A new robotic arm from the Swiss university ETH Zurich can construct solid columns from 30 tons of loose gravel and 74 miles of string, reports Curbed's Liz Stinson.

The columns produced by the robot are a product of a process called jamming, which crams loose objects (like gravel) together in a specific formation that makes them behave like a solid.

In the case of ETH’s project, the engineers programmed a robotic arm to deposit layers of rocks on top of each other. Over the course of four weeks, the arm carefully laid layer after layer of gravel building upwards until the columns reached over 10 feet tall. In between each level of gravel is a layer of string that helps keep the rocks in place.

With jamming, absolute precision is impossible, but the robot strives for it nonetheless. To ensure each layer of rocks is in the right position, the engineers designed the arm to be powered by computer vision, enabling it to calculate where each piece of gravel must go to build a stable base. In the end, the columns were strong enough to support an eight-ton steel roof—not bad for some rocks and twine.

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