Experimental studies of seismic soil pressures on vertical flexible, underground structures and analytical comparisons

Seismic soil pressures are critical analysis components to understand and design for soil-structure interaction of sub-surface structures. A large scale experimental research program conducted at E-Defense's Shake table in Miki, Japan, included unprecedented seismic soil pressure measurements on a vertical, flexible, hollow shaft with model scale dimensions of 0.8 m square and 7.0 m in height. The densely instrumented vertical shaft was part of a larger system of underground structures, placed in an 8.0 m diameter laminar soil box. The two-layer soil stratigraphy consisted of an upper layer of medium dense sand and a lower layer of simulated bedrock. The hollow vertical shaft was constructed of aluminum and scaled to 1/20th of its prototype dimension. Two-directional, scaled ground motions of the 1995 Kobe earthquake were applied via shake table loading and seismic pressures were recorded using contact pressure sensors. Experimental results, including a dynamic system characterization, site response analyses, pressure time histories, and seismic pressure distribution profiles provide a critical benchmark for imminent numerical studies and the advancement of seismic soil pressure models for flexible structures. Following a thorough review of soil pressure analysis methodologies in literature, a detailed description of the large scale test and experimental results is presented. A comparison with limit state and elastic-based analytical approaches for retaining walls found in literature showed that, despite the unique shaft geometry, analytical methods accounting for the structural flexibility were able to closely predict the experimental soil pressures, while methodologies derived for rigid subsurface elements can only serve as rough preliminary estimate and should not be employed in performance based geotechnical analyses.