2009-04-29_PERMIT FILE - C1982056 (6)

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2) The piers should be designed using an allowable skin friction value of 4,000 psf for the portion of • the pier drilled into the claystone bedrock. The upper 5 feet of the pier penetration should be neglected in the skin-friction calculations. If a drill rig of sufficient size, type and operating condition is used, and the bottom of the piers can be cleaned out properly and approved by this office, then an allowable end bearing pressure of 40,000 psf can be used for the piers drilled into the undisturbed claystone bedrock. 3) The piers should be reinforced their full length with at least one #5 reinforcing rod for each 16 inches of pier perimeter. 4) The piers should be properly cleaned and dewatered prior to steel and concrete placement. 5) A 4-inch void should be provided beneath grade beams to prevent the swelling soils from exerting uplift forces on the grade beams and to concentrate pier loadings. A void should also be provided beneath necessary pier caps. 6) A representative of this office should observe the pier drilling operations. Alternate Foundation Recommendations An alternative deep foundation system to drilled piers would be to advance helical/screw piles into the underlying claystone bedrock. The helical/screw pile foundation system should be designed by a qualified engineer, using industry standards and be installed by a licensed/certified installer. We strongly recommend that at least three test piles be advanced across the site so that the torque versus depth relationships can be established and the proper shaft and helix size and type can be determined. A representative of this office should observe the helical/screw pile installations. Floor Slab Recommendations It is our understanding that slab-on-grade construction is not anticipated at this time. However, if slab-on- grade floor systems are used at the site, we recommend that the design and construction precautions provided below be followed. The on-site soils and bedrock materials, with the exception any topsoil and organic materials, are capable of supporting slab-on-grade construction. However, floor slabs present a very difficult problem where expansive soils and bedrock materials are present near floor slab elevation because sufficient dead load cannot be imposed on them to resist the uplift pressure generated when the materials are wetted and expand or when the soils consolidate under relatively light loads. Based on the moisture-volume change characteristics of the natural clays and claystone bedrock materials encountered at • this site, we believe slab-on-grade construction may be used, provided the risk of distress resulting from slab movement is recognized and special design precautions are followed. Job Number: 08-8241 NWCC, Inc. Page 5