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Teri Higgins June 30, 2016 Page 11 2.Existing Sewers a.Sewers in Non‐Liquefiable Areas. Pipe joints may crack due to shaking. Pipeline collapse will be limited. Continue to slip‐line sewers if required for other reasons. It will reduce the potential for cracking and infiltration following an earthquake. b.Sewers in Low Probability Liquefiable Areas (0 – 5% probability and PGDs of 4‐inches or less). These areas are found along the Willamette River. If liquefaction occurs, there will be some pipeline damage, although the probability is small. For critical (large diameter pipes 24‐inches and larger) pipelines that are difficult to access for repair (e.g. river crossings), consider slip lining them to hold the pipe segments together. Products such as those available from Insituform (polyester liner) should be adequate, although the lining material has limited ductility. HDPE slip lining would be preferred as it is much more ductile. c.Sewers in Moderate Probability Liquefiable Areas (5 ‐ 15% probability and PGDs greater than 4 inches. These same areas are subject to landslides with a 15 – 30% probability of occurrence and with PGDs potentially exceeding 100 inches. These areas are found in the hills in southern Eugene. These pipelines are typically 12‐inches diameter or less serving small areas. It is difficult to mitigate these sewers if large PGDs occur. Slip lining the system with HDPE would have the greatest likelihood of success, but even that may be limited. Make sure that damaged sewers can overflow to the River without backing up buildings or overflowing into the streets. 3.New Sewers a.Sewers in Non‐liquefiable areas. Use pipe with joints that can accommodate small differential movements (less than ½”) without cracking. Standard bell and spigot pipe with rubber gaskets is acceptable. Pipe materials can include concrete, vitrified clay, and PVC. b.Critical Sewers (24‐inch and larger) in Low Probability Liquefiable Areas (0 – 5% probability and PGDs of 4‐inches or less). These areas are found along the Willamette River. Design the pipe to be neutrally buoyant so if the surrounding soil liquefies, it won’t float. Use specially designed pipe with double depth bells to limit joint pull‐out of segmented pipe. HDPE, reinforced concrete, steel, or ductile iron pipe is required. For difficult to access locations (e.g. river crossings) use continuous or restrained joint pipe such as HDPE, steel with welded joints, or ductile iron with restrained joints. c.Non‐Critical Sewers (less than 24‐inch diameter) ‐ Low Probability Liquefiable Areas (0 – 5% probability and PGDs of 4‐inches or less). These areas are found along the Willamette River. It is preferred but not required to design the pipe to be neutrally 2020 Eugene Wastewater Master Plan Appendix A-11