Documents published in Scipedia

• Comparative Liquefaction Triggering Assessment of Gravelly Reclamations using the CPT, DPT, and Shear-Wave Velocity

  R. Dhakal*, M. Cubrinovski

  ISC2024.

  
  

  Abstract

  Major challenges are encountered in characterizing and performing liquefaction assessment of gravelly soils since performing traditional in-situ tests, such as the Cone Penetration Test (CPT), in gravelly soils can be challenging, and since gravelly soils are not well-represented in existing case history databases used to develop semi-empirical methods for liquefaction assessment. This has been the primary reason for the ongoing efforts to develop methods based on other invasive tests, such as shear-wave velocity (Vs), and penetration tests with larger probes and greater energy delivered to the rod, such as the Dynamic Cone Penetration Test (DPT). While CPT-based liquefaction analyses have been comprehensively studied, limited research has been conducted comparatively evaluating the performance of the other two methods. This paper performs liquefaction triggering assessment of gravelly reclamations using data from the welldocumented case history of the port of Wellington (New Zealand) using CPT, DPT, and Vs measurements. Results show that while the Vs measurements overestimate liquefaction resistance, the DPT and CPT agreed relatively well with observations from past earthquakes due to the greater sensitivity of these test methods to soil density and stratigraphy

  Abstract
  Major challenges are encountered in characterizing and performing liquefaction assessment of gravelly soils since performing traditional in-situ tests, such as the Cone Penetration [...]

  • 0
  •  read

• On-site characterization of compacted iron ore tailings-Portland cement blends for dry stacking systems

  J. de Sousa Sailva*, H. Mansur Chaves, H. Scheuermann Filho, N. Consoli

  ISC2024.

  
  

  Abstract

  Dry stacking of filtered tailings has become feasible due to the development of novel dewatering technologies. It offers an alternative to address the safety-related issues associated with conventional slurry disposal in reservoirs confined by upstream heightened dams. The operation and maintenance of such structures are challenging because of the high degree of uncertainty inherent in this material due to its spatial variability in state and gradation. It is also susceptible to liquefaction when saturated and in a loose state. In contrast, the filtered tailings can be compacted and piled up to hundreds of meters to meet prescribed design requirements. Eventually, a cementing agent can be incorporated into the tailings before compaction to enhance the general engineering properties. Nevertheless, few dry-stack facilities operate; none use cement as a stabilising agent. Accordingly, this paper assesses the mechanical response of artificially cemented iron ore tailings compacted in the field to form an experimental pile. Plate load tests and cone penetration tests were used. The experimental pile was divided into four sections, each compacted with different combinations of roller passes (4 or 6 passes) with and without vibration frequency. The results showed that the compacted material was practically insensitive to variations in compaction parameters, as evidenced by similar results in the tested sections' stress-strain responses and cone tip strength values. This study also highlights the effectiveness of field testing in investigating the response of stacking plants and the importance of using a small amount of cement to achieve adequate mechanical performance.

  Abstract
  Dry stacking of filtered tailings has become feasible due to the development of novel dewatering technologies. It offers an alternative to address the safety-related issues [...]

  • 0
  •  read

• Drying and wetting cycles in tailings dams: effects on physical, mechanical and hydraulic properties

  R. Rodriguez-Pacheco, J. Butlanska*, A. Onel Oliva, A. Muñoz-Moreno

  ISC2024.

  
  

  Abstract

  The study examines the drying and wetting cycles of tailings dams (TDs) and their impact on physical, mechanical and hydraulic properties. TDs are divided in four zones: the dike, the discharge zone, the transition zone and the distal zone (also known as the decantation pond). The filling process of the tailings dam involves five phases: 1) dumping and wetting, (2) segregation, (3) sedimentation, (4) consolidation, and (5) drying. The occurrence of drying and wetting cycles depends on the water balance, which can be expressed as Inflow = Outflow ± Storage Coefficient. These cycles are influenced by factors such as changes in the discharge point within TD dike and reservoir, weather conditions, and other external factors. The analysis of drying and wetting cycles in TDs reveals several trends: (a) grain size, density, internal friction angle, and permeability decrease from the discharge zone toward the decantation pond and (b) porosity, fine particle content (particle less than 75 microns), plasticity, cohesion, and capillarity height increase as we move toward the decanting lagoon. Despite these findings, there is currently no established methodology for managing the filling process or controlling wetting and drying cycles of TDs.

