Safe Survey Topo of a Rockslide

By Ben Webb | sUAS Flight Technician

Geological hazards, such as rock and landslides, can be an unpredictable environment and may pose a safety risk both to the traveling public and those attempting to mediate the hazard. Slope instability is one of the factors transportation designers consider when finding the most efficient way through extreme topography. However, an aging infrastructure is susceptible to geological shifts along the corridor, which require identifying the cause for solution.

MoDOT has been proactive with its Innovation Slide Repair Techniques Guidebook for Missouri since 2011, with the goal of finding long-term stabilization techniques outside of the typical excavation method. Applying such design innovation begins with an accurate and safely acquired assessment of the conditions, which often takes its own kind of innovation.

So, when MoDOT wanted a new roadway design for an additional passing lane next to a steep embankment, with some areas 123% grade in drainage channels, TREKK provided a safe solution to acquire the needed survey data. TREKK deployed its sUAS drone system on a rockslide area that was showing signs of possible slope instability needed for a 150-foot cut along Route 65. The flight technicians deployed from areas safely out of harm’s way.

To obtain the existing topography, traditional surveying topo methods meant requiring a survey crew on unstable, high-grade areas, with loose rock and drop-offs, next to a busy highway. The environment was so steep it would have required repelling in some areas to get grade. Introducing additional friction with surveyors walking the area made it susceptible to additional slide, not to mention putting crews in a hazardous environment.

A fly-to-ortho-to-3D approach using TREKK’s in-house sUAS platform provided 3D stereo pairs and colorized 3D points from a non-invasive 300-foot altitude. Typical aerial acquisition would be Nadir, referring to the downward-facing viewing geometry of an orbiting satellite. The flexibility of the sUAS platform allowed flight mission planning software to increase the side lap to help capture the crevasses, culverts, ditches, drainage issues and possible overhang of the existing topography. This highly-detailed survey data helped design technicians identify the geometric characteristics of the slope.

TREKK uses sUAS bird’s eye capture on a variety of projects, allowing for a realistic view of the landscape from above using HD digital orthos. The ability to obtain imagery at 1 cm/pixel resolution provides high resolution orthos used for visual aid while mapping. The acquired flight ortho and 3D points can also be paired with traditional LiDAR that has a greater penetration through vegetation because of its 100,000 points per second capture and up to five returns per laser pulse. The acquired 360-degree data can be used separately or combined with other TREKK technologies.