Liquefaction Assessment of Deposited Thickened Tailings Using CPTu Soundings Calibrated With Laboratory Testing: a Critical State Soil Mechanics Application

摘要

Application of thickened tailings technologies sometimes require for the impounded tailings to perform as a competent engineered fill (e.g. become the foundation of upstream raises, ensure stability of tailings beach stacked above the dam crest, etc.). In such cases, the geomechanical behavior of tailings is a key issue, with liquefaction often becoming the most influencing aspect. When tailings beaches have a high degree of saturation, stability of the impounded tailings must be demonstrated under post-liquefaction conditions (specially in seismic regions). This requires that liquefaction susceptibility and undrained residual shear strengths of tailings be well understood.To evaluate liquefaction susceptibility of tailings deposits, CPTu soundings are currently the most used tools. Although CPTu can measure the response of tailings associated with their truly undisturbed in-situ state it does not directly provide geotechnical parameters related to tailings behavior. In contrast, while laboratory testing does provide those parameters, they often relate to disturbed conditions. The integration of both CPTu and laboratory data provide a means to characterize tailings behavior for the undisturbed in-situ condition. This paper presented a case study where CPTu and laboratory testing data were combined using the framework of critical state soil mechanics. The differences between completing a liquefaction assessment purely based on CPTu results (i.e., based on average properties of soils and typical correlations for CPTu interpretation) and the assessment of the CPTu results combined with isotropic, oedometer and triaxial compression monotonic paths are presented.