Results of a dilatancy round robin

The critical state approach currently finds widespread adoption in geotechnical engineering practise, particularly with respect to tailings storage facilities. The laboratory component of such works usually involves determination of the critical state line (CSL) followed by stress- and state-dilatancy behaviour in triaxial compression conditions, characterised by the volumetric coupling parameter N tc and the state dilatancy constant χ tc . While the reliability of CSL testing using current state of practise methods has been recently demonstrated, it is currently unclear how reproducibly N tc and χ tc can be obtained. To investigate this, a dilatancy round robin programme was carried out by five laboratories who regularly carry out such testing. In the first stage of the programme, each laboratory adopted a version of ‘densification in layers’, either dense moist tamping or vibration-densification. While a generally consistent N tc was observed, significant variation in χ tc was seen. To further investigate this variation, a second stage was carried out where slurry deposition and the ‘air-dried’ technique were used. These techniques showed better agreement between laboratories, while also producing lower values of χ tc than densification in layers. Some potential implications of these observations on current tailings engineering laboratory testing practise are outlined.