I was in the middle of a long, boring car drive recently and started daydreaming how nice a comprehensive high-speed rail network in the USA would be. That dredged up a memory of testing in northern Italy, nearly 20 years ago…
The Milan–Bologna high-speed railway link is part of the Italian HSR network. It runs parallel to the historical north-south railway between Milan and Bologna, which itself follows the ancient Roman Road, the Via Aemilia. Back in the early 2000’s, I was onsite to conduct bi-directional testing for the new bridge being constructed over the Po River for this rail line.
A previous phase of the project included preliminary testing of dedicated test shafts. Now, the construction phase was well underway, and a production test had to be carried out.
Since it was offshore, the test shaft naturally was permanently cased. The top of the test shaft casing along with all the other shafts in the pier was utilized as structural support for the template and work platform. This presented a problem: By definition, any load test on a single shaft presumes it is isolated and free to displace independently. This one was an integral part of the work platform, and there was no way to cut it loose (I checked).
This signature project was now in a real jam. The contract documents required the test, all the testing equipment was already installed in concrete but the test was essentially impossible to carry out correctly. Furthermore, if the temporary works design engineer had not considered the need for having the test shaft remain isolated when designing the template and work platform, he most certainly did not contemplate the load condition of a single foundation element actively pushing upward into the template. The test could potentially compromise the work platform structure itself. There was no way forward, and no way back.
After some intense discussion (and, I imagine, some very colorful Italian), it was decided to proceed with the test, but carefully, prego? The testing team added some spot-weldable vibrating wire strain gages to the outside of the casing above the waterline to estimate the amount of load transferred to the template (which became in effect a reaction frame). Later, during the analysis of the test data, I deducted the reaction load from the shaft capacity.
Once everything was set, we proceeded oh so cautiously with the test. You might even say we tried to sneak up on each load increment. Luckily, overall displacements were minimal, although there was some creaking and the deck of the work platform did heave visibly toward the end of the test. The reported results had to include all sorts of caveats regarding additional assumptions that had to be made about the measured data. In the end, the test was a headache for everyone but a success.
The reason I’m sharing this story is to illustrate that while creative site engineering can get you out of a jam, proper planning is always the better way to go. It doesn’t matter if you are a design engineer, general contractor or drilling subcontractor. If you are looking at any type of deep foundation system load testing, talk to us. The earlier in the project cycle the better. LTC can help formulate a successful test plan and help avoid pitfalls that could derail your project (sorry, couldn’t resist). LTC’s founders and principals have load testing experience spanning the world and going back over 20 years. We haven’t seen it all but we have seen most of it.
LTC