Hindsight About Unforeseen Site Conditions
Interpreting Subsurface Information:
Why Borings Are Not Boring
By: Doug Shevelow, P.E.
Reprinted from November 2006 ohioconstructionlaw.com
Boring logs are the best tool to determine the engineering properties of the earth's subsurface. But boring logs represent only a tiny fraction of the subsurface. They also must be interpreted. And small differences in interpreting a handful of boring logs may lead to significant differences in how a contractor views a project.
It seems only natural for an incautious bidder on a complex construction project to be prone to interpreting project data in ways that minimize costs, resulting in a lower bid and a better chance of winning the job. But wise bidders know this type of mindset can lead to disaster if all that bidding optimism turns out to be without foundation.
A recent differing site conditions case from the Board of Contract Appeals for the General Services Administration illustrates this
lesson and provides some useful rules for interpreting subsurface information provided by the owner.
The case, PCL Construction Services v. General Services Administration (GSBCA 16588), involved the construction of a federal courthouse in Cape Girardeau, Missouri, using the design/build project delivery method and negotiated procurement. The contract included the standard differing site conditions clause from the Federal Acquisition Regulations, granting relief for Type I (different from the plans) and Type II (highly unusual) site conditions.
The geology underlying the site was complex. The government provided all proposers with a geotechnical report that indicated the presence of voids, weak zones of unconsolidated materials, and weak zones of bedrock, and warned of the potential for sinkholes. The government’s geotechnical report recommended that additional borings be taken before a foundation was designed.
The contractor hired its own geotechnical consultant. Using the government’s report, the consultant designed a foundation for the building that used drilled piers. The contractor’s geotechnical engineer took a more optimistic view than the government’s engineer. Where one of the government’s borings was terminated at a shallow depth, the contractor interpreted this as an indication of shallow, competent bedrock, meaning that the drilled piers would not have to be as deep. But as it turned out, this was indicative of a large boulder or a rapid peak of bedrock, instead.
Where one boring was terminated after drilling through eleven feet of weak bedrock, the contractor’s engineer estimated that competent bedrock was only three feet deeper. In reality, competent bedrock was much deeper. Another time, the contractor, ignoring several borings further away from the courthouse’s footprint, calculated that the average depth of incompetent bedrock across the site was 2.56 feet, then rounded this number down to 2 feet even. In reality, the average depth of incompetent bedrock was over 9 feet.
The greater thickness of incompetent bedrock and greater depths of unconsolidated material in the subsurface meant that the contractor had to drill its piers deeper and at a larger diameter, increasing its costs by nearly one million dollars. The contractor made a differing site conditions claim.
The contracting officer denied the claim, and on appeal the Board of Contract Appeals for the General Services Administration affirmed. Neither the contracting officer nor the Board thought the contractor’s interpretation of the boring logs was reasonable. The Board pointed to the recommendation in the government’s geotechnical report that additional borings be taken and the report’s repeated warnings of the potential for the bad conditions actually encountered. The Board was also troubled by the contractor’s selective calculation and rounding down of its estimated thickness for the incompetent bedrock.
The Board offered several points of advice for contractors to consider when interpreting subsurface information as part of compiling their bids:
Whether the borings are well spaced or few and far between;
Whether the boring logs are internally consistent;
Any warnings provided by the owner, as well as known hazards of the particular geologic setting; and
Whether the borings are inconsistent with other subsurface information.
The Board thought there were plenty of red flags both in the boring logs and accompanying narrative, but that the contractor ignored each one, and so it was not entitled to additional money.
The contractor had another big problem. To prove a differing site conditions claim, a contractor must have relied upon the incorrect
site information when formulating its bid. But in this case the Board determined that the contractor did not even solicit subcontract proposals for
the drilling and construction of the piers until after it had been awarded the contract. Again, this case illustrates a variation of what they used to say about marriage: Bid in haste, regret at leisure.
