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Everett General Hospital & Medical Center W-5557 <br /> 29 Marcr. 1988 Page 4 <br /> actual depth of the top of very dense soil may be slightly higher than indicated, <br /> if the change actually occurred between sampling attempts. Rittenhouse-Zeman & <br /> Associates assumes no liability for errors or omissions in the previous studies <br /> accomplished by others on which we have relied. <br /> 4.0 CONCLUSIONS AND RECOMMENDATIONS <br /> The following geotechnical recommendations are based on the project description <br /> as summarized previously, and the subsurface soil and ground water conditions <br /> encountered in borings completed for this project. In the event that subsurface <br /> conditions encountered by foundation excavations vary between the boring locations <br /> from those encountered by the borings, Rittenhouse-Zeman & Associates, Inc. (RZA) <br /> should be contacted to provide modification or confirmation of geotechnical <br /> recommendations contained in this report. <br /> 4.1 Site Preparation <br /> Site preparation shoi•ld include removal of existing pavement, curb elements and <br /> existing utilities. Following excavation to design subgrade level, the ground <br /> surface to support floor slabs should be prerolled with a self-propelled, vibratory <br /> soil compaction roller. We recommend that RZA observe the prerolling, to recommend <br /> additional excavation if appropriate. The prerolled surface should be firm and <br /> non-yielding under the passage of the roller, and should be compacted to at least <br /> 90 percent of modifiei Proctor maximum dry density (ASTM:D 1557). If existing <br /> fill soils, disturbed or loose soils, or organic-rich materials are encountered, <br /> they should be removed and the excavation backfilled in accordance with <br /> recommendations presented subsequently in this report. <br /> The subgrade soils in the building area should be protected by the contractor from <br /> disturbance during wet site conditions. Towards this end, we recommend that site <br /> work be scheduled only during extended dry weather periods. It may be prudent to <br /> spread a working surface of clean, well-graded sand and gravel over the exposed <br /> 1 floor slab subgrade following excavation. The sand and gravel should meet the <br /> recommendations for wet weather structural fill contained in this report. Footing <br /> excavations should all extend to firm, non-yielding very dense soil as described <br /> J <br />