New details & photographs are now coming out on the Oroville Spillway Cracks. These "cracks" are extensive and photos show that some go fully through the thickness of the slabs. (see report and photos)
Perhaps the most significant question, which becomes rhetorical, is "If you knew that it was going to crack as it did, why didn't you use epoxy coated rebar in the lower slab layer?". Simply answering this question is "have you stopped beating your wife" trap. Either DWR knew it was going to crack to the full slab thickness and DWR didn't consider the long term implications of corrosion of the lower rebar - OR - DWR didn't know it was going to crack through the full slab thickness and DWR believed they didn't have to use epoxy coated rebar in the lower layer.
Prof. Robert Bea has been unfairly criticized in other media. Yet the new report buttresses the concerns originally stated by Prof Bea. Massive Oil well structures, constructed of concrete, and within a saltwater environment, requires important specifications to insure a pure intolerance for cracking. These structures also have deal with anchorage stresses for lateral high storm conditions (seas) and including the footing stresses.
Some early youtube shots of the new spillway show water flowing up these cracks to the slab surface. This "water exposure" demonstrates that the slab to base concrete mating surface is resisting in flow routes to the nearest drain(s). Thus "corrosion" of the lower rebar is a given risk from the reported near 200 cracks (plus the unseen ones). This is highly unfortunate. (Rhetorical again ->) IF they were expecting these cracks, they should have used epoxy coated rebar in the lower slab layer as they did in the upper layer rebar (used green epoxy coated rebar in the upper layer).
Of note: Notice the use of uncertain terms in the report (i.e. "theory", "could have", "likely caused"..). These terms wouldn't be used IF DWR fully expected the cracking outcome if you listen to the recent explanations given to the public.
Newly classified CEII report released (with a noted full page or pages "attachment" redaction):
http://www.water.ca.gov/oroville-spillway/pdf/2017/20171102_DWR_TM_SRT-FCO-DOC-09_CEII%20Redacted_Att1.pdf
--- Article (link below) clips: (emphasis mine)
Brown wrote that most of the cracking was likely caused by the vast amount of restraints, including the underlying leveling concrete and slab anchors. That theory was supported by mapping which showed most of the cracks between anchors, he said. Thermal shrinkage could also have been a contributor, though not likely the main reason because the difference in temperature between the top and interior of concrete panels was negligible, according to the report.
Cracking could also have been a result of plastic shrinkage, “usually associated with the rapid loss of moisture caused by a combination of factors that include high air and concrete temperatures, low relative humidity, and high wind velocity at the surface of the concrete.”
In that case, what begins as shallow cracks can turn into deep cracks later, according to the American Concrete Institute, which Brown cited in the report. At the end of the memo, it states that the department would expand its investigation into the cracks and look into modifying the curing process or making changes to the concrete mix, such as using shrinkage-reducing admixtures, which Assistant Professor Feraidon Ataie, director of Chico State University’s concrete industry management program, suggested in a previous interview with this newspaper.
Professor Robert Bea with U.C. Berkeley’s Center for Catastrophic Risk management said on Monday he found two of the pictures, figures one and three in the report which show thin and long breaks in the concrete, significant and “very scary.”
“I hope no one will believe that this type of cracking — not the crazing at the surface of the concrete — is ‘to be expected,’” Bea wrote in an email. “I have helped design, construct, operate, and maintain some very large reinforced concrete structures. These structures had many more ‘restraints’ than the re-constructed spillway. Significant cracking was not tolerated. If found, it was immediately ‘fixed’ and then monitored to be sure that the ‘fix’ had been effective.”
A DWR spokesperson could not be reached for comment before the deadline for this story.
--- end clips more at link
Article: Oroville Dam: Formerly classified memo describing spillway cracks now public
Newly released CEII doc by DWR - shows extent of areas of "cracking" - photo of new slab surface.
Newly released CEII doc by DWR: Full thickness Cracking in new slab - exposure risk to corrosion of unprotected lower rebar layer from upward penetrating water.
