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Repair of a post-tension design Anchor Tendon involves the removal of the Tendon and it's Anchor deep within the concrete column (usually by a coring of the concrete). When the 2 failed Oroville tendons were replaced, it's unclear if they bored out within the "sleeve" or if they cored out the sleeve in the process (no documentation available). The tough part is the anchor. The size of the anchor "Tee" plate is around 7" in the larger dimension. Thus, the "Tee" anchor + the nut & washer would need to be cored out from the side of the Gate concrete column. To gain access to the side of the Gate concrete column could require the removal of a massive Radial Trunnion Gate - depending on which anchor location in the "arc" needs to be replaced.

I believe DWR fully desires to replace ALL of the anchor tendons in the new upgrade to the spillway. Why? Why fix the main spillway with flowing monies available and then have another crisis from 50-year-old dying Anchor Tendons blowing out? However, replacing these Anchor Tendons requires (1) removal of the Radial Gates. Removal of the Radial Gates poses a safety problem if the reservoir rises. (2) They would have to build a coffer dam to protect against not having the Radial Gates installed. (3) a coffer dam poses a safety risk if not properly built and sealed (piping issues). (4) Head pressure to the coffer dam requires a sizable structure if primarily using gravity mass. (5) The Inlet geometry design of the Flood Control gates needs to be restored if laminar flow (non turbulent flow) is to be insured to original design conditions.

Because of (1)(2)(3)(4)(5), I believe they may build a new RCC based inlet structure that facilitates a temporary RCC coffer dam. When the temporary RCC coffer dam is removed, the RCC inlet structure will remain. This inlet structure would help with regard to controlling piping issues as the current inlet design is erodible. Having an RCC inlet structure (when done) also gives the added benefit of being able to drain the reservoir via the Main Spillway Gates to a lower elevation without the "scouring erosion" problem they have to avoid with the current erodible inlet. (I believe they are limited to a 22 ft margin 835ft reservoir to 813.6ft gate inlet floor).

This raises the question if they are able to work on the ES & MS simultaneously. Using the existing modified Emergency Spillway would have to be a backup in case the repair work on the Main Spillway is not ready in time for an unexpected filling -or- and unexpected failure of the Hyatt power plant.

They should tell the public if this is their plan - Many people would want to know that the Emergency Spillway would become a primary contingency in this case.

Oroville Spillway Anchor Tendon Blueprint - notice the density of the array of Tendons. Anchored endpoints, of the 24 tendons & their anchors in the concrete, are spaced radially in a "fan arc" shape.

More Discussion: Looking at the Radial Gate Outlet Blueprints, it's possible that all of the Anchors to the tendons are accessible for "side coring" removal & new tendon installation repair if the Radial Trunnion Gate is fully raised.

This would greatly simplify the project as only "stop logs" would be needed to dewater the entrance to the spillway gate. (No coffer dam).

I suspect they would have to sequence the timing of tendon removal & replacement as some "alignment support" is required to keep the trunnion pin secure (via the trunnion anchor beam). Before the new Anchor Tendons may be post-tensioned to tensile loads, the anchor concrete must reach curing to "design strength". Any staggering of the "curing to design strength" timing could widen a completion window.

Then there is the "parallel factor". To do all of the anchor tendons in an optimized window of time requires teams of workers working in parallel on all of the gates simultaneously. Big bucks in equipment & expertise all at the same time...... A challenge in Logistics.