Qian Gu, Joshua Chan
Tailings Storage Facilities (TSF) constructed using upstream methods may have static liquefaction risks due to the strain softening behaviour of contractive tailings. Conventional Limit Equilibrium Analyses (LEA) using either peak strength or residual strength fail to address the stress-strain compatibilities between materials at different stages of softening or hardening, resulting in over or underestimating embankment stabilities. Static numerical analyses (Finite Element or Difference) are unable to identify the threshold stability due to their inability to converge close to or beyond equilibrium conditions.
In this study the failure triggering process is modelled with dynamic Finite Element Analyses (FEA) with the stress-softening behaviour of contractive tailings simulated by Norsand Model. The embankment failures are identified by either non-zero residual velocities along downstream face, or a drop in average shear stress along potential failure surfaces under increasing disturbing surface pressure. Threshold disturbing surface pressure estimated using these two methods are in close agreements. Factor of Safety (FoS) values estimated from peak mobilised shear strength are found to be between those estimated using the peak and residual shear strength in LEA. q-p’ stress paths in tailings clearly show the stress ratio increasing towards and beyond instability ratio during undrained triggering process. The developments of zones of shear softening and p’ reduction with increasing undrained disturbances help visualise the failure triggering process.
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Neeta Arora, Prashant Agrawal, Yogendra Deva, Ravi Kumar
The tectono-lithologic complexities and the accompanying extreme mass wasting processes make the Himalaya a difficult terrain for river valley development projects envisaging dams and other diversion structures. Besides exceptionally thick riverbed deposits leading to management of deep foundations, abutting the dams often poses challenges in view of difficult ground conditions. The paper looks at three scenarios where the presence of highly decomposed strata, slumped mass and unconsolidated riverbed material led to serious problems in abutting the dams and invariably delayed the project completion. The design approach to special abutment issues is discussed in the light of investigations, explorations, laboratory and field tests, etc. In conclusion, while dependable engineering geological mapping and assessment is considered the backbone, innovative investigations and engineering play crucial role in successful implementation of projects.
Ryan Singh, Jiri Herza, James Thorp
Recent and continual failures of tailings storage facilities (TSFs), often resulting in catastrophic consequences, has led to calls for action from the industry, stakeholders and the public at large. Several standards and guidelines are being prepared at the time of writing, most notably a Global Industry Standard on Tailings Management (GISTM), with the overall objective to reduce the rate of TSF failures globally. While better guidelines are certainly necessary, there are requirements that must be carefully followed in developing a document that has the ambition to become a standard. If such requirements are not fulfilled, the document can become ineffective or potentially have the opposite result to that which was intended. This paper discusses whether or not the GISTM meets the requirements of the standards and analyses the potentially negative impacts of its implementation on the industry and wider society. Based on this analysis, this paper provides several recommendations for improvements that should be considered by the GISTM panel and other working groups preparing standards and guidelines.
Mark Pearse, John Pisaniello, Sam Banzi, Peter Hill
A completely new dam safety regulation framework was introduced into NSW in November 2019. The new framework addresses all aspects of dam safety management. The implications for dam owners in respect of risk reduction measures (RRMs) that will need to be undertaken have been the matter of debate and are the focus of this paper. The Dams Safety Regulation 2019 requires that dam owners eliminate or reduce the risk posed by their dams but “only so far as is reasonably practicable” (SFAIRP). This is a change from the previous Dams Safety Committee requirement that risks should be reduced as low as reasonably practicable (ALARP). The previous guidance around the extent and timing of risk reduction has been removed and dam owners are now required to determine what is ‘reasonably practicable’. These changes were anticipated to save hundreds of millions of dollars from the reduced cost of risk reduction measures across the state of NSW. These savings appear unlikely to materialise given that dam owners are likely to be highly cognisant of the need to meet the common law expectation that RRMs should be implemented unless the costs associated with the RRMs are grossly disproportionate to the benefits gained. The key changes in the new regulatory framework are identified along with the legal and financial implications in regard to RRMs followed by next steps that should be considered by dam owners in NSW. Many of the implications are applicable to other dam owners who operate under common law (including all states of Australia and New Zealand).
Matthias WILD, James STEWART, Chris IRVIN, Sander Van Ameijde
The awareness of safe and sustainable utilisation of all forms of construction such as bridges, tunnels, dams or industrial buildings during its whole lifetime is increasing more and more. The safe operation of our dams is of critical importance to society. As our assets age, the focus on monitoring, control systems and lifespan management is of increasing importance. Communities need to have peace of mind these assets are not going to fail. To prevent failures of structures, a common method is for periodical or situational site visits to check the crucial points of construction. Site visits are cost intensive, subjective and non-continuous. This results in a global research focus on measurement devices and evaluation systems to generate a full structural health monitoring system which guarantees measurement and data evaluation adapted for the specific application over the full lifespan.
For important structures like the Hinkley Point nuclear power plant or Australian Dam structures it’s not just the inspection costs and a sustainably utilisation during service life that are important. The safety during operation of the nuclear power plant is also critical to its operation. To monitor the deep excavation at the power plant DYWIDAG provided geotechnical systems combined with measurement sensors and a monitoring concept for the lifespan of the structure. About 14,000 soil nails and bar anchors are stabilising the excavation. Movements of the retaining wall will lead to a change of stress in the geotechnical tension members. This change is monitored by DYNA-Force Sensors, which are used for load monitoring. This monitoring system has been used successfully in a range of critical structures like stadium roof-beams, staycables, dam-anchors with strands or bars.
A simple installation and read out of sensors is not a major facilitation compared to site visits. The implementation of sensors in a sophisticated monitoring system is the big advantage of structural health monitoring which guarantees a safe and sustainable utilisation of the construction. DYWIDAG is making infrastructure lifespan management smarter and offers a cloud-based online sensor management system (Platform Interactive) which enables processing of large volumes of sensor data and performing complex calculations. It provides real-time alerting, presenting the information in an innovative and interactive way, removing subjective interpretation and providing numerical data online in real time. Platform Interactive with plug and play pre-configured sensors, may also be adapted and applied for a range of SHM projects. It provides continuous reporting and the reassurance structures are performing as they should without the possibility of failure. At DYWIDAG we are making infrastructure lifespan management smarter, safer, stronger
Gideon Steyl, Ralph Holding, Lis Boczek
A Monte Carlo method for assessing liner systems is applied with outcomes demonstrating the range of discharge that could occur over the liner interface. The Monte Carlo approach allows for variation of fill material over the liner system and includes the assessment of a second compacted zone either above or below the liner zone. In this paper clay liners were evaluated due to regulatory guidelines and it could be demonstrated that similar performance to a 1 m clay liner could be attained using compacted material to reduce discharge over the liner interface. The approach applied in this paper allows for at least a worst-case quantification of seepage risk which could be included in liner selection criteria or presenting liner options to regulators.