The Department of Public Works has installed $8,700 worth of boulders as a defense against homeless “re-encampment” underneath the tangle of freeway overpasses at Cesar Chavez and Potrero Avenue known as the Hairball.

More boulders are on their way.

“We put them in there to help deter re-encampment a bit and for aesthetics, just to change it up,” said Larry Stringer, deputy director of operations at Public Works.

In November, the city cleared a sprawling encampment at the Hairball that had persisted there for years. At present, only a few homeless residents remain under the overpass, while others have moved to surrounding sidewalks.

“It’s more cost-effective than what we were doing,” Stringer said, referring to the weekly cleanups Public Works performed before the encampment was cleared. “We were doing cleanups three or four times a week to keep garbage out.”

Public Works will continue to install the boulders over the next month, Stringer said.

“That is just typical anti-homeless landscaping,” said Kelley Cutler of the Coalition on Homelessness about the boulders.

She compared them to the highly criticized “anti-homeless” spikes that were being installed throughout London. “This is simply the same thing, but with boulders,” Cutler said.

The strategy isn’t new in the United States. Similar strategies have been criticized in San Diego, and more recently — like this week — in Seattle.

In July, redesign plans for the San Francisco Library’s Castro branch faced criticism for employing “defensive design,” which included hard rocks, spiky plants, and metal railings on the library’s exterior.

After a homeless encampment was removed in 2013 under Interstate 280 freeway near the downtown Caltrain station, Caltrans installed $300,000 worth of fencing to keep campers from moving back.

Walking through the Hairball recently, it became clear that some of the boulders were placed strategically, while others were clustered in certain areas, leaving plenty of room for people to occupy.

Stringer said that boulders are now being “stockpiled” in certain areas and will be relocated throughout the property.

Robin Walter, who has been sleeping in a tent at the Hairball, said she noticed the Public Works crews start installing the boulders two and half weeks ago.

“It’s stupid,” she said. “You could still put something there, and two of us could easily move them.”

Stringer said there are no penalties for tampering with the boulders, but California Highway Patrol — who has jurisdiction over the Caltrans-owned land — could issue citations for trespassing on the property.