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.
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:
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.
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.