ShearTrac-II operates as an intelligent loading system. It uses feedback from transducers to provide real-time control of the load frame. Two force transducers (horizontal and vertical) and two displacement transducers (horizontal and vertical) are the sensors for the ShearTrac-II unit. The computer loads or unloads the load frame until the readings from the transducers equal the values required to meet the test specifications. The loading mechanism to apply normal loads is raised and lowered by a micro-stepper motor connected to a worm gear. The loading mechanism to apply shear loads is moved left and right by a second combination of micro-stepper motor and worm gear. Limit switches for both horizontal and vertical motions prevent running the loading mechanism beyond its physical limits.
The standard ShearTrac-II unit uses a 24-bit A/D card. This means that the raw data reading units are on an integer scale from 0 to 65536 (0 to 216). Each reading unit is also called a count. These count readings must be converted to engineering units. The system is supplied with calibration factors that do this conversion. The system uses calibration data to relate count readings to engineering units. Because ShearTrac-II is an intelligent loading system, all components must be functioning correctly for the system to operate. All operation of the load frame must occur through the computer for full automation. Separate manual operation is possible through front panel keypads. To avoid damage to any component, readings from all sensors are checked by the computer hundreds of times per second. Any analog or digital reading outside the acceptable condition prevents the micro-stepper motors from running.
The computer and monitor are used for displaying test results in real time, and for editing test results and producing a report after the test has been completed.
Manual control for both vertical and horizontal motion of the ShearTrac-II load frame is achieved with keypads and easy-to-use menus. The software which runs a test allows the user to define the conditions for running a particular test by way of self-evident information entry windows.
ShearTrac-II requires no special skills to operate, other than those used in conventional consolidation testing. A person familiar with soil testing can learn to use the system confidently within a few hours. Familiarity with using Windows can significantly reduce the learning time.
A ShearTrac-II unit can be configured to run direct shear, residual shear, direct simple shear, cyclic direct, simple shear, and incremental consolidation testing.