More Reading:[1] California State Assembly Hearing with DWR alerts residents to the hazard of problems with the Oroville Dam - May 14, 2017 - @liatrissaga/california-state-assembly-hearing-with-dwr-alerts-residents-to-the-hazard-of-problems-with-the-oroville-dam[2] DSOD Feb 3, 2015 Inspection report - Picture 8 - "Red telltale paint, left, marks the extent of a crack in the Gate 8 pier. The recently refreshed paint shows that the crack now extends below the dashed arrow to the concrete chamfer. Monitoring should continue."[3] DWR Ultrasonic testing report 2000 - 28 anchor tendons with greater than 1/32 inch "reflector" flaws "considered significant" affecting all 8 Oroville gates - 12 greater than 1/16 inch, 1 very close to 1/8 inch "critical failure size" - -backup.ferc.gov/IDMWS/search/advResults.asp 20000419-0130(977645).tifFailed Tendons - page 3, 4 - inferring 100% coverage by crack location of sample of 2 failed rods. Annular space between rods and protective pipes not properly grouted - Page 4. Water entered annular space through open grout ports - Page 4. It is "believed" that the rods were exposed to a corrosive environment over time as moisture accumulated within the unexpected voids. Page 4. The critical crack size in the case one of the Oroville rod appeared to be about 1/8 inch. - Page 4[4] Trunnion Rod Microcrack Detection - US Army Corps of Engineers - -bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA583523 file: ADA583523.pdf"Post-tension rod loss occurs as an orthogonal brittle failure when a propagating cross-axial microcrack reaches a critical threshold. For ungrouted rods, this has resulted in rods being ejected under extreme velocities. Heavy retrofit cover box housings have been constructed to help contain failing rods. It is not known if the defect growth and resulting rod failure rate will stay at its relatively low number of a handful per year across the Corps inventory or whether it will increase as older rods continue to be in-service and defects continue to slowly propagate until reaching a threshold total failure point."[5] 28 Flawed/cracked tendons & reflector dimension Page 14, Page 15 (Oroville dam) Page 15 (Pyramid dam 1 gate) -backup.ferc.gov/IDMWS/search/advResults.asp 20000419-0130(977645).tif[6] Calculation in estimating flaw equivalent crack size - Page 20, Page 21 -crack "reflector" representative of a corrosive type circumferential loss of material, the area calculation is a good comparative tool for evaluating possible reductions in load bearing area & estimate to crack induced failure. - -backup.ferc.gov/IDMWS/search/advResults.asp 20000419-0130(977645).tif[7] Ultrasonic testing - 1/32 inch "reflector" at 10 inches can be detected - Page 4 -backup.ferc.gov/IDMWS/search/advResults.asp 20000419-0130(977645).tifLimited to 3 to 4 feet in entire 40 foot rod length - Page 4 1/32 inch at 10 inches can be detected - Page 4 (thus limited to 1/32 inch crack in 10 inches - infers that 97.9% of 40 foot rod not identifiable past 10 inches).[8] Clifton Court Forebay Dam (DWR) Failed tendons causing Failure of Radial Tainter Gate 2 - corrosion induced - grout problem from original construction - 100% of anchor tendons replaced in 4 out of 5 gates since emergency failure of the Spillway. _Clifton%20Court%20Forebay%20Dam.pdf"incomplete grout coverage surrounding all these tendons near the anchor head" "Other information obtained from the results of NDT indicate loss of performance and potential deterioration of the original tendons installed during construction of the forebay. This includes relatively low remaining prestress in two of the tendons supporting Gate 3, and incomplete grout coverage surrounding all these tendons near the anchor head. Results from electrochemical testing indicate electrical connectivity between some tendons, as well as potential differences with nearby tendons that may have facilitated corrosion of tendons prior to the failure of Gate 2."[9] SUMMARY OF BIDS RECEIVED FOR EMERGENCY RADIAL GATE REPAIRS CLIFTON COURT FOREBAY DAM - July 24, 2013 - Contract awarded July 25, 2013, Cal Neva Construction Services, Inc.- -15_Summary.pdf[10] DWR & LLNR low frequency full depth test project - to measure full length of anchor rods - was unsuccessful - -backup.ferc.gov/IDMWS/search/advResults.asp 19990322-0490(533695).tif March 3, 1999. DWR to FERC letter "Oroville Dam Radial Gates' Trunnion Anchor Rods Inspection."Our original program, which included full depth testing of the trunnion anchor rods by Lawrence Livermore National Laboratories, was unsuccessful. Accordingly, the Department of Water Resources will inspect the upper 4 feet of each of the 382 anchor rods, using conventional ultrasonic testing equipment and inspection methods" [11] "The report documenting the results of the testing and detailed analysis will be submitted to your office by December 31, 1999." [12] "conventional testing equipment is only effective at detecting flaws in materials up to approximately 4 feet in thickness or length. LLNL's research program was to develop a field testing method that could detect any flaws in the post-tensioned rods to full depth."[13] FERC to DWR Re: Oroville Dam - Testing of Radial Gate Trunnion Anchor Tendons - August 1, 2012 - "This is to acknowledge receipt of the Department of Water Resources' (DWR) letter dated June 27, 2012 that transmitted the Oroville spillway gate trunnion anchor tendons testing report, part of the Feather River Project No. 2100. Given that the results of the ultrasonic testing are still under evaluation, DWR's request for a time extension to submit the final test report by August 31, 2012 is accepted." "We appreciate DWR's continued cooperation in this aspect of the Commission's dam safety program." -backup.ferc.gov/IDMWS/search/advResults.asp 20120810-0330(27481892).tif[14] FERC/DWR communications Oct 31, 2012 "We received the Department of Water Resources' (DWR) August 27, 2012 letter that transmitted the Oroville spillway gate trunnion anchor tendons final testing report." "We note that only minor flaws, i.e., 1/16 inch or smaller were discovered in the testing investigation." "DWR's plan to perform regular annual testing starting in 2013 is acceptable. Results of the annual testing should be included in the annual Dam Safety Surveillance Monitoring Report (DSSMR)."