Dock replacement:Cheaper approach approved for now
An alternative drilling method for installing the new pilings at Crescent City Harbor could save money, but harbor engineers have been skeptical about the approach.
A decision has been tentatively made to move ahead with the new method on the crucial component, which provides the structural foundation for docks by installing pilings deep in the basin bedrock.
The harbor was swayed with protective conditions including the contractor-chosen engineering firm backing the method with its liability insurance and conducting strength tests on the preliminary pilings.
The harbor’s original design called for drilling a 4-foot-wide hole for each piling, placing the 30-inch wide piling into the hole, and then filling the remaining space with concrete.
Dutra Group, the company awarded the inner boat basin reconstruction project, proposed a method of drilling 30-inch wide holes (same diameter as the pilings) and then vibrating the piling into the hole.
During a recent Crescent City Harbor Commission meeting, harbormaster/CEO Richard Young compared the methods:
“The analogue is putting a fence post in dirt. If you set it in concrete, that’s a pretty solid fence post. If you dig a hole and put it in the dirt, it might not be as tight of a fit,” he said.
The harbor’s engineering firm, Stover Engineering, and another engineer, Ben C. Gerwick, weren’t originally convinced of the structural viability of the second drilling method. Young said that the Gerwig engineers, however, started to put more faith into the second method after seeing more information from PND Engineers, a third engineering firm brought in by Dutra.
“I think the final straw is that they told PND engineering that they are going to have to own this,” Young told the commission. “If these piles fail below the surface it will come back on PND engineering. They have to put their liability insurance on the line and their faith and credit on the line if this fails below the rock line.”
If the pilings fail above the rock line, then it will be Stover/Gerwick’s responsibility, Young said.
The alternative drilling technique pushed by Dutra is supposed to be much faster, less expensive and it will have less impact on the bottom of the basin by displacing less bottom material, Young said.
The technique would be roughly $720,000 cheaper than the original method. The savings would be split between the harbor and Dutra. Since the harbor is paying 25 percent of the cost of repairing the damage to the pilings from the 2006 tsunami, the harbor would save around $90,000 with this method.
“Everyone’s nervous about it but Dutra’s confident, and PND is a very reputable, old-time engineering company,” Young said.
In an effort to build more confidence in the technique, Dutra and PND offered to first install five percent of the pilings and complete strength tests before installing the rest.
On Monday, Stover Engineering received a detailed plan of how the testing would be done through a cycling test.
Heavy loads replicating what would happen during a once-in-50-years tsunami will be put on the piling, then taken off, then put back on, over and over again.
The test should confirm the integrity of the alternative method, Young said.
A construction barge carrying the crane that will drill the holes for the pilings (regardless of the method used) will be leaving the Bay Area headed to Crescent City this week.
The barge was previously expected to be here by now, but Young said the project is not behind schedule.
“They have a finish-by date; not a start-by date,” he said, adding that Dutra will pay financial penalties if the project isn’t finished on time. “There’s no delay in the schedule.”
Piles of rock for protective rock slope walls have been delivered to the harbor, but there are concerns that the material might be too small. The smaller rocks will be mixed with larger rocks to maintain strength if necessary, Young said.
“Nothing will get installed that doesn’t meet specs,” Young said.
The parking lot at the northern end of the harbor has been saw cut in preparation for tear-out, but Dutra will not demolish the lot until the appropriate rock slope material is delivered.