  Abstract
  The study examines the drying and wetting cycles of tailings dams (TDs) and their impact on physical, mechanical and hydraulic properties. TDs are divided in four zones: the [...]

  • 0
  •  read

• Integrated characterisation of bentonite pellet structures for in situ test installation

  J. Torres-Serra*, A. Mesa-Alcantara, E. Romero

  ISC2024.

  
  

  Abstract

  Bentonite pellet-based mixtures are currently investigated as candidate materials in large-scale in situ sealing experiments such as the Vertical SEALing project by the Institute for Radiological protection and Nuclear Safety (IRSN, France) due to their expected gap-filling capacity in engineered barrier systems for the geological disposal of radioactive waste. In the short term, after installation, the hydro-mechanical behaviour of these pellet-based structures is governed by pellet-pellet interactions, which have been characterised experimentally by oedometer compression tests and numerically by discreteelement modelling of single-layered pellet skeleton samples. In this work, we integrate these experimental and numerical tools to characterise the compressibility of three-layered pellet-based structures with axis-oriented arrangements. We validate the simulated deformation of bentonite pellet samples against experimental data and analyse the evolution of the dry density distribution and axial stiffness along the oedometer compression curve. Our integrated approach has implications for the emplacement and monitoring in situ tests on multi-layered pellet-based barrier systems.

  Abstract
  Bentonite pellet-based mixtures are currently investigated as candidate materials in large-scale in situ sealing experiments such as the Vertical SEALing project by the Institute [...]

  • 0
  •  read

• Characterization of residual soil in tailings dam foundations: A combined analysis of in-situ tests and geophysical surveys with emphasis on method correspondence

  J. Oliveira Barbosa, J. Paulo Souza Silva*, B. Guimaraes Delgado, P. Pazzoto Cacciari

  ISC2024.

  
  

  Abstract

  New legislation in Brazil requires that all upstream tailings dams must be closed. However, understanding the characteristics of the foundation and deposits of these dams can be complex, and conventional investigations may not be sufficient. Geophysical methods can complement conventional approaches and provide a better understanding of geotechnical structures. The objective of this investigation is to comprehensively characterize residual soil from a tailings dam foundation by integrating data from direct and indirect approaches. Data from CPTu, SCPTu, SPT, geophysical profiles, and MASW were analyzed. The results were compared with empirical correlations for other soil types, and it was found that the equations are not effective to represent the materials. The study discusses the advantages and limitations of using these empirical equations.

  Abstract
  New legislation in Brazil requires that all upstream tailings dams must be closed. However, understanding the characteristics of the foundation and deposits of these dams [...]

  • 0
  •  read

• Development of a 3D ground model to design the stabilisation of a downstream dam founded on weak and liquefiable units

  J. Rola, M. Sottile, N. Rivas, L. Roldan*, A. Sfriso

  ISC2024.

  
  

  Abstract

  Athree-dimensional (3D) ground model was developed to design the stabilisation of a dam founded on both weak and liquefiable units up to about 18 m below ground surface. The ground model covers a linear extent of approximately 800 m and was developed from five separate site investigations completed over a four-year period and digitisation/georeferencing of historic drawings/plans. Combined, the investigation comprised 206 cone penetration tests (CPTs), 37 boreholes and 36 test pits, including several vane shear tests, ball penetrometer tests and sampling. CPT data was processed to identify different material behaviours, generally based on the following features: corrected tip resistance; sleeve friction resistance; pore water pressure ratio; state parameter; and the soil behaviour type index. Each CPT interpretation was compared with information from the nearest borehole using a purpose-built python code. This information was reviewed manually in an iterative process to delineate the various geotechnical unit based on CPT response and the physical logs. This process identified a continuous weak organic layer across the site which had not been previously picked-up by the Engineer of Record (EoR). The works identified nine separate geotechnical units, with one of these subdividable based on its CPT response/grain size. The 3D ground model was built in Seequent Leapfrog Geo using the following information: unit levels specified from each CPT, digitised historic drawings/plans and a topographic survey. This paper describes the process of development and presents the full 3D ground model used as critical input to the stabilisation design of the dam

