The Utilization of Fly Ash for Sediment Stabilization during the Holmes Lake Restoration Project

Often the most difficult issue to address during the planning for the restoration of an urban lake is where to waste the vast amounts of sediment that will be excavated from the lake. In an urban setting, open space is limited and real estate values make it cost prohibitive to purchase land for wasting excavated sediment. Hauling the material to rural areas increases congestion of city streets and can also be cost prohibitive due to the long-haul distance. Furthermore, accidental dumping of sediment along with repeated heavy truckloads can significantly impact the design life of local streets, adding indirect costs to the option of hauling the sediment offsite. As part of the Holmes Lake Restoration Project in Lincoln, Nebraska, 330,000 cubic yards of deposited sediment were excavated across the lake bottom. Due to its urban setting and other site constraints, there were only eight acres of ground available for onsite disposal. The closest offsite location identified for disposal was more than six miles away, potentially adding significant transportation costs to the project. In order to waste the material onsite, the saturated sediment had to be stacked more than thirty-five feet deep. Consequently, the material had to be dried quickly and placed on steep slopes. Several conventional sediment management techniques were investigated for stabilizing the dredged sediment, but all were found to be ineffective. The utilization of a chemical drying agent was the only viable option remaining. It was determined that fly ash incorporation would be the most economical means of stabilizing the sediment from Holmes Lake. The use of fly ash during the Holmes Lake Restoration Project allowed the project to be completed in a timely manner and provided significant cost savings. Type ‘C' fly ash, a byproduct of coal combustion, was found to be effective in drying the wet sediment quickly. Furthermore, the fly ash added strength to the sediment, allowing it to be placed on steep slopes without the possibility of slumping or eroding back into the lake.