The capacity of a pile can be correlated to its installation torque. This torque-to-capacity relationship for helical anchors and piles is an empirical method originally developed by the A.B. CHANCE Company beginning in the late 1950s. Today, the relationship is well recognized in the deep foundation industry. It is commonly referred to as torque correlation.
As a helical anchor (tension applications) or helical pile (compression applications) penetrates deeper into increasingly dense or hard soil, torque correlation predicts an increase in installation energy or torque. Also, the higher the installation torque, the greater the axial capacity of the installed pile. Therefore, engineers can better understand the capacity of helical anchors/piles in the soil by taking torque measurements.
Traditional Torque Measurement
The most common torque measurement methods include measuring shaft twist, or wrap in the shaft when installing Square Shaft type helical anchors, using a differential pressure transducer to measure the pressure drop across a hydraulic torque motor; or using the shear strength of torque limiters (shear pins) in order to figure out torque-to-capacity.
While shaft twist and torque limiters work well enough, their precision leaves something to be desired, and none of them offer continuous readings that allow engineers to measure torque as conditions change. Differential pressure transducers work well, but they must be carefully matched & calibrated to the installation machine and torque motor.
The Benefits of CHANCE® wireless torque indicator
The CHANCE® wireless torque indicator is a continuous reading indicator that can overcome significant problems posed by traditional devices such as providing precise, real-time data. Its features and benefits include:
Compared to the traditional devices, the system helps prevent any excess torsional loading with potential to damage a pile. With such a device, it's possible to pre-determine required torque values ahead of time and install helical anchors/piles accordingly. Therefore, the user already has a good idea of a specific pile's holding capacity in the soil.
Moreover, it is easier to use, thanks to its simple design. The strain gauges measure the shear strain in the torsion bar as the helical anchor is installed. The signal from the strain gauges is converted to torque in ft-lb or N-m.
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The installation manuals of CHANCE Torque Indicator with Wireless Smart Device App Connectivity Model No. C3031836 and CHANCE Digital Torque Indicator Model No. C3031689NR are linked below.
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