Seattle imposes a local requirement for verification testing of shoring tiebacks in addition to proof and performance testing. Because the required test load is 2.0 times the design load, and our design safety factor is 1.5, the test is almost certain to fail the anchor on the soil/grout interface. At least, if our design achieves the target conservatism, the verification test ought to fail the soil/bond interface; otherwise our strength estimate is low and our design is pointlessly conservative.
One charming aspect of such high test loads is that verification anchors need additional strands in order to safely transfer the test load down to the bond zone. (We prefer to test a typical bond length with extra strands rather than use a typical strand count and shorten the bond length.) that means that the test anchors look really robust. The anchor below is only a 180-kip anchor, but it has 9 strands because it’s going to be tested to 360 kips.
Another fun aspect of testing sacrificial anchors is that they need to be installed in between soldier piles so they don’t take up the pocket for a production anchor. That means that we get to use a cool reaction frame for the test. Setting the frame is an extra step, but I think it makes the test setup look super old-school.
Really, though, the point of this post is just to share the photo that Wes sent down from the jobsite. The test results, to be honest, were disappointing. The setup is really clean and efficient, though. We’ve already installed a similar anchor and then post-grouted it looking for higher capacity. I expect that later today we’ll have a similar photo of a great looking verification test and also proof of the high strength we used in our design.