The project site, the State Route 87 (SR 87) Landslide, located between about 45 miles north of Phoenix in the Mazatzal Mountains near Rye, Arizona. The field trip was led by Pancho Garza, Arizona Section Vice Chair, and Wayne Harrison, Arizona Section member. In addition to their AEG affiliation, both are with AECOM, the engineering firm hired to investigate the landslide and develop emergency and long-term mitigation in response to the landslide.
The project has been a local news story of much local interest since March 21, 2008 when after a series of heavy precipitation events, a landslide in a cut slope buckled an adjacent portion of SR 87 resulting in a week-long closure of the highway. Immediately after the landslide, the Arizona Department of Transportation and their consultants conducted an initial assessment of the damage and possible causes. Aerial photogeologic reconnaissance and surficial geologic mapping guided an extensive subsurface investigation of the local slide and the much larger ancient landslide which consisted of test drilling and monitoring instrumentation installations. Monitoring and instrumentation included slope inclinometers, vibrating-wire piezometers, wire-extensometers, deformation surveys, and time-domain reflectometry (TDR).
The group totaling about 30 people included a mixture of professionals and students including attendees from all across the state. Everyone met up early Saturday morning before piling into two 15-passenger vans. The hour drive to the site was spent getting to know everyone, and discussing various geologic features along the way.
The project site is located at an elevation of approximately 4500 feet in the Mazatzal Mountains which are located within the Transition Zone Physiographic Province. The Transition Zone province is a very jumbled and extremely interesting geologic area that lies between the relatively flat uplifted Colorado Plateau province to the north and the tilted Basin and Range province to the south.
The field trip included three stops at various areas with the project site with the group leaders providing explanations to the group. The first stop allowed attendees to hike up on top of a dual-tiered set of soil nail walls to get a good view of the various project features including the head scarp of the ancient landslide structure in which the recent landslide occurred and the various cut slopes, buttresses, drainages, and instrumentation included in the investigation and mitigation. The second stop involved a 12-foot multi-plate with water dissipaters underneath an embankment buttress. The third and final stop was at a rock buttress within the landslide completed as part of the mitigation measures. Here site plans showing boring, instrumentation, and cross section locations and interpreted slide limits and cross sections showing the landslide and underlying geology were presented. Also, an up-close inspection of the instrumentation used in the on-going monitoring was presented.
After a quick lunch, the group piled back into the vans and headed back to Phoenix. The group arrived in the early afternoon where the weary travelers got into their vehicles and headed home, mostly to cool off and rest I think. Most of the attendees found the trip and presentation very interesting and suggested more field trips. Overall the trip was a great success!
For more information on the SR 87 Landslide project, be sure to catch the upcoming presentation at the AEG National conference in September. Upcoming Arizona Section events include our regular monthly meeting tentatively scheduled the week before the AEG Annual meeting (anyone visiting Arizona on vacation is encouraged to attend) our annual Holiday Meeting, and in early 2010, our fifth annual Student Night that will be held at the campus of Arizona State University.