A Sustainable Workforce Starts With You

That Sinking Feeling

It is that sinking feeling that you get in the pit of your stomach when you realize that a project is “going south” and that you are headed for arbitration or a lawsuit. Then imagine how you would feel if the fix for the problem is estimated to be in the $150 million range on a project whose original budget was $350 million.

That is the case for the “Leaning Tower of San Francisco,” the Millennium Tower, that we have written about several times on Construction Citizen. Lawsuits are flying and the building continues to sink and list.

There is more to the story though in the City by the Bay. Recently ENR published an article titled “Supertall Survivor” on the construction of Salesforce Tower, the 1070-foot-tall office tower that is a neighbor to Millennium Tower. They both frame the Transbay Transit Center recently renamed the Salesforce Transit Center. The ENR article details the structural solution for the tower that is designed to withstand a major earthquake with a new design known in the structural world as a “quiet building.”

The Salesforce Tower and the Salesforce Transit Center projects were developed by Houston based Hines, designed by Pelli Clarke Pelli and architect of record, Houston based Kendall/Heaton Associates Inc.

Across the street the Millennium Tower continues to sink at a rate much higher than expected. Residents of the pricey condo tower have filed a lawsuit against the City of San Francisco claiming that the de-watering of the Salesforce Transit Center caused the soil to lose its bearing capacity thereby creating the problem for the tower, developed by Millennium Partners in New York City.

The ENR article states, “The (Salesforce) building team also had to deal with poor soil conditions. From the top down to weak bedrock, more than 250 ft. below grade, there are layers of dirt filled with debris, sand and then clay.”

The article continues, “There is potential for the liquefaction of the soils” in a quake, says Jeffrey Dunn, a principal of the project’s engineer, Arup, which also is the geotechnical engineer for the multimodal transit center and 181 Freemont, a high-rise nearby. If soils liquefies, it loses capacity to support a structure, says Dunn.”

The major difference between the two structures is that the engineers and developers of the Millennium Tower built a foundation system of piles that extend roughly 68 feet deep, resting on Colma clay, not bedrock, while the foundation piles of Salesforce Tower extend up to 310 feet deep into bedrock.

According to the studies of the Millennium Tower problem, the ultimate solution is to drill 50-100 new caissons down to bedrock to stabilize the building at the $150 million cost stated above.

Meanwhile, the Millennium Tower lawsuits remain unresolved and the “Leaning Tower of San Francisco” is still leaning.

The ENR article tells an interesting tale of the development and construction phases on the tallest building in San Francisco, Salesforce Tower, currently 90% preleased.

Thanks to Nadine M. Post, editor-at-large at ENR for the article.