INSTRUMENTATION OF THE DEBEQUE CANYON LANDSLIDE AT INTERSTATE 70 IN WEST CENTRAL COLORADO

The DeBeque Canyon landslide is located 34 km east of Grand Junction. The Colorado River formed the canyon by eroding into a plateau of gently dipping Mesa Verde Group Formation. Interstate 70 follows the river and crosses the landslide toe on the south floor of the canyon. The historical record of this landslide dates to the late 1800s. Catastrophic movements occurred at the turn of the century when the slide toe entered the Colorado River, damaged the railroad and flooded structures on the opposite bank. In 1958, the landslide toe heaved the highway 7.3 m during a road-widening project. Another major re-activation in 1998, heaved the roadway 4.3 m vertically and 3 m laterally, badly damaging the Interstate. In response to that event, a multi-agency task force was formed to conduct a detailed investigation of the landslide. Part of that investigation was focused on the development of a comprehensive instrumentation program.

The program was designed for emergency notification and long-term monitoring. Automatic tools including extensometers, tiltmeters, inclinometers, a rainfall gage, and rockfall warning fences are wired to two cellular-based data collection stations. Manually-read instruments, including inclinometers, piezometers, and manual extensometers were also installed. An array of prisms, anchored to rock faces, and GPS points are periodically surveyed. In the event of a significant movement and/or rockfall event, the respective dataloggers are programmed to send an alarm.

The slide complex includes block glide, translational, and deep rotational movements. Of primary concern is a 44,000 m² by 90 m thick block of fissured, flat-lying, massive sandstone and thin shale, that is moving on an underlying weak shale bed toward a rubble zone at the valley bottom that has created a deep graben-type fissure at the headwall. If this block were to move catastrophically, the highway corridor could be cut and the Colorado River again partially blocked.

The landslide has been monitored for four years. The collected data show continual creep in the upper landslide mass, even during the extremely dry conditions that Colorado is experiencing today. Movement rates generally increase in the winter and slow during the summer. Since the 1998 event, no movement has been detected at the roadway.