The designer of the troubled fix of the Millennium Tower on Thursday declared a key first test of a new strategy to limit more sinking and tilting during construction a success, although experts and city officials cautioned the data was preliminary.
On Tuesday and Wednesday, crews completed installing a 36-inch diameter steel casing down 106 feet near the northwest corner of the tower -- where the structure has settled more than an inch since construction began on the fix in May.
The structure has now sunk at that corner some 19 inches, with the tower tilting more than 22.5 inches west toward Fremont and 9 inches north toward Mission.
The tower tilted more than 5.5 inches to the west since work to bolster the building on two sides started in May.
Fix designer Ron Hamburger told Millennium residents in a notice Thursday that the test was intended to “to demonstrate the Contractor’s ability to use improved procedures to install these casings without causing significant additional building settlement and tilting.”
“I am pleased to report that the test was successful,” Hamburger said. “Total building movement during the test was approximately one hundredth of an inch. This demonstrates that it is possible to install the remaining casings.”
He said a second test will follow, which involves installing a two-foot wide pile through an existing casing down to bedrock. “If this second test is successful, we look forward to a resumption of work and completion of the project.”
City officials, meanwhile, released weekly monitoring data showing that the building continues to settle despite a stop on work since Aug. 22, including an unexplained dip in early October indicating about the same settlement rate as measured before pile installation was halted in August.
Since fix work stopped, the building has settled at the northwest corner by about a tenth of an inch. That equates to three quarters of an inch annually – approaching the pace of the sinking that occurred when the tower was built.