Sunday, December 2, 2012

Sued for using "dry prep" Atterbergs method

In 2010 a concrete company (and their subconsultant geotechnical firm and construction materials testing lab) was sued by the homeowner.  Their house was exhibiting cracking.  The foundation slab was designed as a post-tensioned slab based on the geotechnical report by Louisiana Testing and Inspection (LTI).  The homeowner chose to sue LTI (via the concrete company that hired them) for failing to identify expansive clay soils and for using the "dry prep" method to perform plasticity lab testing in lieu of the more thorough "wet prep" method.  The wet prep method typically yields a PI a few points higher than the dry prep (i.e. PI=24 instead of 19), which can affect the perception of risk of soil movement as well as the foundation slab design parameter values.

Any lab using the dry prep method can be described as lazy.  I only allow wet prep in my lab.

It turns out that significant stripping and clearing was performed for this lot and subsequent investigation showed some expansive clay was present on the site.  An expert witness geotechnical engineer for the defendant  hypothesized that the Builder filled in a large tree stump and root bulb areas with fat clay, or that the widely spaced borings (1 or 2) simply just missed the zone of expansive clay (most of the site was low PI soils apparently) by pure chance.  The condition was chalked up as an anomalous condition that just did not show up at the drilled (explored) locations (boring logs).  He noted the circular pattern of the swelling condition as validation of the clay backfill theory.  There was no reference to plumbing leak or tests for leaks.

The trial court ruled in favor of the concrete contractor (and LTI) (defendant) because:

- the plaintiff failed to prove that LTI's conduct was the cause-in-fact of the house damage.
- the court found that LTI did not discover the swell potential by pure chance
- the court found that LTI did not improperly report testing.
- the judge found that the plaintiff failed to prove that another design would have been used, and that the swelling would have occurred anyway.

I have a feeling that if i was the expert witness for the homeowner there would have been a better argument for holding the geotech (LTI) responsible (i.e. for poor site characterization and design parameter selection instead of looking at wet prep vs dry prep).  They took the wrong approach by suing based on reported data (lab testing) instead of the overall characterization or design itself, but without more info i cannot really comment intelligently on the case.

The good news for geotechs is the court requires a notable burden on the plaintiff.  The court requires 4 things for a finding of standard negligence:

1. Was the conduct in question a cause-in-fact of the harm that occurred?
2. Did the defendant owe a duty to the plaintiff?
3. Was that duty breached?
4. Was the risk and hard caused within the scope of protection afforded by the duty breached?

LTI got off, but only because the homeowner and their team took a poor approach to this case.  LTI still lost money through the time they had to spend on this case, all for using a dry prep method in the lab.

3 comments:

  1. Thanks so much for sharing this information! I have been looking into learning more about geotechnical engineering! I didn't know there was so much to know! Can you tell me where I can find more? Thanks!

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    1. If you are implying you are trying to learn more from the perspective of someone who is not in the industry it is quite difficult. Geotechnical engineering is one of the specialty branches of civil engineering and the topic is deemed boring by most laymen so the industry tends to be secluded from the public. My purpose for this blog is to provide experiences for others to learn from (both geotechs and other project team members involved in design and construction). There is a hodgepodge of information out there on the internet so you can learn more with time consuming searches, you just have to look for it. ASCE's Geo-Institute has a magazine i enjoy reading.

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  2. Great post. Thanks for sharing. http://sub.co.nz/

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