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December 20, 1999 Burgess Res. Page 3 FOUNDATION RECOMMENDATIONS The site resides in a known area of surface organic soils which are both expansive and compressible, even under relatively light loads associated with wood frame structures. This is evident by the settlement and expansion damage which has been seen by our office in the local area during foundation investigations for additions to some of the older home additions. Damage includes minor to moderate floor slab cracking and heaving and sloped raised wood floors due to settlement at the house corners. The strata most susceptible to consolidation and expansion is the upper 2 feet of organic silt. For this reason foundations should be carried through the surface organic silt. In addition, the subgrade for the new garage slab should be pre-saturated to minimize the expansive affect of the surface soil. Initially the proposed garage pad or any other slab-on-grade structure should be cleared of any existing vegetation and/or debris. Any buried structures or root debris encountered should be removed. Voids resulting from their removal should be cleaned out of all loose soil and debris so that they may be backfilled with engineered fill during filling operations. After the pads have been cleared the subgrade thus exposed should be scarified, moisture conditioned, and recompacted as indicated in Appendix A with the following modification: All scarified and recompacted subgrade and on-site organic soil below the top 18 inches of finished pad grade shall be placed and compacted to a minimum 90 percent relative compaction,at a minimum of 3 percent above optimum moisture content as determined in ASTM 1557. All on site clay soil that is utilized for fill in the top 18 inches of the building pad shall be compacted between 85 and 90 percent relative compaction, at a minimum of 5 percent above optimum moisture content. If compaction in the upper 18 inches is in excess of 90 percent or the required minimum moisture content has not been achieved, the fill or recompacted subgrade will be considered unacceptable and reworking of the fill or subgrade shall be required. It is important that the upper 18 inches of the building pad not be over-compacted as this will greatly lengthen the pre-saturation time needed and possibly cause the soil to heave or rebound. Fill placed for the slab subgrade should be placed as engineered fill as recommended in Appendix A with the noted modifications. The engineered fill should extend at least 5 feet beyond the perimeter of any foundations. On site soils soils are suitable for use as engineered fill if the above conditions are met. Foundations for the residence should consist of continuous spread/stem wall footings. Isolated interior piers should not be used. Footings should be a minimum of 12 inches wide and bear 48 inches below grade. Footing excavations may be backfilled with a lean grout mix(2 sack)up to within 24 inches of the subgrade. Spread/stem wall footings may then be cast directly on the lean Sooti � M r Q � 1 o GS G♦ r