I am working on a site where we are adding several feet of fill material. The underlying soils are saturated clayey sand soils (SC). The fill material is a slightly silty sand (-200=12 to 15%) with a modified proctor of 119 pcf and 11% moisture. We have two feet of fill in above the wet clayey soils (SC). The fill material was tested to be at 96 to 98% compaction of the modified proctor maximum dry density with an in-situ moisture of about 10%. However, poritons of the building pad were yielding and pumping under the weight of a human (i.e. me walking on the site). The fill was placed and compacted with a vibratory roller. I believe the vibratory roller caused the underlying satrurated clayey sand soils (SC) to lose shear strength. I believe the underlying clayeys soils will stabilize once the excess pore water pressures built up from the vibratory roller have had a chance to dissipate. The contractor has obviously passed the fill compaction requirement of 95% MPMDD, but the pumping subgradein the buidling pad is not acceptable. What to I need to do or what should I tell the contractor? Should they continue to place fill to see if they can bridge the underlying soft soils? Thanks for your help!
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