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Torque Monitoring Equipment Overview
In an effort to assist the installers of helical piles, HPW has begun compiling data on various types of equipment. As we continue to acquire this data, we will share it with you.
Knowledge of installation torque is crucial for many helical pile applications. The load bearing capacity of a helical pile is directly correlated to the torque required to install the pile. For a more technical discussion of the torque to capacity relationship please see Dr. Howard Perko’s paper on the subject. It behooves installers and engineers alike to have accurate equipment on site to ensure a well engineered helical foundation is installed to the specifications set forth by the engineer. This requires an accurate torque monitoring device or method.
Here are some of the different devices & methods for monitoring torque along with some pros and cons for each:
Shear Pins
Pros – Simple to use. Durable. Almost idiot proof. Generally pretty accurate.
Cons – Does require some regular maintenance. The installer is “blind” in-between shear pins. Underground obstructions can shear all of the pins at once leaving the installer with no reliable torque data.
Single Direction Hydraulic Pressure
Pros – Easy set-up and simple operation.
Cons – Hardly accurate. Somewhat pricey. Torque is empirically derived. Torque drive must be periodically re-calibrated.
Differential Hydraulic Pressure
Pros – Easy set-up and simple operation. Fairly accurate.
Cons – Somewhat pricey. Torque is empirically derived. Torque drive must be periodically re-calibrated.
Mechanical Torque Bar Indicator
Pros – Measures pure torque. Highly accurate.
Cons – Heavy. Very expensive. Not durable.
Strain Gauges
Pros – Highly accurate.
Cons – Expensive. Torque is empirically derived.
Optical Strain Gauge
Pros – Inexpensive.
Cons – Not very accurate.
Shaft Twist
Pros – Doesn’t get any cheaper or easier.
Cons – More of an approximation. Subjective. Not scientific. Only works with square shafts. Inconsistency from shaft to shaft.
Again, knowledge of installation torque is crucial for many helical pile applications. Each of the above devices and/or methods has pros and cons. Each solution or a combination of two or more should be considered as a means to measure installation torque.