7200 HARDESON RD 2016-01-01 MF Import

�� C N ��M �� s �� �'+ � a• t" y N � M �� �� � �� � ' � CNA Architecture Group 12 April 1991 r • W-7352 Page 7 If, during stripping, areas of soft, wet, or pumping subgrade or deeper organic rich soils are encountered, these areas should be over-excavated and backfilled with "structural fill" as recommended below. Areas excavated to native bearing, design subgrade elevations, or areas to receive structural fili should be prerolied with a vibratory roiler to a firm, nonyielding condition if they are near their optimum mois!ure level. We recommend that prerolling be accomplished such that the upper 12 inches of the exposed native or non-organic fill soiis is compacted to a density of at least 95 percent of the laboratory maximum, using the modified Proctor method (ASTM:D-1557) as the density standard. If the subgrade is more than 2 percent above the optimum moisture content, adequate compaction of the site soiis may be difficuit or impossible to achieve. Prerolling of the silry subgrade soiis may actually initiate site disturbance in wet weather conditions. Under such conditions, it may be necessary to scarity ihe upper layer of wet subgrade soils, allow them to dry and then recompact. If this is not practical, it may be necessary to remove the wet soils. Depending on the final grades and site conditions during construction at the discretion of the geotechnical engineer, it may be acceptable to strip the ground surface as much as possible and p!ace fill directly on the native ground surface without prerciling. If �rading must be initiated when areas of silty site soils are more than about 2 percent wetter than optimum, those areas to receive fill should be blanketed with a clean, coarse gravel, crushed rock, quarry spalls or equivalent non- moisture sensitive material as described above to provide a working surface for the subsequent structural fiil placement. The contractor should be aware of the fact that the silty site soils are highly susceptible `j to disturbance when they are only slightly wetter than optimum. Therefore, the e� contractor would need to perform the final stripping with care in order to minimize site � disturbance. Additionally, the contractor should avoid vehicuiar traffic above prepared � subgrade areas, especially in wet weather or wet site conditions. 5.2 Structural Fill All fill placed beneath building areas and walkways, as well as utility trench ba,rcfill, should be piaced in accordance with the foilowing recommendations for "structural tili". Prior to placement of structural fill, the surfaces to receive fill sho��ld be prepared as previously recommended by excavation to native soils, foilowed by prerolling and