South Bend Township Emergency Levee Repair
This project was located in South Bend Township near Mankato, MN on the Blue Earth River. The contract was for the repair of the west bank of the levee that had collapsed during a weather event in the early fall of 2010. The storm water drainage system experiance a structural failure during a period of high flow. This failure caused seperation of the pipes joints as well as pipe seperations from the manhole structure.
Several thousand cubic yards of impervious levee fill material migrated through these failures and some settled in the pipes, pump station, gatewell and manhole structure. One inlet structure completely diisappeared into the sinkhole. Failure planes and depressions formed in the levee as the impervious fill migrated into the drainage system. All three pumps at a nearby pump station became inoperable and damaged due to pumping of the impervious fill sediment.
Aspen was awarded the contract on 11/10/2010, received the Notice to Proceed on 11/12/2010 and was onsite starting work on 11/15/2010. We encountered extreme weather conditions and were awarded a time extension of 12 days due to the excessively low temperatures and high snowfall. The Mankato area experianced snowfall in the month of December equaling their average yearly amount. Dispite these conditions and the time extension, we were able to complete the work only 2 days past the original completion date.
The work to complete this repair consited of removing all sediment that had been depostited in the system. This was a challenging operation as all work had to be completed under confined space requirements and the sediment encountered was substancially more compacted than anyone expected.
We provided large volume pumps and associated piping as a storm water diversion to ensure the affected neighbor hoods and state highway would not be adversly affected by potential runoff. Luckily with the cold temperatures encountered these did not require operation.
We removed the existing riprap from the riverward side of the leve to allow for excavation at a 3 to 1 slope through the levee. Riprap was stockpiled and reused after completing levee base repair.
We excavated to expose the system piping connections at the manhole structure and found the inlet that had disappeared. Once exposed, we completed a photgraphic and video inspection of both the interior and exterior of the system for 100 feet leading away from the manhole structure.
We replaced 16 feet of 48", 16 feet of 54", 50 feet 30" and 16 feet of 24" reinforced concrete pipe. We repaired the connection of all these pipes at the manhole structure and rebuilt the inlet structure.
Once the underground repairs to the system were complete, we started the rebuilding of the levee section. Impervious clay was placed in 12" lifts, compacted and tested to minimum 95% compaction. New bedding was installed and riprap replaced.
While this work was being accomplished, each pump was removed from the pump house and rebuilt one at a time.
Final site restoration and seeding was completed in late Spring of 2011.
Project Manager: Jon Fank
QC & Safety Manager: Mark Lannon