Opinion: High-Rises Won't Sink San Francisco

John A. Egan and Ronald O. Hamburger, in a piece for the San Francisco Chronicle, challenge a recent article in the same publication that claimed the San Francisco Bay area is literally sinking under the weight of high-rise development. The article's "alarming language suggests that this is a sudden phenomenon, and that San Francisco, in particular, is at risk of sinking underwater as bay fill is compressed by the weight of the skyscrapers that rest upon it." The authors argue this is an exaggeration of dynamics that are neither new "nor among the serious threats to coastal areas from global warming." 

Since at least the 1930s, civil engineers have been aware of the settlement performance of buildings and the potential for subsidence in downtown San Francisco, where parts of the shore were filled in more than a century ago. But most buildings are anchored farther down than the infill layer, and the effects of "differential settlement" don't stretch far beyond the building itself, according to the authors. Millennium Tower, one of the buildings highlighted in the prior article for its effects on the soil, "is supported by a foundation with nearly 1,000 concrete piles that extend beyond the fill into dense sands about 80 feet below the ground" and is undergoing an additional upgrade with new pilings that will anchor it even deeper. "Despite the dramatic numbers scenario outlined in the Chronicle piece, we advise caution about settlement predictions that are based on the aggregate weight of urban development."