Abstract

This study estimates the fundamental frequency of an 85 m height sand tailings dam in Central Chile using the singlestation Horizontal-to-Vertical H/V Spectral Ratio Method (HVSR), calculated from seismic ambient noise and earthquake records. The dam was constructed by compacting hydraulically deposited sands classified from integral copper tailings, following the downstream construction method. A proper estimate of the dam fundamental frequency is critical for evaluating its seismic response and secure the safe tailings containment when subjected to intense ground motions generated by interface and intraslab earthquakes. Results from the HVSR method are compared with those of the Standard Spectral Ratio method (SSR) calculated as the ratio of the response of the dam crest and that recorded at the dam toe. The fundamental frequency of the dam is about 0.9 Hz in the dam central part away from the abutments, but differences in the vibration frequency are identified along the downstream slope and along the crest axis from the north to south abutment. An analytical relationship between the dam fundamental frequency, the dam height, and the shear wave velocity (Vs) profile is validated.

Abstract

Tailings storage facilities pose an increasingly significant global challenge for mining companies. Given that tailings, the by-products of mine processing plants, demand meticulous management due to the potential hazards associated with storage facility failures, continuous attention is imperative. The repercussions of such incidents can lead to profound and enduring environmental damage in downstream regions. Therefore, consistently monitoring the structural stability of these facilities is paramount to ensure the safety and sustainability of both active mining sites and legacy mines. This paper introduces an innovative approach using muon tomography to analyze the internal density structures of tailings dams. The research, conducted at the BHP Prominent Hill Mine site in South Australia, presents a pioneering method and technology for examining the internal density distribution of tailings storage facilities using muons. Muons, being a natural source of radiation capable of generating X-ray-like scans of large structures, offer a distinctive opportunity to gain insights into the inner structure of tailings storage facilities. Moreover, this technology holds the potential to serve as a foundational platform for future research in the development of early warning systems for detecting structural changes.

Abstract

Recent examples of tailings dam failure remind us how the monitoring of such sites is important. One major factor affecting the stability of tailings storage facilities (TSFs) is the presence and movement of water within the facility. Dam failures are often caused by seepage or the presence of weak layers within the tailings dam or the foundation soil. Thus, monitoring for the presence or movement of water within TSFs is becoming increasingly important, and solutions for permanent, non-intrusive and cost-effective monitoring of dams are a major challenge. One such solution is represented by geophysical imaging techniques such as ambient seismic noise interferometry. Through a research project, a nodal network system of accelerometer sensors was installed in a dense and random array on a TSF embankment wall at an Australian mine. Simultaneously, a fiber optic cable was deployed in a trench at the top of the TSF. Ambient seismic noise was recorded over a few weeks using the nodal network and with the fiber optic cable over several months using Distributed Acoustic Sensing (DAS) technology. Following data acquisition, benchmarking passive seismic imaging from the accelerometer network and the DAS system was conducted to evaluate the DAS capabilities for long-term TSF monitoring.

Abstract

This paper presents the implementation of a Cone Penetration Test (CPT)-based methodology to identify fluid-like tailings in the Tailings Storage Facility (TSF) pond to support a TSF deconstruction. The TSF discussed in this paper was partially raised upstream and classified as very high risk due to its location, next to a creek and a short distance to the downstream community. The owner's preferred mitigation strategy was to proceed with the TSF deconstruction. To inform the deconstruction planning, a comprehensive geotechnical site investigation was conducted, which included CPTu and boreholes with continuous thin wall tube sampling from a floating platform. The investigation identified tailings in the pond as high plasticity clays (CH) with a geotechnical fines content exceeding 95 %. The CPT results indicated low tip resistance, nearly linear pore pressure measurements, and minimal sleeve friction, suggesting the presence of fluid-like tailings in a significant portion of the TSF. The implementation of this methodology allowed to systematically confirm the presence of fluid-like tailings across the pond and define their extent. This information supported the owner’s decision to employ mechanical excavation taking advantage of the tailings flowability. The observations made during the tailings excavation confirmed a good agreement between the CPT assessment and the actual material behaviour. These findings underscore the efficacy of the CPT-based method in guiding safe TSF deconstruction projects

Abstract

Historically, the analyses of tailings storage facilities (TSFs) have primarily focused on understanding the characteristics of tailings, while often overlooking a comprehensive evaluation of the foundation, as seen at Mount Polley in 2014. The Global Industry Standard on Tailings Management (GISTM) Requirement 5.4 stresses the importance of comprehensively addressing all potential failure modes. Numerous platinum TSFs in Southern Africa are underlain by residual clay, specifically a residual mafic rock from the Bushveld Complex. Similar soils, known as "tropical black clay soils", are found in other regions of the world. Surprisingly, there's limited public information on testing and modelling the behaviour of this clay foundation. This paper presents a case study that employs a novel approach to assess the impact of loading from tailings deposition on the underlying clay foundation of an upstream TSF. The analysis investigates how shear behaviour and consolidation characteristics of the clay foundation change with varying TSF heights and construction rates. The approach includes quantifying excess pore water pressures and their influence on the clay foundation's effective stress. The analyses primarily employ traditional limit equilibrium methods to assess TSF stability and foundation behaviour, with the potential to expand to numerical modelling. The study concludes that excess pore water pressures will significantly affect the Factor of Safety (FoS) of a TSF, particularly with adverse consolidation characteristics and increasing TSF height. This is primarily due to the low permeability and changing consolidation coefficient (cv) of the clay layer as the surcharge load increases. Furthermore, the research reveals that, depending on the rate of rise, tailings deposition may induce excess pore water pressures, potentially reducing the FoS. The ability to quantify excess pore water pressures using this novel approach enables a more accurate estimation of the FoS for facilities underlain by low-permeability materials, either residual or transported.