A chart obtained by KPIX reportedly now shows that this accelerated sinking started as early as mid-May, though work was not halted until over three months later.
Geotechnical engineer Robert Pyke told the outlet this week that the work should have been stopped months earlier. “Certainly by the end of June, it was obvious that there was additional settlement as a result of installing the casings and the piles,” Pyke noted.
"Any responsible engineer should have called a halt," he added, stating that he believes the continuation of construction for two more months caused more damage.
Pyke's criticism was leveled at Chief Engineer Ronald Hamburger, who pushed back in an email to SFGATE Thursday, stating that he became concerned with the increased settlement in early June. However, Hamburger wrote that he believed "additional settlement through completion of casing installation would not be a problem."
Hamburger went on to say that after settlement rates increased again in July, he recommended a moratorium on the installation of the larger 36-inch casings so the team could observe the effect of the work after installing only the 24-inch piles on Fremont Street.
"After a brief period, it became obvious that the 24-inch piles alone were causing undesirable settlement and we recommended and the homeowners immediately approved cessation of the work," Hamburger said. That stop finally came weeks later after pressure from the city.
The continuation of the work may have caused another problem in the building: sewage back-ups.
A separate San Francisco Department of Building Inspection report filed Aug. 27 — that SFGATE obtained — saw "evidence of water intrusion through the basement walls of the subterranean levels and signs of past settlement" from the tower's earlier sinking. However, these observations did not differ from a previous inspection in March.aside">
City Hall has criticized the work; in September, Supervisor Aaron Peskin called for a new independent review of the project.
Hamburger told SFGATE on Thursday that he maintains that the building is stable and safe, and the current work is not even needed from a technical perspective.
"The HOA has always made clear that although the voluntary upgrade was not required, it is interested in restoring the building’s reputation, damaged primarily by erroneous media reports," Hamburger said.
This reputation may also be affecting the value of the condos in the luxury high-rise. KPIX reported that 13 listings in the tower either expired or were taken off the market this year.
Work on the tower is now tentatively resuming, as engineers plan to drill two casings with a modified technique that should cause less vibration.
"The HOA is looking forward to the commencement of the pilot program," Hamburger said, "the results of which will determine the safest way to move forward."
Source : https://www.sfgate.com/local/article/sinking-millennium-tower-fix-too-late-16517457.php1230