During the afternoon of the 9th of March 2018, a mobile slump occurred in an approximately 300 m section of the southern embankment of the Cadia Valley Operations (Cadia) Northern Tailings Storage Facility (NTSF), located in central-west New South Wales, Australia. The embankment slump resulted in a release of tailings from the NTSF, with the released tailings captured within the adjacent South Tailings Storage Facility (STSF). Cracking (on the embankment crest) and thrusting (at the embankment toe) observed by Cadia site personnel earlier in the day enabled timely evacuation of the worksite, along with some downstream residential homes, prior to the slump occurring. This resulted in the slump creating no obvious social or environmental impacts.
An Independent Technical Review Board (the ITRB) was established to determine the technical causes of the Cadia NTSF embankment slump. The ITRB reported on its findings on the 17th of April 2019 (Jefferies et al., 2019), concluding that a previously unidentified low-density foundation layer in the vicinity of the slump had progressively deformed due to loading imposed by the embankment construction. When the rate of this deformation rapidly increased, tailings impounded within the NTSF liquefied, significantly increasing the load pushing on the embankment. The already-weakened foundation was ultimately unable to resist this increase in load, resulting in the embankment slumping.
This case study briefly summarises some of the geotechnical engineering findings reported by the ITRB. Specifically, it focuses on aspects of the advanced laboratory testing programme conducted during the investigation, for which advanced monotonic and cyclic direct simple shear, triaxial, bender element, and constant rate of strain apparatuses designed and manufactured by GDS Instruments (GDS) were used. We strongly recommend that our readers refer to the publically available ITRB report, published by Newcrest Mining Limited (NML), for a full commentary on the Cadia NTSF embankment slump. A concise, ten-minute technical summary of the slump can also be viewed on the NML YouTube channel (Newcrest Mining Limited, 2019).
Note: This case study has been prepared solely by GDS Instruments following our review and interpretation of a publicly available technical report. This case study has not been reviewed by third parties, and does not constitute technical advice of any sort.