Artificial Fill

[ohengineer]

In ASCE Manuals and Reports on Engineering Practice - No. 56 "Subsurface Investigation for Design and Construction of Foundations of Buildings," there is a section on Artificial Fill that states that "Unless the conditions and control under which it was placed are fully known, fill should be presumed unsatifactory." This book was published in 1976 and I was wondering if anyone is aware of a more recent publication that states something similar. Thanks

 

[msucog]

IBC pretty much says that in chapter 17 and 18.

 

[kevgeotech]

Why would you want to assume fill placed under unknown conditions is anything but unsatisfactory. It is simple enought to perform a series of borings (hand auger or with a drill rig), obtain Shelby tube samples from various depth(s), run a Proctor on the cuttings of the borings and calcuated the in-place density of the suspected fill. I would estimate we do two or three such jobs a month for contractors who wanted to save on testing fees during the construction and now need an engineered letter to obtain their CO.



Kevin P. Morrow, P.E.
Senior Geotechnical Engineer
D Miller & Associates, PA

 

[theCorkster]

Borings and test pits in existing fill provide a glimpse of what might be in fill, and that is all. However, what is interesting is that that by doing this and providing an opinion regarding the suitability of the fill to perform, we are actually exposing ourselves to greater liability than doing so in natural formations (as it should; who really knows what occurred during fill construction).

I've seen numerous sites where "reputable" real estate brokers, contractors and even owners have adamantley defended the quality of fill and workmanship performed years before on property, and then during final site development find unsuitable fill material, debris, bury pits, and even old automobiles. When that happened the owner, contractor and other parties tended to look toward their geotechnical engineer that presented such an opinion, primarily to contribute to relief of the problem.

Since the propety seller/buyer and/or developer is in essence making money by not spending money to construct such fill to engineered standards (observation, tests, and documetation) and you by accepting this assignment are transfering risk to you (through your opinion), make sure you have a clear written agreement that will stand up in court as to who will be responsible for addressing delays and additional engineering and/or construction on the project.

 

[msucog]

i never trust old fill and am always suspicious since i've seen too many instances of what could exist...seen it from both contractor and engineer. as a contractor, it's absolutely mind-blowing amazing what happens as soon as the testing firm or owner isn't looking. as an engineer, even with borings, test pits, etc. you should always remain cautious and let the owner make the final decision even if the stuff looks "okay" (for lightly loads structures that is). in other words, if you can't find some obviously gleaming reason why the old fill should come out after performing an extensive exploration program, the owner must acknowledge and accept the risks associated with leaving it in place.

by the way, i've seen many big projects be graded and sit for years. as part of that development, the not-so-good stuff (topsoil, strippings,etc) get wasted in "non-structural landscape" areas. then 10 years later, no one seems to remember that and you end up with a building on the area. and sometimes, even when you absolutely know the stuff is there, you have a very hard time hitting it was borings or even test pits.

ibc requires observation of new fill placement along with testing at regular intervals. so i suspect that it will soon actually be enforced more widespread as part of the permit...it already is in some/many areas. it also requires a soil report of subsurface conditions.

 

[BigH]

I think that one point to be made is with regards to "poor sites". Yes, test pits and borings are only "good" at the locations of the investigation. Still, it can give a good handle - i.e., sand fill? miscellaneous fill? etc. You can design for poor fill sites - just as you can design for poor "natural soil" sites such as muskeg, peat, etc. You just have to be conservative enough and have sound judgment.