D.6.c. Cold Weather Precautions <br /> If site grading and construction is anticipated during cold weather,all snow and ice should be removed <br /> from cut and fill areas prior to additional grading. No fill should be placed on frozen subgrades. No <br /> frozen soils should be used as fill. <br /> 47 <br />