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Resonant Column Apparatus (Hardin Type)

Product Code : H-RCA

Hardin Type Resonant Column Apparatus (H-RCA) is a system that allows samples to be tested in resonance while maintaining an anisotropic loading up to 2kN. This is achieved by a slender, thin walled loading column passing through the drive system to the topcap. The GDS Hardin Oscillator contains an electro-magnetic drive system incorporating precision wound coils and composite sintered neodymium iron boron (NdFeB) “rare-earth” magnets.

The GDS Hardin Oscillator can be mounted in a standalone system with an integral axial force actuator (shown opposite) for post resonance testing up to 5kN.

Discover more resonant column equipment for soil testing.

Resonant Column Apparatus (Hardin Type)
specification datasheet (PDF)
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Key features Benefits to the user
Hardin Type Oscillator:
 The specific benefit of the Hardin Oscillator is the ability to perform torsional resonance anisotropically.
Hardin Oscillator can be loaded beyond its useable load:
The Hardin head is designed to be able to apply up to 2kN axial force whilst still being able to perform resonance tests. The GDS head is designed such that the load cell can be loaded beyond this value to 50kN, allowing a full suite of triaxial tests to be performed to shearing post resonance.
Choice of two systems, one to 5kN axial load and one to 50kN axial load:
 The 5kN max load system is neat because it has an actuator built into the top of the cell. The cell is a hybrid style cell that allows the cell wall to be lifted clear of the sample while the top-cap is supported in place for easy and accurate sample installation and alignment. The 50kN version (using a traditional load frame) has the obvious benefit of the additional load that can be achieved post resonance, however it does not have the advantage of a hybrid cell and has a traditional removable cell top instead.
Integrated reaction mass:
 The reaction mass is integrated into the drive system so it is as close to the force generation as possible. This eliminates uncertainties due to transferal of forces.
Current driven using a transconductance power amplifier:
 The impedance of magnet / coil devices change with frequency. At higher frequencies, using a constant voltage amplifier the current would be seen to reduce. As the torque is directly proportional to current, the torque will also reduce and a non-linear torque input would affect results. This effect is removed in the GDSRCA by using a current driven power amplifier.
Dedicated GDS RCA software is used for control and data acquisition of the apparatus:
 Simple automated tests allow tests to be consistent.
Accuracy of Pressure Measurement
0.15% FRO
Dimensions

1005mm (H), 330mm (W) (500mm with valves)
Load Range (kN)

2 kN
Operating Frequency (Hz)

0-300
Pressure Range (MPa)

1, 2 MPa
Sample Sizes

50, 70, 100mm
Weight Approx (kg)

128 (Approx)
  • Vertical Bender Elements
  • Torsional Shear (slow speed torsional shear test) upgrade

 

Tests supported by the Resonant Column Apparatus (Hardin Type), resonant column equipment for soil testing :-

B Check

The B-Check is a pre-test to check that the specimen is sufficiently saturated by measuring the Skempton pore water pressure parameter B. The cell pressure is increased to the specified value whilst the back pressure remains on hold volume (i.e. the undrained state). The system compares the change in pore pressure (Δu) caused by the increase in cell pressure (Δσ3). The value of B is calculated as Δu/Δσ3.  If your GDS triaxial testing system has a cell pressure controller and a pore pressure transducer, then the B-check is automated within the GDSLAB software. Please note: Some apparatus may require additional components or software modules to perform certain tests.

B Check soil test equipment
Consolidation (Triaxial)

Consolidation simply applies a constant cell and back pressure to the sample whilst monitoring the volume change within the sample. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Consolidation (Triaxial) soil test equipment
Constant Head Permeability

The constant head test simply maintains a constant differential in pressure between the top and the base of the specimen (top pressure is always set higher than the base pressure). The flow is then measured on the top controller and the base controller.  Please note: Some apparatus may require additional components or software modules to perform certain tests.

Constant Head Permeability soil test equipment
Constant Rate of Flow Permeability

The constant rate of flow test simply maintains a constant base pressure whilst applying a constant flow through the top of the specimen. A maximum hydraulic gradient can be set which will pause the rate of flow if the pressure differential between the top and the base of the sample gets too large.  Please note: Some apparatus may require additional components or software modules to perform certain tests.

Constant Rate of Flow Permeability soil test equipment
Maximum Shear modulus

Determination of the maximum (i.e., very small strain) shear modulus of a specimen. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Maximum Shear modulus soil test equipment
Slow Speed (up to 2Hz) Torsional Shear (TS) testing

The damping ratio is a measure of describing how oscillations in a system die down after a disturbance i.e. how the shear waves generated in the sample die down after a test is complete. This test can be carried out in torsion or flexure through the resonant column. Please note: Some apparatus may require additional components or software modules to perform certain tests.

Slow Speed (up to 2Hz) Torsional Shear (TS) testing soil test equipment

Standards for the Resonant Column Apparatus (Hardin Type), resonant column equipment for soil testing :-