engineers paused work for at least two weeks on the $100-million foundation upgrade for San Francisco's 645-ft-tall Millennium Tower high-rise residential condominium after measurements showed increased settlement during the installation of pile casings for the new piles.
设计升级计划的Simpson Gumpertz＆Heger的高级校长Ronald O. Hamburger的声明说，这项工作已被“出于谨慎的谨慎”而停止了两到四个星期。他解释说，暂停将于8月20日开始，将使工程师“更好地理解与增加的定居率相关的机制”以及减轻它的方法。
汉堡说，该建筑物仍然“完全安全”，没有受到伤害。
The tower settled about 17 in. since its completion in 2008. Work on the sinking 58-story building to prevent significant future settlement, financed by a court settlement, began last fall.
The pile scheme calls for transferring a portion of the building’s weight to bedrock from its existing foundation system. The fix, likened to putting a bumper jack next to a flat tire, relies on drilling and jacking 52 concrete piles—socketed more than 30 ft into the bedrock that starts 220 ft below grade—under the sidewalks of Mission and Fremont streets. Piles would support a new mat section, known as a collar, tied into the existing mat.
Shimmick Construction是堆积升级的承包商。
在工作期间，工程师一直密切关注建筑物的定居点，并在屋顶上倾斜。他们还一直在监视地面和地下水状况。传感器和测量设备收集数据和报告是由一家工程公司每周发布的。
Geotechnical Engineer John Egan, of SAGE Engineers, has issued a series of memos about what he has found after review of the data. In his June memo, Egan wrote that during the month in which the pile casings have been installed, "there has been settlement with the largest amount near Fremont Street where the casing work is being done."
埃根（Egan）理论上，在桩套管安装过程中，“桩钻机和插入和清洁钻壳的振动可能会在支撑塔的现有混凝土桩的尖端下方产生少量的海洋/Colma砂量的致密化。”
Marine sands are found in the San Francisco Bay area beneath the bay mud layer at depths between 35 ft and 65 ft. Colma sands are yellowish/orange and are found at depths from 35 ft to 110 ft.
The measurement of the building's position and tilt are being closely scrutinized with each phase of construction.
定居和屋顶倾斜变化
On June 14, Egan noted that the tower settlement rate had increased from roughly 1/8 in. a year to 1/4 in. a year starting in late January 2021 until early April. The increase coincided with the set-up and installation of the indicator piles. But the rate of settlement had been greater in prior years.
In the month beginning in mid-May when installation of the pile casings along the Fremont Street alignment was taking place, the average settlement of the tower has been about 1/16 in., or 7/8 in. per year, Egan reported.
埃根写道，自从11月开始建设工作以来，塔的倾斜也增加了。“与定居点相似……不同的倾斜度和速度增加与上述施工活动的各个时期相对应。”例如，“一项措施表明，屋顶层的横向挠度……向弗里蒙特街（Fremont Street）和大约to。朝米申街（Mission Street）略小于2½英寸。”
汉堡预测，一旦桩的安装完成，并且将负载转移到新的桩上，“该建筑物将经历大量改进，并开始恢复一年中发生的一些倾斜。”
