[EarthResearcher333]

28 Anchor Tendon Cracks in 8 Radial Gates "Considered Significant" - 2 Anchor Tendon Failures - DWR moving goalposts? on crack size criticality definition?

From test report data, all of the Anchor Tendons in the Radial Gate structure should be replaced in the new repairs. Why? The structural integrity to sustain the forces for the "repair capacity" of 271,000 cfs flow requires "known good" anchor tendons.

= = = Apologies in advance as this is a long post. However, this information is required to demonstrate a very confusing & conflicting history of engineering statements vs data on the Spillway Radial Gate Anchor Tendons.

Below is a confusing history of disturbing engineering integrity issues (human & engineering data) on Oroville's Radial Gate Anchor Tendons. From meandering on inferring "no defects found", to what "defects" considered significant, then redefining "defects" as "minor flaws", ignoring real flaws, then creeping to a known "critical failure crack size".

In 1999 ultrasonic testing was performed to test for "cracks" in the anchor tendons [1]. As 2 prior tendons had failed from corrosion induced cracking, failure analysis data determined that 1/8 inch is the actual critical crack failure depth [5]. In the final March 23, 2000 analysis report, performed for DWR, it was stated that 1/32 inch or greater was "considered significant" in a crack depth [2]. The report identified 28 anchor tendons that had 1/32 inch or greater cracks [3][4]. All 8 Radial Gates had anchor tendons with 1/32 inch or greater cracks. See below [3][4].

Amazingly, in 1999 a letter from DWR to FERC, stated that testing and detailed analysis of the Radial Gate Tendons were completed in Sept 1999 and "no significant defects were noted" [1]. The letter went on to ask FERC for an extension for time, to March 31, 2000, for the full report due to a heavy workload and reduced staff [1]. When the report was completed March 23, 2000, the report found 28 tendons that had defects that were "considered significant" [2][3][4]. So how can DWR state to FERC that "no significant defects were noted" [1] when the subsequent report HAD significant defects in 28 tendons in all 8 Radial Gates? [2][3][4]

Then, in 2012, a letter response by FERC from DWR's initial submittal, DWR's initial letter had stated that 1/16 inch cracks and below were considered "only minor flaws" [6]. What happened to 1/32 inch as "considered significant"? [2] Worse, the March 23, 2000 report identified 12 tendons that had cracks that were OVER 1/16 inch.[3][4] What happened to these 12 tendons? I've been unable to find FERC filed documentation on repair replacements to these 12 tendons (affecting Gates 1, 3, 4, 5, 6) [3][4]. Actual failure data noted that at 1/8 inch is where the tendon completely fails [5]. So there are 12 tendons that are ignored as more than 1/16 inch (minor flaw) and some just under 1/8 inch (complete failure). What happened to the 1/32 inch as "considered significant"?

I recognize that new discoveries of metallurgical structure failure information may revise these risk dimensions, but where is the supporting FERC/DWR communications & documentation? The only pattern is (A) a case of a direct false statement of "no significant defects were noted" [1] (Sep 1999) when the subsequent follow-up 2000 finalized report found 28 "significant" cracks[2]. (B) The numbers keep changing upward AND the usage/meaning of the wording decreases - is this misleading intentional? (going from "significant" at 1/32", to "minor flaw" at 1/16"). ( C) 12 tendons disappeared off of the radar as these were above 1/16" and some close to the actual known failure of 1/8". Why?

Now, in the midst of the Spillway crisis, do we have a potential repeat of (A)?. -> In the Sept 2016 Dam Safety Inspection report it noted that all 384 tendons were tested with a new experimental method of Dispersive Wave Testing. This report noted that test data will be available in March 2017. In a Feb 1, 2017 letter, DWR stated to FERC that no irregularities were found in this dispersal wave technique anchor tendon testing, however they needed more time for analysis [7]. (Is this going to be a repeat of the 1999 episode of stating "no significant defects were noted" with the actual final report "finding significant defects"?) The same DWR letter to FERC asks for a delay extension to Sep 1, 2017 for the final analysis "study" to compare to an actual test rod in the lab (not the fault of DWR but of a glitch in reproducing a metallurgically accurate test rod). Will these final test results come back with data that contradicts the earlier DWR to FERC letter saying "everything is ok" meme?

Given the history pattern of all of the above, there is a perceived issue in loose engineering standards, and in some cases, outright self conflicting information. What happens to "trust" in integrity with this demonstrated history?

