EMBEDDED INSTRUMENTATION FOR COUPLED SHEAR STRAIN- PORE PRESSURE RESPONSE IN MULTIDIRECTIONAL SHAKING TABLE TEST

A new instrumentation system was developed and implemented on a biaxial laminar shear box for modeling the free-field response. The main purpose of the instrumentation is to measure the coupled shear strain-pore pressure response of saturated sands subjected to multidirectional shaking. A lowfrequency triaxial accelerometer and a miniature piezometer were integrated in a small case to measure the local particle motions and pore pressure variations. Four integrated sensors were deployed to form a square instrumentation array on the plane parallel to the wave propagation direction. Embedded sensors were installed during the sample preparation stage and were acquired by a high-speed data acquisition system capable of synchronizing with other instrumentation system. Four shear strain evaluation methods, which use either the particle displacements or the particle velocities computed by integrating the acceleration data numerically, were implemented to calculate the shear strain time-histories at locations with simultaneous pore pressure measurements. In addition, relative displacements of box frames were used to calculate average shear strains of soils confined between frames. Series of shaking table tests with different acceleration amplitudes, frequencies, durations, and shaking directions were performed on a saturated clean sand. Comparisons among shear strains evaluated by embedded sensors and relative displacements of frames are conducted to verify the performance of the embedded instrumentation and to assess the boundary effects of the laminar shear box. Coupled shear strain-pore pressure behaviors in liquefied and nonliquefied cases are presented and discussed. More insights of the interactions between the induced shear strain and generated excess pore pressure are shown.