What a mess! Dirt and water everywhere.
In June of 2014, two days of rain—11 inches of water—led to the collapse of 100 feet of a slope along the Mississippi River.
As we’ve been learning, there was no specific thing that caused this slope failure, but heavy water accumulation seems to commonly trigger landslides. The frequent use of this area—about 7,000 motorists and 1,000 bicyclists daily certainly contributed to its collapse. Other factors include (but are not limited to) the relatively steep angle of the slope, the poor water drainage of the soil, decreased slope stability due to the effects freeze/thaw cycles have had on rock and soil, and weakened bedrock.
Afraid of heights? This repair crew worked from some tricky angles..
Repairing the slope was a delicate and complicated task. Not only was short term monitoring immediately necessary, but long-term monitoring would prove to be crucial for a lasting fix. Immediately after the slope failure, one of the University of Minnesota's Fairview Medical Center’s buildings was evacuated by employees as the building itself was at the top of the slope and about 150 feet away from the site that collapsed. These nearby school buildings were assessed for structural integrity before further action was taken. The roads were cleared of debris a couple days after the slope failure, and a geofabric barrier was placed on the newly exposed soil to prevent further erosion and collapse.
This covering prevented more landslides from occurring while work was in progress.
The project took longer than initially expected due to Minnesota weather and other, less expected obstacles (like a 100-year old wall footing that was unearthed during construction), but the area was reopened in 2016. Long term fixes—completed with “low-vibration installation techniques” and constant monitoring—included putting in place new soil, new plants, 5 retaining walls, new drainage systems, and, as of 2018, plans to map out landslides.
The completed project! Notice any differences from the first photo?
Hennepin County commissioned an “atlas” to identify and track occurrences and warning signs of landslides. The atlas will enable better mitigation of these hazards and increase education around landslides. In fact, after Hennepin County’s effort was announced, different universities in four parts of the state expressed interest in similar projects!
Sources used:
Barr Engineering Co. (n.d.). West River Parkway landslide slope repair: Monitoring and stabilizing a slope failure provides safe parkway access. Retrieved from https://www.barr.com/projects/2327138700
Chanen, D. (2018, Jan 13). Twin cities' unlikely experience with landslides gets attention in washington. TCA Regional News Retrieved from http://ezproxy.macalester.edu/login?url=https://search-proquest-com.ezproxy.macalester.edu/docview/1987013935?accountid=1220
Holmstadt, J. (2016, September 26). Slope Failure. Retrieved from https://www.wsbeng.com/wsbpedia/blog/slope-failure
Kraker, D. (2014, September 02). Mudslide to keep West River Parkway closed until next summer. Retrieved from https://www.mprnews.org/story/2014/09/02/mudslide-to-keep-west-river-parkway-closed
Renault, M. (2014, Jun 25). Heavy rain causes west bank mudslide. University Wire Retrieved from http://ezproxy.macalester.edu/login?url=https://search-proquest-com.ezproxy.macalester.edu/docview/1539634345?accountid=12205
Roper, E., & Brandt, S. (2014, Sep 01). West river parkway in minneapolis to remain closed until 2015. TCA Regional News Retrieved from http://ezproxy.macalester.edu/login?url=https://search-proquest-com.ezproxy.macalester.edu/docview/1558548008?accountid=12205
Williams, B. (2016, August 31). Minneapolis' West River Parkway reopening after mudslide. Retrieved from https://www.mprnews.org/story/2016/08/31/minneapolis-west-river-parkway-reopening-after-mudslide
Nice blog, Marissa! I am currious about the kind of soil they used when reconstructing the slope. Did they opt for a different kind of better draining soil? I also wonder about the plans for continuing to use that area as a path. Could all the use and pressure cause another failure despite all the monitoring?
ReplyDeleteI have seen some signs of little slope failures in Saint Paul along the Mississippi River - sidewalks cracking and sloping down, trees being pulled down the slope, rockfall. Could an event like this one happen in Saint Paul? I hope not!
Thanks, Betsy! They did use a soil that would drain better. They also put in some new vegetation to increase the integrity of the slope. Because of all the new implemented devices, I doubt that a similar rainfall would cause the same reaction in this particular area (as it was mostly related to water not draining), but I am sure that other areas along that road are at risk. We don't tend to preemptively replace soil and retaining walls. We will keep our eyes on Saint Paul and cross our fingers! The atlas will hopefully help with that!
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