Mission Profile Sinkhole Eval

Dangerous and dirty, but not at all dull.

- Patrick Sherman

PILOT REPORT: Almost from the beginning, one of the most compelling arguments for the use of drones and other robotic systems has been that they can replace humans doing jobs that are dull, dirty, and dangerous. When I was called out by the Department of Public Works in Clark County, Washington, this past winter, I was confronted by a mission that checked two of those three boxes and that tested my limits as a pilot like no other.

What I will describe as a “sinkhole” opened up under a local roadway. When the road was built during the 1920s, engineers laid down concrete panels underneath the asphalt surface that is visible today. Now, owing to that layer of concrete, the road itself had not collapsed but, instead, had formed the world’s most poorly engineered bridge spanning the void.

Carolyn Heniges, the road operations division manager, describes what had happened: “There was a culvert under the road, which failed in some way. That allowed water to escape, and it started washing out the soil underneath the road, until it eventually blew out.”

From the surface, nothing appeared to be amiss, except for a guardrail support post suspended in midair off to one side of the road. The damage was discovered by a road crew, doing inspections after a winter storm moved through the area.

“These guys are really sharp,” says Mike Lewis, the emergency management coordinator. “They know their roads really well.”

On Heniges’ order, the road was immediately closed, and for good measure, she had concrete Jersey barriers brought in to completely block passage.

“We’ve had problems in the past when we close roads,” she says. “People will get out of their cars and pull wooden barriers aside, then drive through. In this case, that could have led to a life­threatening and potentially tragic ending.”