Forensic Evaluation of Engineered Fills 1

[Ihatelawyers]

Reading ASTM E141 it seems to me that when evaluating existing fills the standard practices of our industry are falling short. E141 indicates that location of and evaluation of the units being examined (dry density of the engineered fill) should be performed in exactly the same way as done for the sample (i.e. nuc's or sand cones during construction). That is ... using SPT unit weights (or shelby, or whatever) to evaluate the relative compaction of an engineered fill is bunk. Am I reading E141 right? Seems like the degree of precision and accuracy needed for unit weight determination for geotechnical analysis would fall short of the accuracy and precision bar necessary for verification of an engineered fill.

 

[oldestguy]

Learning the hard way with 95 percent.

A new college campus on an area of high-shrink swell clay had several buildings built on a few feet of compacted clay fill, dug from proposed ponds. The conscientious engineer demanded and got 95 percent. Subsequent feeding of roof drain water, fed via sand filled plumbing trenches, caused major heaving of floors, damaged interior partitions, etc.(fortunately footings were much lower in natural ground). We were darned lucky the insurance coverage was there or we would be broke.

In clay ground, I have been very careful not to do that again. (It was not me, but a nameless fellow engineer ).

 

[BigH]

In the ASCE Special Publication #68, "Unsaturated Soil Engineering Practice", there is a paper by Noorany titled "Structural Fills: Design Construction and Performance Review" that might be of interest. In it, " . . . strict adherence ot this code requirement (added note - 90% MDD ASTM D1557 in UBC)is contrary to good and rational engineering, and impliesthat regardless of expansion potential it is desirable to compact all soils to 90 percent relative compaction. Indeed, such heavy compaction can be harmful and can cause high expansion of most soils used in structural fills in California. See the article for other good information.