ABSTRACT
Seismic Cone Penetration Testing (SCPT) is an important geotechnical testing technique for site characterization that provides low strain (< 10−5) in-situ interval compression (Vp) and shear (Vs) wave velocity estimates. Baziw Consulting Engineers has invested considerable resources in advancing the art of SCPT, and in this paper a newly developed Normal Moveout Seismic Cone Tomographic Testing (NMO-SCTT) algorithm is introduced. This algorithm allows for two dimensional imaging of the subsurface stratigraphy by processing acquired seismic trace arrival times derived with increasing source-sensor radial offsets. This dramatically increases the ability to characterize near-surface stratigraphy, which is very important for accurate liquefaction assessment. As opposed to crosshole tomography, the NMO-SCTT does not require any significant site disturbance aside from a single SCPT sounding, thereby greatly reducing the cost and the environmental impact. This paper outlines the mathematical and algorithmic details of the NMO-SCTT algorithm, which builds upon BCE’s established FMDSM algorithm. As such it incorporates Fermat’s principle when estimating SCPT interval velocities. In addition a real SCPT data tomographic data set is presented using SCPT seismic data that was acquired at offsets of 1.85 m, 5 m and 10 m, and down to a depth of 20.5 m.
