The Bureau of Reclamations dam inventory, like many other agencies, contains inadequately designed spillways that are planned to be completely replaced by new structures or extensively modified to address dam safety deficiencies. This presentation covers two such spillways with inadequately filtered drain systems that led to the development of substantial voids under the spillway slabs. The timeline between identification of voids, risk analysis, corrective action studies, final design and construction can take place over a number of years. Interim risk reduction measures are often used to reduce risks to the public. Available options for interim support may vary given spillway operational constraints and the availability of field staff, materials and contracting difficulties. This presentation focuses on two such cases - emergency use of bicycle tubes to provide confinement for grout backfill of core holes used to measure void size as an emergency footing support at the Dam A spillway wall. In contrast, spillway operations at Dam B allowed additional time after void identification for design and acquisition of helical piles and fabricated brackets to provide more robust structural floor slab support at Dam B.
