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GRL Engineers Successfully Tests Redesigned APPLE VII System for Helical Pile Load Testing
by Gina Beim
GRL Engineers, Solon, OH, www.grlengineers.com earlier in 2015 reported on the redesign of its APPLE VII dynamic load testing device for helical piles. A Dynamic Load Test consists of applying a limited number of impacts to the helical pile with an appropriately sized drop hammer – in this case the APPLE VII - and taking strain and acceleration measurements, similar to the way the test is performed on other types of deep foundations. The test pile is prepared by placing an impact platform (cushion) to protect the pile head. The APPLE impacts the pile head, and data collected by accelerometers and strain transducers attached to the helical pile shaft is transmitted to a Pile Driving Analyzer® system. Data is then analyzed with the CAPWAP® software, yielding a simulated static load test curve.
The redesign has now been completed and the APPLE VII successfully tested.
Proof loads up to 200 kips (900 kN) can be mobilized on piles founded in rock and maybe one half as much for piles installed in soils. The ram of the APPLE VII weighs 2.1 kips (9.3 kN) and the system allows for a maximum drop height of 6 ft (1.8 m). Being a free drop device, the unit has therefore a maximum potential energy roughly 12 ft-kips or 17 kJ. Other approximate specifications include a total weight of 3,500 lbs (1600 kg), a height of 9 ft (2.75 m) and a footprint of 4 x 4 ft (1.2 x 1.2 m).
The APPLE VII is transported to the job site fully assembled, which makes test setup very quick. However, for loading and unloading a fork lift or similar machine should be on site. The fork lift can then also be used for placing the APPLE VII over the test pile. The ram is raised by a hydraulic system that is part of the APPLE VII system.
The moderate height of the APPLE VII makes it suitable for testing in restricted head room conditions. GRL, while maintaining that it is primarily applicable for helical piles, plans to also use it to load test other relatively small piles such as cast-in-place augered, driven or micropiles.