Resonant Column and Torsional Shear Tester

It measures the small-strain dynamic properties of a soil specimen: shear wave velocity, shear modulus and damping ratio.

Two test modes share one device. The resonant column test finds the fundamental frequency of the specimen under torsional excitation; the torsional simple shear test loads it directly and reads the stress-strain response.

Both are used where the design depends on how soil behaves under vibration rather than under static load.

Resonant frequency, shear wave velocity, shear modulus, shear strain, and damping ratio by two independent routes: half power bandwidth and free vibration decay.

Having damping from two methods on the same specimen is useful because they disagree in a revealing way when the specimen or the fit is poor.

In torsional shear mode the secant shear modulus comes from the stress-strain response and damping from the hysteresis loops. Excitation covers 1 to 300 Hz in resonant column mode and 0 to 50 Hz in cyclic torsional mode.

The resonant column test excites the specimen and finds the frequency at which it resonates, from which the shear wave velocity and modulus follow.

The torsional simple shear test applies a controlled torsional load and reads the response directly, which gives modulus and damping from the loop rather than from a frequency.

RC works at very small strains, TSS reaches larger ones. Running both on one specimen is how a stiffness degradation curve is built without changing samples, which is the reason the two are combined in a single unit.

By a current-driven electrical motor mounted on an internal floating frame inside the cell, using four NdFeB magnets of 10 by 25 by 40 mm and eight coils.

Mounting the motor on a floating frame is what allows large angular and axial deformation without the drive fighting the specimen's own movement.

Torque comes from current, so the excitation is controlled electrically rather than mechanically, which is what makes the frequency sweep possible. Maximum torque is 1 Nm and maximum angular deformation 10 degrees.

50 mm diameter specimens as standard, with 38 mm available on request.

The cell is an aluminium construction with stainless steel columns and a transparent acrylic cylinder of 170 mm internal and 200 mm external diameter, with channels for bottom drainage.

Test accessories for the specimen sizes are part of the supplied package: contact us if your programme needs a size outside these.

Up to 1 MPa, applied through an electro-pneumatic cell and back pressure control system that is part of the unit.

Confining pressure is not a side condition in this test. Shear modulus rises with effective stress, so the measured stiffness is only meaningful alongside the pressure it was measured at.

That is why the pressure control is integrated rather than left to an external panel, through two electro-pneumatic converters driving cell and back pressure from the main control box.

Yes. Automatic detection of the fundamental frequency is a built-in feature, so the operator does not sweep manually and judge the peak by eye.

That matters for repeatability. A resonance peak read slightly off shifts the shear wave velocity, and the modulus follows the square of that velocity.

An integrated signal generator and oscilloscope are part of the unit, so the excitation and the response are handled in one place rather than through separate instruments.

The cell with its columns and acrylic cylinder, test accessories for the specimen size, the internal floating frame with the torsional motor, and the main control box.

The control box carries the power supply and the current amplifier that drives the motor, along with the signal conditioning for the transducers and the data logger.

Optional additions are a MEMS accelerometer for the sensor kit and a calibration kit of two calibration bars and two calibration weights.

In seismic design and vibration problems: site response analysis, machine foundations, pile design under dynamic loading and liquefaction assessment.

All of these need stiffness and damping at strains far smaller than a triaxial or shear box test reaches, which is the gap this device fills.

Where the same project also needs static strength parameters, the rest of our soil mechanics equipment covers that side.

Field methods measure the ground as it is, including its structure and stress history, but at a single condition and a single strain level.

The laboratory device measures one specimen while you control confining pressure and strain amplitude, which is how the stiffness degradation curve behind a site response analysis is produced.

The two are complementary rather than alternatives, and most seismic design work uses both: the field measurement fixes the in-situ stiffness, the laboratory device supplies the curve it sits on.

Specimen diameter, the confining pressure range your programme needs, and whether the work requires torsional shear as well as resonant column results.

The standard configuration covers 50 mm specimens at up to 1 MPa, which fits most site investigation work.

Send your project scope and we will confirm the configuration: request a quote.

Yes, and on this device it earns its place. Specimen mounting and the fit between specimen and drive plate affect the resonance more than any software setting.

The session covers mounting, pressure setup, running a frequency sweep and interpreting the two damping results against each other.

To arrange it on your own soils, contact us.