Development of a new large calibration chamber for testing thickened tailings with the cone penetration test

Abstract

New tailings storage technologies come with new geotechnical characterisation challenges. Additional to the already difficult task of assessing the stability of tailings dams is the frequent requirement of measuring the time-dependent behaviour of tailings. Such time-dependent tailings responses can be monitored using piezometers, which provide continuous data of the pore water pressure within the dam. However, this frequent monitoring must be complemented by in situ investigations. For such in situ testing, the cone penetration test is recommended, mainly because of the useful data that it provides to practitioners, the worldwide availability of suitable equipment, and the rich database of correlations and interpretations available. For the development of these widely used correlations, different techniques have been used in the past including theoretical, numerical and experimental approaches. Since the first two techniques correspond to approximations, experimental data is preferred. These experimental data are usefully derived from calibration chamber testing, which has provided valuable contributions. Since paste and thickened tailings do not generally segregate after deposition, there is an increasing need for developing correlations for cone penetration testing in such materials, which invariably have substantial fines contents. A variety of different calibration chambers have been used for many decades, mainly to create correlations between known soil density, effective stress and saturation conditions. This work presents the development of a new large calibration chamber at the University of Western Australia, the design of which is based on other currently available calibration chambers, but with added capabilities identified as necessary from laboratory characterisation experience of mine tailings within the critical state soil mechanics framework. These include enabling improved tracking of volume changes during saturation and consolidation, as this aspect requires special attention for many thickened tailings materials.