Category Archives: Means & Methods

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.

It’s been an interesting week here at Atlas Geotechnical World Headquarters. Our project in Seattle is standing down while Equipment Operators Local 302, who struck last week, continue negotiating a fresh labor agreement with the Associated General Contractors. Three timezones to the left, our project supporting new friends WW Clyde Company in Hanapepe is shut down by Hurricane Lane.

The hurricane, and attendant drenching rains, are on my mind because this afternoon’s task is analyzing hydraulic rise caused by installing bulkhead walls that allow driving access out to the in-water bents. Crane loads during demolition and foundation drilling are legitimately heavy, and the site is crowded, so getting equipment into position has turned into a significant effort.

I include some snapshots from my visit to the site last week. The existing bridge is a graceful reminder of classic Corps of Engineers construction. Built in 1938 for the Territory of Hawaii government, it’s provided reliable service for more than 8 decades.  The replacement bridge will be higher, wider, and safer.  Plus it’ll be free of the weight restriction that is causing difficulties for the re-opened aggregate quarry just a couple of miles up the road.

The temporary bridge is already in place, courtesy of Hawaiian Dredging Company, though the connecting diversion embankments remain for WWC to install.  Our good friend Gary Coover at Pryzm Consulting has the lead on geometric roadway design and utility relocation onto the temporary bridge.  We’ll lend a hand with a very narrow MSE embankment design, but we’ve also got our hands full with crane access designs for demolition and construction.

One last note:  The pipe piles in the photo at right, which support the temporary bridge, were intended to drive 40 or 50 feet into the “compact mud-rock” stated on the 1937 boring logs (I do so love the very effective diction in older plansets). The existing bridge is supported on untreated timber piles 35 to 40 feet long.  Surprisingly, PDA testing during of the pipes showed very low capacity through that known bearing layer.  The pipe pile in the photo is 140 feet long, as long as the planned new bridge shafts. Work in the Islands is just filled with surprises.

Everyone stay safe through the storm, please, and we’ll pick up where we left off once the floodwaters recede.

A brief post this afternoon because it’s been a long day at Hilo Harbor. One of the most common questions people ask me about wharf construction is “how do you get the piles in the correct locations? It’s a good question, because you can’t really use a tape measure from shore, and the surveyor would have to wear water wings to mark the spot. The solution is a lot more work, but is the only way to accurately place the wharf piles in the correct spot: We build a falsework structure and place a template on it. And by measuring really carefully to be sure that the template is in place, we know that every pile that we drive through the template will be in the correct location too.

img_1187This photo has a pretty busy background, which is an unavoidable part of taking action shots of really big equipment in a crowded busy port, but if you look carefully you can see the 999 lowering a 40-ft long template that has positions for driving 20 wharf piles. The surveyor (in a red shirt under his PFD) is walking back to his equipment, which is set up over a very carefully marked spot on the template.  If that spot is in the correct location, then the template is correct. And if the template is correct, then we’re ready to drive piles with confidence. All of the rough-looking steel beans and pipe piles are temporary, and are only there to support the all-important template.

So, tomorrow, if all goes well, we start production piledriving that will continue for the next 6 months