It looks like the City of San Francisco is adding a new tourist attraction to the city’s landscape. The Golden Gate Bridge, China Town, The Embarcadero, The Fisherman’s Wharf, Pier 39, Lombard Street just to name a few, will be joined with a new attraction so even more tourist can cram into the already jam packed city.
What I’m talking about?
The Millennium Tower, which was built just about 8 years ago, decided that the Leaning Tower of Pisa in Italy gets too much attention and fame. The Millennium Tower, which has sunk into the ground a bit and is leaning these days, had set its sights on usurping the tower at Pisa as the most leaning tower on earth. You know here in America if you are not the biggest, the strongest or the best, then nobody gives a hoot. That’s why we call the championship games in baseball the Word Series, the basketball finals the World Championship, although everybody knows that in other countries people play pretty good baseball and basketball too. So The Millennium Tower wanted to be the Most Leaning Tower on earth. The way things go, it has outdone the Leaning Tower of Pisa bigly… (Big-League Ha-ha-ha)
Everybody knows that The Leaning Tower of Pisa, the free standing bell tower, has been tilting ever since it was built in the 14th century. Over approximately the past 800 years the top of the structure has moved horizontally about 13 feet or 154 inches to be exact. In the past almost 10 years the Millennium Tower has leaned about 15 inches on top. If it continues like that, in the next 100 years it will reach the displacement of The Tower of Pisa. After that? It will have the title: The World Champion of The Leaning Towers! We will be the best in the world again! (You don’t have to worry about what will happen 800 years from now, but theoretically the horizontal displacement would be about 100 ft.)
What has really happened?
The 58 story concrete condominium building, said to be the heaviest building west of the Mississippi, was built on a landfill. There are two ways to build on a landfill to avoid excessive and uneven or differential settlement, which can create this type of leaning. Use a “Mat” foundation, which is a massive concrete footing occupying the entire foundation area of the building to spread the vertical-gravity load, (excessively used in the low lying, marshy areas in Texas) or use deep piles to reach the underlying bedrock for firm support. Neither system was used. The piles supporting the building did not go deep enough into the bedrock, in this case about 200 feet below the surface. Instead, the builders relied on piles that were driven into firmly compacted sand and mud about 60 to 90 feet below.
Who is at fault?
If the structural engineer followed the soil or geotechnical engineer’s recommendations and did not make calculation mistakes, it appears that the geotechnical engineer is on the hook.
In the meantime, values of the condominium properties are plunging and the lawyers are circling like vultures in the San Francisco sky…