Ring Shear

The Geotechnical Laboratory at Virginia has eight ring shear devices fabricated by Wykeham-Farrance now Controls Group, and modified to reduce side-wall friction. The normal stress in this device is applied by means of dead weights using a 10:1 ratio lever arm. The test specimen is compressed in between two sintered bronze or carborundum end platens to allow drainage. The axial displacements are measured using an LVDT located above the top platen. To shear the test specimen, the test specimen container rotates and the top platen reacts against two proving rings or load cells that measure the force required to prevent movement. The proving rings are positioned in opposite directions forming a 90° angle with the reaction arm from the top platen. The end platens attached to the bottom of the test specimen container and top platen are serrated to prevent slippage from occurring at the soil-end-platen interface. The rate of displacement is controlled by a set of gears or a microprocessor controlled drive system that allows the test specimen to be sheared at a constant rate of displacement. This device allow the sample to be subjected to infinite displacement on the same failure plane and in the same direction.

In some of the devices, the proving rings and LVDT are connected to a Keithley 2000 multimeter data acquisition system that records the change in voltage of these devices in response to the change in load and vertical displacement of the test specimen. This information is processed and converted to engineering units using a proprietary computer program developed at Virginia Tech.

In the newer devices, the sensors are connected to a GEODATALOG system and software provided by Controls Group.

Specifications:

• Inner and outer diameters of 2.76 inches and 3.94 inches, respectively.
• Specimen height about 0.2 inches.
• Displacement rate from 0.001 to 180 deg/min.