The resonant column’s ability to measure soil stiffness at small strains with enough strain variability to measure the upper portion of the modulus degradation curve within soils, makes it an extremely attractive apparatus for testing unsaturated soils. A high air entry porous stone is fitted into the base pedestal, and pore air and water pressures are applied in the same way as a triaxial test. Note: A GDS resonant column apparatus can be upgraded to become an unsaturated RCA at any time.
