CSAH 42/Mississippi River landslide repair
In the spring of 2003, a landslide occurred on CSAH 42 between Rogers and Elk River as a result of high Mississippi River waters pounding into a section of a very steep 50-foot-high slope. Smaller slides had occurred over the past few years in this area. Stephan Gale of Gale-Tec Engineering, Inc., and Wayne Fingalson of Wright County described how they used a fast-track approach to repair the roadway in roughly two months.
The landslide extended into the northbound lane and came close to affecting the southbound lane. A temporary holding system of helical screw anchors, geotextile, and chain-link fence prevented loss of additional ground during the two months it took to evaluate and design the repair.
Repair systems that were analyzed included gabion walls, soil nails, lightweight fill, and mechanically stabilized earth systems. The distance between the river and the top of the slope allowed for either a retaining wall or the creation of a very steep manmade slope of one horizontal to one vertical.
The most cost-effective design, and that chosen for the repair, included a combination of a high-tenacity polyester geogrid-reinforced earth system with riprap facing and sheet-pile for flow diversion in the flood zone, and a cellular confinement system facing with a special fertilizer/seed mix in the upper portion of the slope.
A seed mix consisting of deep-rooted prairie perennial grasses was specified along with a special organic plant food/fertilizer with a slow-release nitrogen that is an excellent grass starter with low burn potential. This natural fertilizer is compost-based and heated in processing, which stimulates the micro-organism growth.
Regulatory agencies including the Division of Waters and the Division of Fish and Wildlife of the Minnesota Department of Natural Resources; the Soil and Water Conservation Service; the Corps of Engineers; and the Mn/DOT State Aid Disaster Committee were contacted for necessary permits or approvals. State Aid disaster funding paid 100 percent of the costs, and the project stayed on budget, said Fingalson.
Due to its considerable experience in this area, Gale-Tec Engineering, Inc., was retained on June 26, 2003. The design was completed on August 22. Contractor Veit & Company was awarded the work on September 9, traffic diversion began on September 10, and 750 lineal feet of riprap was completed by October 7. The project was substantially completed by October 31, 2003. To allow for settlement to take place, final pavement wear surface and curb was placed in April 2004.
For more about the project, contact Gale at smg@gale-tec.com or Fingalson at wayne.fingalson@co.wright.mn.us.
Source material adapted with permission from Stephan Gale and Wayne Fingalson.