Documents that could shed light on causes behind San Francisco's rapidly leaning Millennium Tower either never existed, or were already reviewed by the chief engineer Ronald Hamburger. Either way, the building, and its contractors aren't turning them over to SF Supervisor Aaron Peskin.
The city now has a regulation about this sort of reporting but did not at the time of the drilling in question.
"I want to see that information, I want our experts to see that information — they need to produce that information," said Supervisor Aaron Peskin, referring to the now missing drilling log data from when six foundation support piles were drilled and installed back in August, when the building was sinking and tilting so fast that it prompted a halt to the fix.
Peskin first pressed fix engineer Ron Hamburger about the issue during a hearing last week.
"There was no requirement that they be furnished to the Department of Building Inspection," Hamburger told Peskin. "There was a submittal made to me as engineer of record. I reviewed it, returned it to the contractor as approved."
City building permit director Neville Pereira backed Hamburger on that assertion, agreeing there was no city requirement in place at the time.
As usual, there is nothing to worry about here as Ronald Hamburger "reviewed it," but it seems like the data is hoped to answer a question of "where did the tons of extra grout go, and why was it needed?" It seems like Hamburger was characteristically unconcerned with the tons of extra building materials that were unexpectedly needed to fill in a huge hole in the ground below a rapidly tilting building.
The drilling logs are of particular interest because an independent expert's report pointed to apparent problems during the drilling of two piles at the time when the building was sinking and tilting more rapidly. In his analysis of the first test pile installation, Ben Turner of Dan Brown & Associates told Pereira in a report that some of the data he reviewed suggested a theory that pile installation crews "unintentionally mined'' ground beneath the building.
He noted that in two cases in August, construction records show crews had to pump in far more than expected amounts of concrete grout to seal up the pile installation holes. Turner first suggested the grout was filling voids created when soil was removed during drilling.
At the hearing, however, Turner said the current theory is the ground simply absorbed the tons of extra grout.
Meanwhile, Peskin says he's left frustrated by the gap in information at a key time in the project.
"Mr. Hamburger said on the record that the data did exist — although it says somewhere else that the data does not exist," Peskin said Wednesday. "If it exists, I want it."
