Soil & Aggregate

The GDS Resonant
Column Apparatus (RCA)
Relevant Technical Papers

Relevant HelpsheetsCompatible
 Software: gdslab,
What is it?
The GDS resonant column apparatus is used to excite one end of a confined solid or hollow cylindrical soil specimen. The specimen is excited in torsion or flexure (bending) by means of an electromagnetic drive system. Once the fundamental resonant frequency is established from measuring the motion of the free end, the velocity of the propagating wave and the degree of material damping are derived. The shear modulus is then obtained from the derived velocity and the density of the sample.
Outline Specification
  • Standard cell capable of 1 MPa gaseous cell pressure (other cells available up to 25MPa).
  • Electromagnetic drive system incorporating precision wound coils and composite Sintered Neodymium Iron Boron (NdReB) "rare-earth" magnets.
  • Inner cell for silicon oil (to aid membrane sealing).
  • Energisation mode of coils is switchable by software to provide torsional and bending tests (longitudinal).
  • Internal LVDT for measurement of sample deformation.
  • Internally mounted, counter-balanced accelerometer.
  • 1 off Drive amplifier for RCA motor.
  • 1 off high-speed 16-bit data acquisition/control card with associated GDS RCA control box and interface panel.
  • 1 off computer controlled proportional gas valve to control cell pressure from software.
  • 3 off calibration bars of differing stiffness' and calibration weights.
  • Back pressure by GDS Standard pressure/volume controller
  • Options for environmental temperature chamber (-20 degs C to +40 degs C) and an axial loading actuator and frame.
GDS-RCA Software
GDS-RCA software is used for control and data acquisition of the RCA apparatus. The software allows testing to occur via a simple, user-friendly interface. The tests that may be performed using the GDS-RCA software are as follows:
  • Resonance in torsion.
  • Resonance in flexure.
  • Damping Ratio in torsion.
  • Damping Ratio in flexure
  • Slow speed (<2Hz) torsional shear
GDS-RCA Resonance Test Data
When performing Damping Ratio tests, the apparatus was designed to minimise equipment damping. During free vibration decay (after the power is normally shut off at resonance) 'back' EMF is usually generated in the coils by the movement of the magnets, this causes large equipment damping errors. In the GDS resonant column the software can switch the hardware to provide an 'open circuit' through the coils during free vibration decay, which prevents 'back' EMF generation.
GDS-RCA Damping Test Data
A software video CD is available which demonstrates the use of the GDS-RCA software. This CD as with other GDS software and hardware demonstration CD's are available on request.
Torsional / Flexural Vibrations
During torsional tests, four pairs of coils are connected in series so that a net torque is applied to the sample. To apply flexural vibrations, the coils are switched (automatically) so that only two magnets are used applying a horizontal force to the specimen hence inducing flexural excitation. This allows the same coil and magnet arrangement to be used in both flexural and torsional vibration.
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