A dispute was brewing between TransCanada and their tank erection contractor at the new Fort Hills pump station. The tank erector had designed and furnished all elements of the tank including the bearing plate, which is normal for tanks like this. Upon arriving at the site, they noticed large rocks in the sand that the earthwork contractor had used to build the tank pad surface, making it totally unsuitable for supporting the tank’s bottom plate. Corrective grading delayed the tank erector, starting the project off on the wrong foot.
As plates were added to the tank shell, the contractor noticed that they were not fitting as easily as they should have. Their surveyor noticed that places on the shell shifted slightly as the work progressed. The work proceeded slowly for other reasons as well. The contractor claimed that the tank pad was defective in ways more extensive than just the rocks, and implemented a costly releveling program. They notified TransCanada that they would claim extra payment and time because of the defective foundation.
Left unresolved, construction delays would jeopardize TransCanada’s ability to meet their contract obligations, damaging their reputation as well as incurring significant financial penalties.
TransCanada hired us to evaluate the data, assess the validity of the contractor’s claim, and help them keep the project moving forward. Data quality was a significant problem, making it impossible to perform reliable computations using just the Contractor’s data. We worked with TransCanada to hire a local professional surveyor and designed a measurement program that corrected the deficiencies in the Contractor’s procedures. With better data, we performed analyses that evaluated foundation stability under a range of tank shell loads.
It turns out that the Contractor’s bearing plate design placed the tank shell, the source of the load, very close to the plate edge. So close to the edge, in fact, that most of the plate was too far inboard to contribute any support. Despite the plate being a standard width, its position made most of that width ineffective and the foundation was failing because it was locally overstressed. The plate shifting was a problem with the Contractor’s design, not with the tank pad. And the good news was that once the tank was in service and some liquid was compressing the sand near the shell, the bearing plate would be much more effective. The problem was limited to just the erection phase and would not be troublesome for tank operation.
Putting Our Computations to the Test
The dispute came to a head during hydrotesting—when the newly-completed tank is filled with water to test the quality of the welds that join the tank plates. The tank erector asserted that the water load on the unstable foundation would cause a catastrophic failure. Our computations led to a different conclusion. Because of the heightened tensions, TransCanada hired our Chief Engineer to oversee the hydrotesting program in person. We analyzed survey and water height data in real time and rendered opinions about the tank’s stability at each step of the test.
Communication is always easier face-to-face. Our presence at the relatively remote site made us particularly effective for keeping the test moving forward. We graphed up the data that demonstrated favorable foundation performance, delivered strong conclusions in-person, and the project was back on track before we left the site. The tank erector dropped their spurious claim that the sand pad was the source of their problems, the tanks were placed in service as planned, and the threatened litigation was not mentioned again.