Copyright © 2011-22 Helical Pile World, LLC. All Rights Reserved.
Helical Load Tests:
The Low-Down on the Load Test
Recently, Danbro provided some on-site assistance with a load test for an expansion of a municipal building in New Jersey. As most readers are aware, a pile load test is a procedure to test the estimated designed pile capacity by applying a load (compression, tension, and/or lateral) on the helical pile. This was a compression test, required by the owner’s consulting engineer, to determine the viability of a given helical pile to achieve capacity at a certain depth. The geotechnical report indicated loose sands to 20’; dense sand between 20’ to 30’; loose sand to 40’; and very dense sand below that. Based on the experience of the GC, who built the original structure, and consultation with the helical pile installation team, it was decided to test the pile in the upper dense layer in lieu of the recommended pile termination in the lower very dense strata.
If the sacrificial test does not meet the design requirements, the installing contractor must modify the helical pile design and/or installation methods and retest. These modifications may include: de-rating the helical pile load capacity; modifying the installation methods and equipment; increasing the minimum effective installation torque; changing the helix configuration; or changing the helical pile material. In this case, the plan was to test a 2 7/8” pipe pile with a 10” 12” 14” configuration and alternatively a 10” 12” 14” 14” to determine if one outperformed the other. It is not uncommon to use load tests to pick the best performing pile as was the case for a five-story apartment building in Philadelphia. The right pile can eliminate a variety of potential site complications, saving time and money, making the load test well worth the effort. Click to see Ridge Avenue
Danbro has also successfully conducted load tests to prove that an alternative, less expensive, pile can achieve capacities equal to or greater than required, thereby winning jobs for our installers by reducing the cost originally budgeted for the foundation. Load tests should not be viewed negatively as another hoop the installer needs to jump through. They can be used to your advantage to compete on a project as was the case on this project in Boston. Click to see Newbury Street
Many helical piles and anchors that go in the ground are never load tested. With good soil information, pile design input, and experience, pile performance can be accurately estimated. However, Danbro has conducted, assisted, or advised owners or our installers on many compression, lateral, or tension tests. As was the case on the above-referenced projects, there are good reasons to test to determine which pile will perform best and at what depth. Can the overall number of piles be reduced or does the individual pile capacity need to be reduced and more piles added? Sometimes, it is not the actual load itself that is the main focus of or the reason for the test. Pile supports for a highly sensitive, vibrating, printing press at Tavo Packaging needed to meet very stringent settlement criteria. This information could only be established with a load test. Click to see Tavo Packaging
With more than twenty-four years of helical experience, Danbro is very comfortable providing testing advice and support to owners, engineers, and installing contractors. From our perspective, load tests are a valuable tool. In many cases, we recommend using load tests to determine if we can find a silver lining as demonstrated in the case histories cited above. For more case studies and information on our approach to load testing, click here to see our load test case studies
by Frank D’Angelo, President
Pat Haffert, Vice President