LABORATORY STUDY OF SEISMIC FREE-FIELD RESPONSE OF SAND

This paper describes a new soil-structure interaction test box for use on a moderately large shaking table. The test box is designed to repl icate, as nearly as possible, the free-field seismic response of a soi l layer overlying a rigid base. Results from shaking table testing are presented which demonstrate the ability of the test box to serve as a large-scale shear device. The test box is unique in its ability to de termine dynamic shear modulus for both high- and low-amplitude shear s train, and also to study the dynamic response of sand under low levels of confining stress. Dynamic shear modulus for standard Ottawa sand w as measured over a wide range of shear strain amplitude and compared w ith data from the existing literature. Finally, based on results from the test box, a constitutive model is proposed which describes the fre e field response of a sand layer overlying bedrock and subjected to ve rtically propagating SH waves. The model is simple in form with a sing le parameter uniquely related to the friction angle of the sand.