1994-03-10_REVISION - M1977378 - Laserfiche WebLink

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TR-14 , File No. M-77-378 Page 2 The remaining proposed steel area addition will be for the purpose of assuring that any failure mode from overstress conditions (which is improbable because of design loading assumptions) cannot be a brittle failure (ie sudden) . The bulkhead length required (ie 3 feet) did not change because in the original design 3 feet was a selected minimum length and was reinforced accordingly. This is also the case in the proposed design. 2) Add a 6 inch diameter pipe to the Terry Tunnel bulkhead design. The approved bulkhead design for the Terry Tunnel does not include a drainage or bypass pipe. It was felt that with the anticipated timing of construction, the American Tunnel water treatment plant would never have to treat the peak Terry Tunnel flow along with the normal American Tunnel flow (although the American Tunnel bypass pipe was designed for the combined flow) . It now appears feasible that this event could happen either through the construction time-line or other circumstances. While the American Tunnel water treatment system may be able to treat the combined maximum flows to CDPS discharge limits, it is more prudent to construct for the possibility that both treatment systems will be required and minimize the chance of discharging water that does not meet CDPS limits. To provide the above discussed flexibility, SGC proposes the following changes to the bulkhead design and other related commi tment s. a) A 6 inch diameter , Schedule 80, Grade 316L, stainless steel pipe will be placed through the Terry Tunnel bulkhead . The pipe will be fitted with a 3/8 inch thick , Grade 316L thrust/seep collar that is 4 inches larger in diameter than the pipe. This thrust collar is designed to resist thrust on a closed pipe by the maximum design pressure. It will be placed a minimum of 5. 5 feet from the downstream face to allow shear and thrust forces to be distributed. The design by John Abel is attached. Schedule 40 pipe is specified but Schedule 80 is being proposed for increased durability in the event that the valve is not closed for an extended time period. b) The rebar cage will be modified to accept the pipe similar to the American Tunnel rebar cage. #6 rebar will be used to provide reinforcement for the pipe opening (similar to the American Tunnel rebar cage) with each bar extending across at least 2 cage horizontal bars. There will be 3 . 5 inches clear distance between pipe and reinforcement.