Temporary Solution Makes Milling in Two Passes Necessary
At an altitude of 235 m, the earthfill embankment dam on Lake Oroville dams the waters of the Feather River. After several weeks of rainfall, the dam reached its maximum water level of around 4.3 billion m³ in the winter after only 50 days. As a result, the owner, the California Department of Water Resources, had to initiate flood control measures at an early stage. The water was discharged in a controlled manner over the top of the dam structure at the level of the dam crown and the adjacent spillway. Due to the large quantities of water and the extremely high water pressure, however, the 55 m wide, main concrete spillway eroded to such an extent that rehabilitation was unavoidable. The damage was initially minimized provisionally by filling the erosion in the surface with rolled concrete, “so that the owner could open the overflow system during the winter months, if necessary,” explains Chris Anderson, project manager at the subcontractor, milling service provider Anrak. This temporary material had to be removed prior to final concrete paving with Portland cement, however, in order to achieve the desired surface quality. To complete this task, the contractor decided to use two cold milling machines from Wirtgen.