A research program is described for measurement of the shear behavior of geosynthetic clay liners (GCLs) and GCL interfaces under dynamic loading conditions. A state-of-the-art, large-scale dynamic direct shear machine is currently being constructed for the project that has the capability to test rectangular GCL specimens measuring 0.3 × 1.1 m (12 × 42 in.). The device has a maximum shear displacement of 254 mm (10 in.), a maximum normal stress of 2,400 kPa (50,000 psf), a maximum shear stress of 750 kPa (15,700 psf), and the capability to impart sinusoidal shearing with a displacement amplitude of 25 mm (1.0 in.) at a frequency of 5 Hz. This paper describes the objectives of the research program, the equipment under construction, and the dynamic shearing tests to be conducted. Copyright ASCE 2005.