Putting 900 Pounds of Explosives Below an Abandoned Suburb For Science

It's not every day that the average person gets to blow something up at their job. Even rarer: Getting to blow up the neighborhood where you used to live. But as Next City reports today, that's exactly what happened to the last remaining resident of an abandoned suburb that served as the testing ground for an experiment that may lead to safer, more earthquake-proof buildings.


The earthquake that hit Christchurch in 2011 destroyed thousands of buildings, but it also rendered hundreds of whole neighborhoods uninhabitable because of "soil liquefaction," a phenomenon that makes the structures above it prone to collapse, as commenter Yuppie Scum explains much more clearly here.

Illustration for article titled Putting 900 Pounds of Explosives Below an Abandoned Suburb For Science

The results of soil liquefaction in Japan in 2011. AP Photo/Lee Jin-man.

Earthquake experts from around the world, led by The Earthquake Commission, wanted to test a structural system that would fight liquefaction by stabilizing the soil, and they chose one Christchurch suburb to install a prototype. And then blow it up.

The team embedded 900 pounds of gelignite—a type of explosive invented by Alfred Nobel—below their structural system, which had been installed below the chosen abandoned Christchurch suburb. Then, in an act of poetic symmetry, they enlisted one of its old residents to press the button—and off it went.

NextCity has the scoop on the results of the project, which sound promising:

While about $8 million was spent conducting the trials, Cowan said the research could save untold billions in the future. Not only are the researchers learning how to reinstate damaged property, but also about preemptive actions that could help cities avoid huge costs in the event of a disaster.

The methods appeared to work. The liquefaction that was produced after the explosions seemed less intense than without the stabilization system. The columns confined the effects of liquefaction, and the denser ground meant the houses appeared to be stable on the earth.


In fact, this isn't the first time scientists in New Zealand have created explosions to simulate the terrible earthquake that hit the country. In 2011, a team of researchers blew up a damaged stadium to create a similar shaking, all in order to put several new types of foundation designed to withstand liquefaction through their paces.

Sometimes to rebuild, you have to tear it down. Or blow it up. [NextCity]



Yuppie Scum

"soil liquefaction," a phenomenon in which heavy topsoil presses on softer soil below it, creating instability and making structures above it prone to collapse.

Not quite. Think of filling a glass with sand, then filling it with water, and then shaking it from side to side. When the shaking occurs, the sand will "float" around and lose its ability to bear any load- behaving similar to a liquid. Once the sand settles, it can bear a load again.

If you have a buoyant object contained within the soil when it is in its "liquid" state, it can float. Conversely if you have a a non-buoyant object, it can sink when the soil is in a "liquid" state. When the soil resumes properties of a solid after the shaking has stopped, everything is then locked in place.

For once, the wikipedia article isn't terrible:


Source: me - structural engineer