On March 21, 2008 a landslide caused the closure of Arizona State Route 87 between Payson and Phoenix near mile post 224. So far there are no official estimates as to the size, but based on aerial photos, it appears to be at least 50,000 sq-ft in plan. The offset at the head scarps was approximately 2-meters (6.6-ft) according to AZGS Geologists on site. It appears to have been a rotational slide as the toe of the landslide heaved the southbound roadway up by as much as 1-meter (3.3 ft). There was an existing soil-nail retaining wall on the slope that was destroyed by the slide as well.  Lateral deformations can be seen in photos of the median barrier and the roadway striping. The deformations extended into the northbound lanes as well. More photos and links after the break. (Photo by ADOT)

(Photo by ADOT) 

(Photo by Brian Gootee, AZGS)

From very early on the Arizona Geologic Survey or AZGS has been very active in assisting ADOT in analyzing the slide. More information and a preliminary report can be found on AZGS’ SR 87 Landslide page. The Arizona State Geologist, Lee Allison has also been reporting on the slide at his blog, Arizona Geology. On that blog, he discussed a 1995 USGS report issued to ADOT covering the geology of the new SR 87 alignment. In that report, the author, Clay Conway, mapped a landslide deposit 120-ft thick in close proximity to this slide (see the map at Lee’s blog). There does not appear to be much information in that report though that would be useful for engineering analysis. (Photo by ADOT)

Mimi Diaz of the AZGS at the head scarp of the slide (Photo by Brian Gootee, AZGS)

No word yet on what ADOT plans to do to stabilize the slope, if anything. Based on past problems in that corridor, and on photos from AZGS, it appears that they have opted to simply lay back the slope to a shallower angle, a perfectly acceptable engineering solution (if it works) if not the optimum one from an aesthetic perspective. Whether that is a temporary or permanent solution remains to be seen.

According to ADOT, the highway has been re-opened as of today, March 27. They have a single lane open in each direction, in the northbound lanes (farthest from the slide). They likely will have additional work to do to repair the damaged roadway. We’ll post more updates as they come in.

Sources for Photos:

• AZGS SR 87 Landslide page

• Lee Allison’s Arizona Geology Blog

• Photos by AZGS Geologist Brian Gootee at Pbase (Brian and AZGS Phoenix Branch Chief Mimi Diaz have been performing the geologic reconnaissance of the landslide for the AZGS)

Related Items:

• 105th Anniversary of Frank Landslide
• ADSC Joins with FHWA to Conduct Hollow Core Soil Nail Research
• Allegations: Oregon Not Forthcoming With Landslide Hazard Information
• Arizona Earth Fissure Planning Maps
• Arizona Geologic Survey Releases Earth Fissure Maps

• Schnabel Foundation Company
• Arizona Wells
• NCS Consultants, LLC
• Saguaro GeoServices, Inc.

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