Free-field soil response to bidirectional horizontal non-uniform ground motion from multi-point shaking table tests

This paper assesses the dynamic nonlinear free-field soil response under bidirectional horizontal non-uniform excitation through a series of multi-point 1 g shaking table tests. The soil bed was enclosed in an innovative soil box supported by an array of three shake tables and was subjected to uniform and non-uniform ground motions in one and two horizontal directions. The soil response to bidirectional and unidirectional excitations, both uniform and non-uniform, were compared and discussed in terms of acceleration time history and Fourier spectra, acceleration amplification factor and soil settlement, as well as shear stress-shear strain behavior. The comparison of soil responses to bidirectional and unidirectional shakings demonstrated that the trends of peak acceleration amplification factors are similar along soil depth, but the response difference between bidirectional and unidirectional shaking is increasingly higher along the soil profile towards the ground surface, especially for uniform excitation. The variations of soil settlement, shear stress-strain and damping curves under bidirectional excitation were similar to that under longitudinal excitation; however, they were much different than those observed under transverse excitation. The soil damping in Y-direction under non-uniform excitation was larger than that under uniform excitation. These different site response characteristics under bidirectional non-uniform excitation should be properly considered in the seismic design of extended infrastructure. •Soil was loaded with bidirectional (BD) and unidirectional (UD) excitation.•Response difference between BD and UD shaking increases as site depth decreases.•Soil surface fluctuated more intensely under non-uniform excitation.•Energy dissipation caused by Y-direction motion was 7–15 times that of X-direction.