The National Railroad Construction and Maintenance Association (NRC) has awarded GeoStabilization International (GSI)with Small Project of the Year for its work on Union Pacific’s Mankato $2.8-million,90.5 Permanent Landslide Repair project.
When heavy rainfall saturated the soil along the hillside above Union Pacific railroad track near Mankato, Minnesota, the consequences were far greater than simply a landslide. Century-old graves in Minneopa Cemetery were positioned precariously along the failing hillside.
Union Pacific called in GSI and engineering and design firm Olsson Associates for the emergency project. The trio worked together to implement a cost-effective and technically sound solution that successfully mitigated the landslide. Despite challenging conditions at the project site, GSI completed the project on a compressed schedule with zero recordable incidents. NRC award judges found their safety record impressive considering the risks involved in dealing with unpredictable earth movement.
Landslide problems at the project site dated back to 1908 when a series of tiered, stone-block retaining walls were constructed along the slope to stabilize previous hillside failures. Although the walls had been reinforced over the years, excessive precipitation during the winter in 2020 caused the slope to slump and threatened a devastating landslide.
The project team came together quickly but project site conditions created complications: the difficulty of operating in the extreme Minnesota winter weather, the presence of freezing groundwater a the site, and the fact that the slide’s headscarp abutted the graves, which made traditional landslide mitigation methodology impossible.
The first objective was to slow the 570-linearfoot wide slide’s progression. Numerous gravesites were uncovered above the scarp and headstones had to be relocated. Large amounts of groundwater were seeping out of the slide mass, creating supersaturated soil conditions.
After gathering geotechnical date onsite, Olsson personnel directed GSI to install horizontal and trench drains in locations to temporarily stabilize the hillside and to slow the slide’s progression. Once installed, the team began working on the permanent repair.
Given the sheer magnitude of the slide and access difficulties, these solutions would historically take months to design. GSI’s operations and engineering efforts combined with Olsson's geotechnical and site survey expertise to produce a constructible design in weeks rather than months.
Working under the direction of Construction Manager Justin Anderson, PE, and Lead Engineer Dylan Jones, GSI refined the design further during construction based on actual ground conditions discovered during drilling and the results of drone surveys completed after the vegetation was removed. These refinements reduced project costs and created a more constructible design.
The project team implemented a tiered stabilization system consisting of a lower wall – to increase the slope's global stability and protect the railroad from slide debris impacting the tracks' right-of-way – and an upper wall – to restrain the cemetery property line and prevent progressive failures, which could potentially further impact the graveyard at the top of slope.
“For the FRA Part 219 and 243 implementation, the NRC was especially helpful for us in that they provide member companies guidance in how to comply with the ever-changing federal regulations. We also value the annual safety awards which we use to motivate our employees to uphold the highest level of safety as well as in business development materials.”
Ragnar Benson Construction, LLC.