[1] In 1999, DWR letter to FERC stated that testing and detailed analysis of the Radial Gate Tendons were completed in Sept 1999 and "no significant defects were noted".

[2] 2000 report (from 1999 testing and initial detailed analysis) finds 1/32 inch cracks "considered significant" in 28 anchor tendons affecting all 8 spillway gates. This directly conflicts with DWR's letter to FERC in 1999 [1] above.

[3] 2000 report listing the "significant" crack identified anchor tendons - page 1 of 2. Some of these cracks are over twice the size of 1/32 inch being over 1/16 inch.

[4] 2000 report listing the "significant" crack identified anchor tendons - page 2 of 2. Some of these cracks are over twice the size of 1/32 inch being over 1/16 inch.

[5] 2000 report - Failure analysis determines that tendon failure occurs at 1/8 inch and is considered "critical failure crack size"

[6] 2012 DWR/FERC communications where DWR's initial submittal now redefines 1/16 inch as "minor flaw". What happened to 1/32 inch "considered significant"?

[7] 2017 DWR to FERC noting "no irregularities revealed" in new Dispersive Wave Testing, but the final analysis & lab test results will be delayed to Sep 2017. Will this final report conflict with the "no irregularities revealed"?

[abb]

April 25, 2017 7:29 PM
What went wrong at Oroville Dam? Analysis points to drainage, problematic soils

By Dale Kasler
dkasler@sacbee.com

The spillway failure at Oroville Dam likely was caused by problems with its underlying drainage system and the soils beneath the concrete chute, according to an internal analysis by the U.S. Army Corps of Engineers.

The April 7 report marks the first time the Army Corps, which sets rules governing reservoir operations, has attempted to pinpoint the causes behind the Oroville spillway crisis, which led to the two-day evacuation of 188,000 residents in February.

The Army Corps’ report, conducted by its risk management center, generally dovetails with other analyses about what caused the spillway to split in two Feb. 7. The presence of compacted clay instead of solid rock beneath portions of the concrete chute helped undermine the structure. The underlying drainage system didn’t function properly and the steel bars anchoring the spillway to the rock were too short, the Army Corps group concluded.
ADVERTISING

“The underdrain system, poor geologic conditions with compacted clay leveling fill, and marginal design details likely led to the incident,” the Army Corps group wrote in a 14-page memo to Eric Halpin, the agency’s deputy safety officer. The Sacramento Bee obtained a copy of the report Tuesday.

Read more here: http://www.sacbee.com/news/state/california/water-and-drought/article146789099.html#storylink=cpy

[mad_as_he$$]

WoW! Just WoW!. The denial is strong in these folks.

Folsom - just down the road from Oroville:

The hydraulic load on this type of spillway gate (Tainter gate) is transmitted from the cylindrical skin plate, which is in contact with the reservoir, through a number of struts to a convergence at the trunnion hub. The hub collects the load from the struts and transfers it across an interface to the trunnion pin, which is stationary and is connected to the dam. When the gate is operated, the hub rotates around the pin. The struts are primarily compression members, but friction at the pin-hub interface induces a bending stress during gate operation. Typically, and in this case, the struts are oriented such that the trunnion friction stress is applied to the weak axis of the struts (see Section modulus). In order to better handle these loads, the struts are connected with diagonal braces that take the stress as axial loads. At Folsom Dam, increasing corrosion at the pin-hub interface had raised the coefficient of friction and, therefore, the bending stress in the strut and the axial force in the brace. The capacity of the brace connection was exceeded and it failed. This caused the load to redistribute and the failure progressed, eventually buckling the struts.

[EarthResearcher333]

Big Picture of Oroville's Large Radial Gates, Anchor Tendons, Trunnion Anchor Block, Chute Columns, Struts, Diagonal strut braces

This illustrated image provides visual details to the technical terminology names of Oroville's rotating Radial Gates. Lift motors, with cables, on the upper "hoist deck" will lift these massive radial gates to allow water to flow in the Gate Chute openings. The radial gates have inflatable seals along there sides that are hydraulically pressurized to enable a controllable watertight seal. The bottom of the Radial Gate has a compression rubber type of seal that operates by the sheer weight of the Gate compressing it along the bottom edge. Stainless steel "slide plates" are used on the boundary of the radial gate edges, bonded to the concrete column face, to provide a smooth surface for the side seals.