(infers no testing from 2000 to 2011) [15] DWR to FERC communications: December 27, 2013 -backup.ferc.gov/IDMWS/search/advResults.asp 20131227-5142(29015672).pdf"By letter dated September 24, 2013, the Department of Water Resources (DWR) requested a time extension to address comments provided by the Federal Energy Regulatory Commission (FERC) on the 2011 Structural Re-Evaluation Reports of the radial gates for Oroville, Thermalito Diversion, Thermalito Forebay, and Thermalito Afterbay dams. Subsequent to DWR's request, engineers from DWR and FERC held a productive conference call on December 3, 2013, during which FERC engineers provided additional guidance. DWR understands that future re-evaluations should focus on failure modes (connections, buckling, trunnion shear, anchorage, etc.) that lead to catastrophic failure of the gate. The consequences of catastrophic failure should guide potential recommendations and any future warranted remedial actions."[16] DWR Board concerned about failures -August 2014 DSOD Inspection report "Observation and Comments" - "The tendon anchors are about 50-years old and could experience problems in the future based on the history of tendon breakage at dams of similar age and construction. The Board expressed concern about this and will make strong recommendations about the need to carefully monitor and test the tendons using the latest tools. Ultrasonic testing of the anchor rods has resumed. At the suggestion of the Board, more informative testing methods are actively being pursued by O&M."[17] FDH-Velocitel DWR to FERC communications - Feb 1, 2017 - Dispersive Wave techniques - -backup.ferc.gov/IDMWS/search/advResults.asp 20170201-5189(31940596).pdf"Although FDH-Velocitel has indicated that field NOE results of the P2100 dams did not reveal any irregularities in the tendons, DWR respectfully requests an extension of September 1, 2017 for the submittal of NOE test results for Oroville, Thermalito Forebay, and Thermalito Afterbay Dams. DWR anticipates a delay in submittal of these test results due to difficulties in procuring 40-foot long steel tendons that match as closely as possible the modulus of elasticity and guaranteed ultimate tensile strength of the in-service tendons. The first steel tendon vendor engaged by FDH-Velocitel manufactured tendons of suspect quality. FDH-Velocitel, DWR engineer's and DWR's metallurgical consultant continue to vet other manufacturers' proposals and samples to ensure the steel tendons procured for prototype testing provide the best match to the in- service tendons. This additional effort will help minimize uncertainty in FDH-Velocitel's testing and analysis." "A contributing factor to the delay includes DWR's desire to submit the entirety of FDH-Velocitel's study that includes field NDE results, modeling, and prototype testing, rather than solely field testing. DWR anticipates submitting comprehensive studies for Oroville, Thermalito Forebay, and Thermalito Afterbay Dams in advance of the requested September 1, 2017 deadline, and a comprehensive study for Pyramid Dam well in advance of the February 1, 2018 deadline.""By letter dated April 8, 2016, the Department of Water Resources (DWR) provided a plan and schedule for the non-destructive examination (NOE) field effort for the radial gate tendons at Oroville Dam, Thermalito Forebay Dam, Thermalito Afterbay Dam, and Pyramid Dam. In 2016, DWR procured the services of FDH-Velocitel to conduct field dispersive wave testing of the tendons as well as finite element modeling and the construction and testing of full-scale prototypes for calibration and validation purposes."[18] Review of Radial Gate Tendon History and Non-Destructive Examination - DWR to FERC - April 8, 2016 - -backup.ferc.gov/IDMWS/search/advResults.asp 20160408-5209(31373879).pdf"By letter dated March 19, 2015, the Department of Water Resources (DWR) submitted a plan and schedule to address Recommendation R-1a from the Ninth Part 12D Safety Inspection Report for Oroville Dam by June 1, 2016. Recommendation R-1 for Oroville Dam consists of: The Board recommends that the following tasks be undertaken to evaluate the potential for failure of the trunnion anchor tendons of the Flood Control Outlet (FCO) radial gates:a) Review performance issues with similar types of tendons on other dams (DWR dams and others). This review would provide useful background to the tasks b and c, below.b) Review previous analyses relating to the sensitivity of the structural capacity of the trunnion supports to the capacity contribution of the anchors. That is, analyses that evaluate how many anchors may be lost before demand/capacity ratios and/or other performance parameters become unacceptable.c) Perform load/corrosion testing using new non-destructive testing (NDT) methods (possibly dispersive wave technology or other methods). Previously used ultrasonic methods have limited depth and flaw detection capability. The testing should be implemented no later than 2017."[19] FEMA dam safety report - Appendix F: The Legal Risks Of A Major Dam Failure - -library-data/20130726-1830-25045-3217/damsafetyreport.pdf"We live in a litigious society. One of the risks of a major dam failure resulting in a loss of life or sub- stantial property damage is litigation. The victims will seek compensation for their losses and the State may bring criminal prosecutions."
Repairing A Catastrophic Failure: The Oroville Dam Update
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