A meticulously programmed excavator can autonomously construct walls from natural stones. According to Swiss researchers from ETH Zurich’s report in the journal Science Robotics, the robot surveys the available boulders, measures each one, and determines the best placement for each stone. Subsequently, the twelve-ton excavator, equipped with a kind of gripper arm, places stone upon stone.
In a field trial, this process resulted in a 10-meter-long and 4-meter-high freestanding dry stone wall composed of 109 boulders. The excavator utilized both broken concrete pieces from demolished structures and natural rocks. Additionally, the robotic vehicle assembled an approximately 65-meter-long wall along a small slope. “The work demonstrates the potential of autonomous heavy construction vehicles to be built with highly irregular, readily available, and sustainable materials that require minimal to no transport and no prior processing,” writes the team led by Ryan Luke Johns.
According to a university statement, the excavator first creates a 3D map of the construction site using sensors and identifies the stones present. It lifts them individually and scans them to determine their approximate weight and center of gravity. Subsequently, an algorithm determines the best position for each boulder. The excavator then places each stone in the correct location. In one operation, the excavator robot can extend the wall by 20 to 30 stones.
The autonomous excavator is currently relatively slow. To place a stone, it takes 12.2 minutes, approximately 1.2 minutes longer than experienced human excavator operators, according to Johns’ team.
The researchers emphasize that building with natural stones and demolition remnants could be a more environmentally friendly alternative to concrete construction. “Conservatively estimated, the construction of such a wall could save around 41 percent of carbon equivalents compared to a similarly efficient reinforced concrete wall,” the team writes. Moreover, the wall constructed by the robotic excavator could be disassembled into its individual parts and reused.
The researchers have envisioned various applications where the robotic excavator could be employed, including coastal protection structures.
Taking it a step further, the group introduces the possibility of deploying such an excavator in an “extraterrestrial context,” such as on the Moon. “In space, resources are scarce, transport is expensive and energy-intensive, and there is an extreme shortage of skilled craftsmen,” the study notes. Therefore, developing automatic systems that can utilize existing resources is deemed prudent.