huangyhg

soil boring & testing alternative
because soil boring and sample testing are relatively expensive for determining how deep drilled piers should be, contractors sometimes drill a test hole as a cheap alternative. the correct depth is estimated by simply noting the type of soil coming up as a function of drilling depth.
is this practice effective? it would seem that much information is missing and that there is much at risk.
i would agree that this is risky.
soil testing in my area runs from $2000-$5000 for most of the buildings i am involved with. the higher prices are for larger buildings (require more test holes) or for buildings that fall into the essential type category (hospitals, etc.). these projects run from $500,000 to $15,000,000. the cost of doing soil exploration is negligble when compared to the overall cost.
if i was in a position that i would have to follow the procedure you are asking about, i would find the geotechnical engineer who has done explorations in the vicinity and this still would make me very nervous.
perhaps your question would work better on the soils testing engineering forum:
soil borings are cheap insurance and money well spent (i.e. cheaper than a lawsuit). i would never take on a foundation design without this information, not even a residential structure. if it means that i don't get the job, so be it.
good luck
if contractors do this they are taking all of the risk for the performance of the foundations. if that is a risk they are willing to take, then go for it. if not, they should hire a qualified professional geotechnical engineer to perform a geotechnical evaluation.
thank you all for your replies. i agree. at least one city in our area requires that a pe design the corrective measures for a slab foundation repair permit to be issued to the contractor. a contractor should not be allowed to install a belled pier system without it being designed and installed properly. the design should be based upon a geotechnical evaluation.
i would not design a structure without a soils report. man, soils are tricky even if you get soil borings. in a case near me, tank designer/builder only took one boring to 100-foot depth under a 5 million gallon tank. the tank is sinking and if more holes, and deeper, would have revealed a layer of clay!!!!
cost of drilling is peanuts compared to cost of litigations and trying to fix structures.
my two cents worth
lutfi

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