Proposed ASTM Standard for the Stokoe-type Resonant Column Torsional Shear Device

Resonant Column Torsional Shear (RCTS) testing has become one of the most commonly used methods for determining laboratory soil stiffness and soil damping. The RCTS test has been accepted and is commonly utilized during the permitting of new nuclear facilities. However, there is still no available public standard for performing RCTS tests using the Stokoe-type device. Therefore, an ASTM standard for calibration and performance of RCTS tests using the Stokoe-type RCTS device is presented herein. Data collected using the Stokoe-type RCTS devices at the University of Arkansas (UofA) and at the Norwegian Geotechnical Institute (NGI) also aided in the development of this standard. By following the proposed standard to calibrate the RCTS Stokoe-type device, the mass polar moment of inertia value, Jo, for the UofA drive plates were found to be similar but smaller than to Jo values found by other authors. The proximeter calibration factor, KP, was determined to be valid because the obtained results were consistent for the linear calibration method and for the rotational calibration method (0.0028 rad/V). The torque calibration factor, KT, was also determined to be valid with the obtained value of 0.1347 N·m/V. To validate the proposed ASTM standard, RCTS tests following the standard were performed on Ottawa Sand specimens using the Stokoe-type devices at the UofA. The obtained modulus reduction curves and damping curves were compared with curves developed at the University of Texas. The UofA obtained modulus reduction curves were found to plot at higher values than the Texas curves, but both curves followed the same trend. The UofA damping curves compared well with the Texas curves at shear strain levels less than 10-2 percent, but it was above the Texas obtained curves at shear strain levels greater than 10-2 percent. Shear wave velocity values for the Ottawa Sand specimens from the RCTS tests were also compared with results obtained from bender element test performed on similar specimens at the same confining pressure. A only five (5) percent difference in shear wave velocities was observed between the bender element obtained values (178 m/s) and the resonant column obtained values (187 m/s)