Largest dry-stone wall built by a robot

The largest freestanding dry-stone wall constructed by a robot measures 10 m long, 1.7 m wide and 4 m high (32.8 ft x 5.6 ft x 13.1 ft). It was constructed in Zurich, Switzerland, by a robotic excavator called HEAP (Hydraulic Excavator for an Autonomous Purpose), which was the work of a group from the Robotics Systems Lab (RSL) at ETH Zurich. The automated stone construction method was developed at Gramazio Kohler Research and the RSL, by Ryan Luke Johns (USA) and Martin Wermelinger (Switzerland). The details of the project and team were published in Science Robotics on 22 November 2023.

HEAP is based on a Menzi Muck M545 12-tonne walking excavator, and can be fitted with either a grasping arm for assembling walls or a digging bucket for grading a site.

When activated, HEAP uses LiDAR scanners to examine its worksite, mapping the contours of the terrain and making note of any potential building materials. Its on-board AI has been trained to recognize rocks and demolition debris that match the approximate size requirements it has been given.

HEAP first picks up each rock and rotates it in front of its primary LiDAR scanner, creating a 3D model of the stone and an approximation of its mass. Once it has a detailed inventory of its building materials, HEAP maps out roughly how these varied stones could tessellate together to create the strongest possible wall, matching the dimensions it has been given. It then places the stones one by one into the wall, updating its model with continually updated scans of the wall's top surface.

The autonomous excavator is designed for "infrastructure-scale" construction – large stone structures such as seawalls and terrain stabilizing retaining walls. The average weight of the stones it used to build this wall was over a tonne. After constructing the freestanding wall as a proof of concept, HEAP was used to build a 65 m (213.3 ft) long and 6 m (19.7 ft) high retaining wall as part of a public park in Oberglatt, Switzerland.