San Francisco’s Millennium Tower is the tallest building in the city at 58-stories, filled with luxury condos inhabited by some very annoyed people. The building has gained a reputation as the “leaning tower of San Francisco” since is was revealed earlier this year that it’s started sinking and tilting. The building developer has claimed that the sinking was slowing and would stop soon, but a new satellite analysis from the ESA says otherwise. If anything, Millennium Tower appears to be sinking even faster.
This residential skyscraper cost more than $350 million to build, and he most expensive penthouse condos sold for around $12 million. However, the city of San Francisco now alleges Mission Street Developers LLC cut corners and did not properly disclose the structural issues to owners of the condos. The building has sunk approximately 16 inches downward, and there’s a northwest tilt of 2-inches at the base and 6-inches at the top. Some in San Francisco say you can see the minor tilt from a sufficient distance away, but that might be confirmation bias.
The European Space Agency (ESA) decided to conduct observations of the San Francisco Bay area because it includes the earthquake-prone Hayward Fault. The analysis was conducted with the ESA’s Sentinel-1 satellites. There are two of these satellites in orbit at an altitude of 400 miles. The goal of Sentinel-1 is to track urban ground movement and fault activity around the world using radar, particularly subsistence hotspots in Europe. That also means it can take very accurate measurements of the Millennium Tower.
The image above uses colored dots to show change over time from the satellite’s perspective. The red dots at the top of the tower indicate it has moved nearly 40mm away from the satellite. Overall, the ESA estimates the tower is sinking at a consistent rate of 1.6-1.8-inches per year. That’s much faster than previous estimates on the ground of 1-inch per year. It’s also not slowing down, as Mission Street Developers has insisted.
This tells us the scale of the problem, but not the cause or solution. Engineers have speculated that Mission Street Developers made a mistake using friction piles to anchor the building. There are 950 of them driven 60-90-feet into the ground. They don’t reach all the way to the bedrock, but other buildings in the city use similar designs. The Millennium Tower is much larger, though. The developer claims the tilt is all the city’s fault. It says work on a nearby railway station may have removed groundwater that changed the consistency of the ground under Millennium Tower. Whatever the reason, the new ESA data gives residents of Millennium Tower more to worry about.