When I was doing environmental due diligence, I looked at a one-story law office building on Alameda, across SF bay from San Francisco. The island that Almeda is on is basically a big sand bar. The owner of the building told me that he had to drive pilings down 100 feet through the bay muck to reach bedrock. That was for a ONE story building and that if he didn't it would have sunk over six inches in 10 years. What the hell were they thinking when they only went down 80 feet for one of the biggest buildings in San Francisco?
San Fran has been around since 1850. There were numerous old buildings at those locations over the years. On the location of another residential high-rise less than a half mile away, they found the foundations of a sailor's convalescene home and a ship salvage yard, both dating from the end of the 19th century.