A New Free-Free Resonant Column Device for Measurement of G_(max) and D_(min) at Higher Confining Stresses

摘要

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 (G_(max)) and small-strain material damping (D_(min)). 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 G_(max) and D_(min) under higher levels of σ′_o that are more representative of in situ conditions.