07-27-1994 Council Agenda - Laserfiche WebLink

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Page Four such as compaction test results, which would have been performed at the time the fill was placed and therefore there is no absolute assurance that the fill is uniform in composition and density. We must caution you that relying on the existing fill for support of your new structure will include some minor risk. This risk would be one of excessive differential settlement due to variations in the composition and density of the fill or potential for compressible soils being present below the fill, factors which would not be detected at the time of construction. Grading Recommendation - For preparation of the building, we recommend stripping of surficial vegetation and disturbed soils to expose the top of the fly ash fill system. We then recommended removal of peat soils (northeast quadrant) using a backhoe. This would involve a subcut of about 8' at boring 3, about 5' at test pit 2 and 5.3' at test pit 1. Ideally, the deeper subcut through the peat should be followed by placement of a controlled granular fill, using sand soils having less than 15% passing the #200 sieve. The material should be compacted in thin lifts to at least 95% of the Standard Proctor value. The excavation should be observed by a geotechnical engineer prior to fill placement. The test pit work documented several areas where the upper portion of the fly ash fill was loose. We recommend that these areas be reworked or the fly ash be removed and replaced. Thus, the excavation into the fly ash fill system should terminate upon firm fly ash material only, at final subcut grade. The remainder of the building area should then be brought up to grade, preferably by use of a granular compacted fill. Again, the fill should be placed in thin lifts and compacted to 95% of the Standard Proctor value. Where perimeter footings are to be supported on new fill, the excavation bottoms should be laterally oversized a minimum distance of 1' for each foot of fill required below footing elevation; i.e., a 1:1 lateral oversize. This is required for proper support of the lateral loads exerted by the footings through the fill system. Foundation Recommendations - It is our judgement that spread footing construction bearing on the fill can then be utilized. All exterior footings in heated areas should be placed at a minimum depth of 42" below final exterior grade for frost protection. Interior footings in these areas can be placed at a convenient depth below the floor slab, bearing on suitable material. Any footings (both - interior and exterior) required in unheated areas should be extended to a minimum depth of 60" below final exterior grade. Where possible, we recommend the footings be placed as high as possible, in order to provide for compacted sand fill below the footings, particularly for the interior column pads where we anticipate the loads will be greatest. Page 54