The Seismic Cone Penetration Test (SCPT) is one of several widely used tools for the assessment of the stability of mine Tailings Storage Facilities (TSFs). Its methodology has been developed and used extensively for more than three decades for the in-situ measurement of shear wave velocity (VS), which can be used to infer various soil elastic properties quantitatively. At its core, the method rests on some simplifying assumptions of questionable soundness that undermine confidence in the reliability of its results. In particular, two major uncertainties in the data interpretation process are described in the literature, namely (1) proper identification of the seismic wave travel times, and (2) the accuracy of different data reduction methods. The accuracy in the estimation of VS is important since its values are squared during the calculation of the soil’s elastic constants, and therefore any measurement/estimation error in VS is correspondingly amplified.
3D dynamic full waveform modelling shows that the wavefield excited by a horizontally polarised shear (SH) source is not symmetrical about the axis of the CPT probe. This asymmetry has significant implications for the placement orientation of the SH source relative to the probe, which contains horizontal geophones. Additional wave phases are also generated by the source, and these components also reach the geophones, complicating the seismograms. The 3D shape of the radiated wave field excited during an SCPT test has traditionally not been viewed as an important factor for consideration, but its influence can be significant. Modern computing and forward numerical modelling make 3D simulations of this induced wavefield more accessible, and the validity as well as the assumptions underlying established SCPT practice can be more comprehensively tested.
