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Verifying Soil Capacity With Torque Monitored Installations

To help homeowners and professionals understand the importance of torque monitoring we will briefly review some history of torque monitored screw pile installations as well as the benefits of Postech’s long-term & dependable foundation system.

Monitoring torque during screw pile installations determines soil capacity by essentially creating a geotehnical report (soil test) for every pile.  This effective approach decreases liability for engineers and building officials across Ontario and the rest of Canada.  We will discuss the history and benefits of torque monitored installations vs traditional methods.

Torque monitoring of screw piles during installation has become the standard and is considered to be best practice after years of research and testing since the 1980’s.  The correlation between torque and ultimate capacity has been proven to be the most accurate method at predicting load capacity of a pile.

To show how long this method has been proven, we will discuss a study from the 1980’s that was conducted by professionals Sam Clemence (a professor at Syracuse University) & Bob Hoyt (a consulting engineer).  These two gentleman discovered a correlation between installation torque and helical pier capacity by conducting 91 full-scale load tests and comparing the data to torque monitored installations.  They found that torque monitoring of helical pile installs was even more accurate than the theoretical/computational method of calculating bearing capacity.  This study was formalized by Clemence and Hoyt in a research paper in 1989 and is referenced in numerous helical pier technical articles and books world wide.  (Installation Torque as a Predictor of Helical Pile Axial Capacity (2007) – helicalpileworld.com)

One major factor when monitoring torque is to ensure the installer is using proper installation equipment such as an anchor drive and not an auger drive.  We will discuss in a future blog, the difference between a professional and DIY installation explaining how load bearing capacities can be cut in half with a poor installation of screw piles.  Keep checking back for new blogs!  For now, here’s the difference between the two drive motors:

Anchor Drive – a high torque motor designed to slowly advance a helical pile one pitch of the blade per revolution.  Usually 10-30 rpm.

Auger Drive – a high speed motor designed to churn soil at high rpm.  (post-hole augers)

There are numerous methods for measuring torque during helical screw pile installation, some of these methods include:  mechanical dial indicator, digital devices such as Digga-Align, Intelli-Tork or Torque-Pin, shear pins, anchor drive refusal, hydraulic pressure differential, etc.  These methods do vary in levels of accuracy and allowable load charts may be adjusted by engineers for safety of factor.

“The empirical relationship between installation torque and capacity is considered to be the greatest attribute of helical foundations.” – Helical Foundations… What an Engineer Needs to Know, Structure Magazine (June 2004), Gary Seider, P.E.

A professional company equipped with torque monitoring such as Postech Windsor generally works with brand specific engineered allowable loads charts.  These engineered charts provide allowable loads for the piles based on torque values achieved.  The engineer providing the stamp on the allowable loads charts does not limit their liability to one specific soil value assumption but rather the entire range of torque to capacity values included on the chart; these values may range from 2,000lbs to 50,000lbs or greater.

Engineers and building authorities across Canada and United States have moved away from blind installation methods as they are understanding the essence of torque monitoring to ensure adequate bearing capacity of the soil.  We hope this post helps you make the right decision when planning your next building project.  Customers insisting on torque monitored installations of helical screw piles greatly reduce the possibility of pile failure.  If you want a foundation that will last a lifetime, contact Carmine at 519.551.5581 or windsor@postech-foundations.com for more information about our galvanized Thermal Piles.

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