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GRL Engineers Perfects Dynamic Load Testing Services for Helical Piles
by Bill Bonekemper
Much Faster Than Static Load Testing
and Also Less Expensive – As Much as 50% Less
Any foundation contractor understands that time equals money, and the hours that can be shaved from a project bid can provide that much needed competitive advantage. Dynamic load testing of helical piles provides exactly such an opportunity. GRL Engineers, with 10 offices around the USA, (www.GRLengineers.com) has perfected its helical pile dynamic load testing service. The service is a fast, reliable and cost effective method of assessing helical pile deep foundation bearing capacity, and the solution makes it possible to conduct several load tests in a single day – without any reaction piles needed.
“Just as driven piles are tested using dynamic load testing to the ASTM 4945 specification, so can small to large diameter high capacity helical piles, and we now offer this attractive testing service,” said senior engineer Ben White. “We have successfully completed testing on helical pile projects with piles ranging in size from 1.75” up to 12.75” in diameter with bearing capacities in excess of 100 tons. It is also important to note that we typically deliver our initial test results within 24 hours from the completion of testing. In addition to bearing capacity, our dynamic load testing provides information on resistance distribution (shaft resistance and end bearing) and evaluates integrity of the foundation element,” White continued.
GRL has performed dynamic testing on helical piles for projects in several states across the country. As figures 1, 2 and 3 from a project in North Dakota reveal, the dynamic testing process includes a drop weight that varies in mass depending upon the capacity of the helical piles being tested, a frame (in most cases), and an impact platform that is placed on top of the pile. GRL’s instrumentation is attached to the pile between grade and the impact platform. The piles for this project were 7” diameter with two 18” diameter helices, and the factored axial loads were 12 kips at 0.25” of settlement. The average installation depth for these piles was 20 feet, and a 9000 lb. drop weight was used to conduct the testing.
As the graph above from the North Dakota project reveals, each impact creates a load versus settlement curve, and they are superimposed to create the total estimated load versus settlement curve.
The pictures below are from a project located in Texas. The helical piles were 10.75” in diameter with (3) 30” diameter helicies and a total installed pile length of 50 feet. The factored axial resistance was 140 kips at 0.25” of settlement, and a 14,000 lb. drop weight was used to conduct the testing.
“It is interesting to note that the test results from this project indicated some differential movement (slop) at the connection under the first impact. This was addressed after the load test results, but would not have been detectable with a standard static load test (without embedded instrumentation),” White added.
For additional information contact:
Mr. Ben White