Volume 28, Issue 2 (March 2005)
A New Free-Free Resonant Column Device for Measurement of Gmax and Dmin at Higher Confining Stresses
The fixed-free resonant column device has traditionally been used to measure shear modulus in laboratory soil and rock specimens. It is a proven method that provides measurements over a range of shear strain and effective confining stress (σ′o), but the test relies on a specialized system of coils and magnets. The free-free resonant column device is a simpler device that allows for measurement of small-strain shear modulus (Gmax) and small-strain material damping (Dmin). However, σ′o in the free-free device has traditionally been limited to a maximum attainable vacuum pressure of around 80 kPa, because the test has not been configured in a pressurized cell. Therefore, a new free-free device was developed to allow measurements in a pressurized cell with σ′o greater than 80 kPa, while remotely exciting the specimen with a rotary solenoid. Test results demonstrate its potential for measuring Gmax and Dmin under higher levels of σ′o that are more representative of in situ conditions.