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GRL Engineers Conducts First Known Dynamic Load Tests on Two Chance® Helical Pulldown MicropilesTM
by Bill Bonekemper
GRL Engineers (www.GRLengineers .com), with ten offices offices located around the U.S.A., has performed dynamic load testing of helical piles on many projects. However, the first known dynamic load tests conducted on the Chance Helical Pulldown Micropile was recently completed in Jersey City, NJ. when two piles were tested.
The (105) piles for the project were installed by Chance certified installer, McAuliffe Contractors, LLC (www.mcauliffecontractorsllc.com) with headquarters located in Kenilworth, NJ. The specified piles were Chance 1.75” RCS with 8”,10”,12”,14” helical bearing plates. The piles were installed to an average depth of (79) feet, and the first (15) feet of each pile included a 6” PVC casing due to an abundance of fill material and organics on the site. Because of these fill conditions, pre-drilling was required on many of the piles prior to installation. The design load requirement for the piles was (20) tons.
For additional information contact:
Alex Ryberg - ARyberg@GRLengineers.com
Ben White - BWhite@GRLengineers.com
Dynamic Load Test System (APPLE) was Delivered and Two
Load Tests were Successfully Completed in One Day
The dynamic load test system called APPLE, consisting of a drop weight and a frame, is delivered to the job site and placed in position over the test pile by the McAuliffe crew using a crane. Positioning and securing APPLE is a relatively easy and fast process, and this makes it possible to conduct multiple load tests in a single day - with no reaction piles required.
Once APPLE is secured over the test pile, instrumentation that measures and transmits the test data is attached to the pile. A Pile Driving Analyzer® (PDA) is then connected to the instrumentation to record and store the data when the (9) kip weight is dropped onto the pile.
About Dynamic Load Testing
Dynamic Load Testing is a fast, reliable and cost effective alternative to evaluating foundation bearing capacity by performing static load tests. It is often possible to conduct several dynamic load tests in a single day. In addition to bearing capacity, dynamic load tests (which are standardized by ASTM D4945-12 Standard Test Method for High-Strain Dynamic Testing of Piles) provide information on resistance distribution, making it possible to identify the portion contributed by shaft resistance versus end bearing.
A dynamic load test consists of impacting the top of an instrumented foundation with a substantial ram mass, which causes the foundation element to experience a small permanent set. The instrumentation consists of accelerometers and strain transducers. Data collected by these sensors is transmitted in real time to a Pile Driving Analyzer® (PDA) dynamic testing system, yielding several results as the test is taking place. Field test data is further analyzed with the CAPWAP® software. When running a CAPWAP analysis, an engineer models the pile and the soil, iteratively refining the model until an optimal solution is found. At that point, the program outputs a simulated static load test in the form of a calculated load-set curve, among other results.
The load bearing capacity of helical piles may be evaluated by high strain dynamic tests, with some adaptations designed to accommodate their special characteristics. A limited number of impacts is applied to the helical pile with an appropriately sized, custom built drop hammer. During CAPWAP analysis, the geometry and behavior of helical piles must be adequately modeled.
Construction is now well underway for the new building.
HPW would like to extend a special thanks to Mr. Tom McAuliffe, president of McAuliffe Contractors, for providing the photographs and helical pile installation information for this article.