Millennium Tower is built on landfill prone to liquefying

Is Millennium Tower actually going to fall over?

Well, Stanford’s seismic center (which does of course spend a lot of time pondering the possibility of local building collapse) says no. At least, not right now.

Even after moving a combined 18 inches west/into the earth from its original position, it takes more than a stiff breeze to topple a 58-story skyscraper, however inadequately moored.

Such a building may eventually shift to the point that it represents a danger to its structural integrity. But even though its present rate of engulfment is fairly alarming, it’s not going down fast enough to take anybody by surprise.

However. The presence of a seismic center at Stanford in the first place reminds us there is always our ticking geological clock to consider. The Millennium Tower is a reinforced concrete framed building. In fact, it’s the largest concrete building in a seismic zone of this caliber.

(Over the years, a lot of time and money has gone into making concrete a more suitable seismic building block.)

USGS

And where does this enormous, dense, heavy concrete building sit? As the earthquake site Temblor points out, right on top of a big pile of fill-in land. That makes it highly vulnerable to the risk of liquefaction.

Liquefaction happens when the shaking of an earthquake briefly causes loose soil to behave like liquid. (Or sometimes just when shaking pushes actual liquid water too close to the surface.)

Of course, things will go back to normal when the shaking stops. But that’s too late for whatever structure used to sit there. For one harrowing example, look at the Marina after the 1989 Loma Prieta quake

In fact, Temblor points out that liquefaction may be a big part of the reason the building has tipped in the first place. A building this size weighs hundreds of thousands of tons. That’s a lot to ask out of land that doesn’t have much integrity of its own.

Of course, you don’t have to worry about that as much if you just fix your building to the bedrock 200 feet below, underneath even what used to be the ocean floor. Which they didn’t do.

But what’s the worst that could happen, right?

• The Leaning Tower of SF [Temblor]
• Tower in SF Has Sunk [NBC]
• Millennium Tower [Concrete Reinforcing Institute]
• What If Concrete Was Made Ductile? [Structure Magazine]
• What Is Liquefaction? [USGS]
• Liquefaction Map [USGS]