Imaging a Grouted Column in a Centrifuge Model Using Shear Wave Velocity Tomography

Bender elements embedded in a centrifuge model were used to image a concrete column grouted in sand. The bender elements were oriented in a polar array with the center of the column near the center of the array, and travel-time based tomographic inversion clearly identified the presence of the high-shear wave velocity anomaly. Tomographic imaging was performed using a pixel-based representation, in which the domain is divided into pixels and the shear wave velocity of each pixel is solved by inversion, and using a parametric-based representation, in which the geometry of the domain is assumed and the domain parameters are varied to minimize inversion error. Elimination of time delay present in the system was required to reduce inversion errors. Though the inversion is sensitive to input parameters and data quality, the grouted column was evident in the center of the array for a range of inversion techniques.