Shock Waves in Granular Soil

Experimental and theoretical studies of shock wave propagation in an elastically confined, cylindrical sand column are described. Excitation is produced by an air shock from a pneumatic shock tube, and a special reinforced specimen container is used to restrict radial strains while allowing unimpeded axial motion. Measurements of wave velocity and pressure are made at various stations along the specimen by stress gages embedded in the sand. Test results indicate development of a stable shock preceded by a decaying precursor. Two characteristic velocities are observed: (1) The velocity of the decaying precursor, which depends on confining pressure and relative density; and (2) the velocity of the trailing steady wave form, which depends on dynamic stress amplitude and confining pressure. Theoretical interpretation of test results is presented taking into account the effects of such material characteristics as stress relaxation, a nonlinear stress-strain relationship, and differences between initial loading path and the path of subsequent load cycles.