Pumping subgrade, but passing compaction tests? Help!
Pumping subgrade, but passing compaction tests? Help!
(OP)
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!





RE: Pumping subgrade, but passing compaction tests? Help!
Yes, the soil will stabilize when the pore pressures dissipate; however, load should not be placed on the soil until that happens. If you place fill on top of the existing, make sure it is dry of optimum, which will tend to pull moisture from the underlying soils and help dissipate the excess pore pressure.
Use static compaction only at this point.
RE: Pumping subgrade, but passing compaction tests? Help!
Your situation just highlights the issue of just specifying compaction density and moisture content ranges. Add in the requirement that fill must be stable, and define what you'll accept with respect to defining stable fill.
Finally, if you accept the fill construction, you'll also accept future problems with improvements - the contractor will certainly remember you accepted the construction of the fill as is. Proceed carefully!
RE: Pumping subgrade, but passing compaction tests? Help!
RE: Pumping subgrade, but passing compaction tests? Help!
RE: Pumping subgrade, but passing compaction tests? Help!
RE: Pumping subgrade, but passing compaction tests? Help!