RH2 evaluated four reservoirs for structural deficiencies and seismic vulnerability for the Oak Lodge Water District in Oak Grove, Oregon. Two of the reservoirs were 5.0 MG partially buried, prestressed concrete reservoirs built in 1965 and 1988. The other two reservoirs were 2.8 MG welded steel reservoirs built in 1966 and 1989. Construction records were utilized to obtain available structural and geotechnical information, and visual inspections and non-destructive tests were performed to check the dimensions and condition of the structures, foundations, and coatings. Each reservoir was evaluated for conformance with current ASCE 7 lateral loads and AWWA D100 and D110 requirements for welded steel and prestressed reservoirs. The evaluations found that both steel reservoirs require improvements to their anchorage and foundations to eliminate uplift and reduce soil bearing pressures. It was found that both prestressed concrete reservoirs could be brought up to code by constructing interior shear curbs to supplement the existing seismic wall cables. RH2 also evaluated the non-structural and mechanical elements at the reservoir sites and provided recommendations for improvements.
RH2 designed improvements for the two steel reservoirs based on the phase 1 analysis results. The structural design work included foundation expansions and the addition of anchor bolts and chairs at both reservoirs. A new 16-inch inlet was added to the existing single inlet/outlet configuration to improve mixing and turnover in each reservoir. Other additions included a seismic shutoff valve and expansion joints, as well as miscellaneous access and safety improvements.
The steel reservoir improvements were constructed in 2013. Improvements for the two prestressed reservoirs will be constructed in 2014.