The 2 failed Oroville spillway tendons have been replaced. However I have not been able to find bid instructions for these two tendon repairs. I have found DWR bid repair instruction documents for the replacement of tendons in the Clifton Court Forebay Dam. See below.
There are significant construction differences between Oroville and Clifton Court Forebay Dam tendons. Oroville's anchor tendons are encased within a steel sleeve, with grout emplaced between. Whereas Clifton Court's tendons are not encased within a sleeve. Oroville's tendons are tightly spaced with an array of two rows of 12 (total 24) tendons per trunnion side in a tight grouping. Clifton's tendons are just two larger tendons per trunnion side (easier access). Oroville's tendons are post-stressed while Clifton's are pre-stressed.
Replacing the Clifton tendons are easier (see below) verses Oroville's. We had upthread discussion on how Oroville tendons likely would be done. The challenges would be in (1) coring either inside of the sleeve to drill out the tendon & grout. or (2) coring out the whole sleeve & tendon (larger diameter core hole). If (2), then there is the necessity emplacing of two layers of re-grouting of outside the new sleeve and inside the sleeve. If you have 2 layers, you have 2 curing times as the sleeve will act as a binding seal on the post-tensioned anchor. The other challenge is the "Tee" anchor (7 inches by 2 inches approx). It likely needs to be removed from the side of the Chute Column as a "coring" diameter that encompasses a "Tee" may be too large for the tightly spaced grouped array of tendons. If the tendon to be replaced is in an inner "Tee" location, then the neighboring Tee anchor will likely be in the way from the side access. This too must be fixed & replaced (possibly another whole tendon assembly) if "cut through" to get to the inner tendon anchor.
Reversing the process: The new tendon "Tee" anchor must be grouted in first - then wait for curing to load strength - then the tendon is tensioned to the specified tensile load (near 160,000 psi), (somewhere in the process grout is emplaced in the sleeve - the grout will then cure to strength).
= = Clifton Court Forebay Dam Bid on replacing anchor tendons:
2. Install new anchor tendons for Radial Gates 1, 3, and 5 on the Clifton Court Forebay control structure. This work includes the following principal features:
a. Modify existing concrete control structure piers and abutments.
b. Core new holes, install, grout and tension new anchor tendons.
c. Fabricate and install new bearing plates.
DWR bid instructions on Tendon Replacement - Clifton Court Forebay Dam
To EarthResearcher333:
Thanks again for the post cross referencing your radial gate anchor tendon diagrams and putting them together in one place. These really help in gaining a better understanding the scope and scale of the issues; but do generate fodder for further questions! I’m still way down on the learning curve, but trying to catch up.
Replacing the gate anchor tendons appears to be quite a significant endeavor, as you’ve been pointing out for a while now. Besides the problems you identified in accessing the internal “Tees” from the side of the columns, and spreading the grout out enough to eliminate air voids on both sides of the sleeve, I would think there might also be difficulties with the coring out of these 37’ long tendons in the first place. The bit would have to drill through a composite of steel, grout, concrete, and rust for 37’ consistently without clogging enough to bind or break. If the grout and rust hold the tendon in tension, the compressive force reaction would substantially increase the bit’s tendency to bind. A broken or non-recoverable bit could result in a tendon that couldn’t be replaced, so there would be little room for error across the thousands of feet of coring required.
Is it a common practice to core out and replace tendons this long? How long does this take per tendon? Does the hole size increase significantly? Do you have pictures showing how this is actually done for tendons of this size?
Are there other plausible alternates for restoring the full original design safety-factor gate tension? Assuming they could find the room, could they drill new holes and grout in additional new tendons to compensate for the strength loss from the existing corroded tendons? This might strengthen the gates sufficiently until proper diagnostics could determine which of the hundreds of tendons actually need replacing, as that may not be until later this year, on DWR’s schedule. I would think DWR would need a “Plan B”, if they don’t have time to replace the tendons this year, which seems likely.