  Abstract
  Athree-dimensional (3D) ground model was developed to design the stabilisation of a dam founded on both weak and liquefiable units up to about 18 m below ground surface. The [...]

  • 0
  •  read

• Evaluation of the susceptibility to flow liquefaction of an iron ore tailings using the state parameter and Yield Stress Ratio approach

  A. Faria, M. Junior*, J. Carneiro, M. Dias, G. Pinto

  ISC2024.

  
  

  Abstract

  Flow liquefaction is observed in saturated or nearly saturated geomaterials, showing a strain-softening response during undrained shear, primarily in very loose sands and silts, as well as in very sensitive clays. The Cone Penetration Test (CPTu) has been gaining popularity among the geotechnical community to evaluate the state of a soil profile due to its good repeatability, detailed information on the soil stratigraphy and extensive detailed scientific studies to guide the application of the test results. Susceptibility to flow liquefaction is typically evaluated by estimating the in-situ state parameter (𝜓) since it directly correlates to the soil behaviour at large strain, as shown by Jefferies & Been (2016). Mayne & Sharp (2019) suggested using the yield-stress-ratio (YSR = σp’/σv0’) to estimate the soil state using a threshold of YSR ≈ 3. Currently, in the Brazilian Mining Industry, it is common to find the application of different approaches to evaluating the susceptibility of mining tailings to flow liquefaction (e.g., Plewes et al., 1992; Olson, 2001; Shuttle & Cunning, 2008; Robertson, 2016). This paper presents an evaluation of the susceptibility of an iron ore tailings (IOTs) to flow liquefaction using the following recently published approaches: i) Mayne and Sharp (2019), using the yield stress ratio (YSR) approach; ii) Smith et al. (2021), using a generalised CPTu state parameter inversion method based on the NorSand Widget; and iii) Robertson (2022), with the updated Kc. The main results show a good convergence between the three methodologies used.

  Abstract
  Flow liquefaction is observed in saturated or nearly saturated geomaterials, showing a strain-softening response during undrained shear, primarily in very loose sands and [...]

  • 0
  •  read

• Difficulties in Building a Ground Model When Lacking Historic Data Archives and its Impact in TSF Safety Assessment

  I. Lopes*, M. Garcia, G. Tavares

  ISC2024.

  
  

  Abstract

  Sometimes, when working in TSF safety analysis, the historic archives with the original ground topography or details about the TSF design and construction are few or inexistent. The knowledge of the bedrock position, as the details about the embankment construction are essential to know, for instance, the tailings thickness and the construction type. For the analysis of TSF current state stability the ground/structure model is essential, and is, in many cases, very difficult to define with few and low-quality data. The original ground topography is, often, obtained from aerophotogrammetric reconstruction, from satellite images or aerial photos, originally with low resolution and uncertainty of more than 10 m for the elevation. In this paper is presented a case-study from a TSF where the initial data package had only the feasibility design and some very simplified reports that checked the stability of the dam before an upstream raising, i.e. it didn’t exist much information and the details about the site and about the structure were very limited. To “add” difficulties to the process of defining the bedrock surface and to establish the TSF design, the embankments were built with local rocks (mainly schist and phyllite), and during the initial analysis of historical satellite images it was noticed that the original ground was excavated in different areas to increase storage area and obtain construction materials. This paper presents the steps developed to establish the definition of the bedrock ground surface and the difficulties felt and its impacts on TSF safety assessment are discussed.

  Abstract
  Sometimes, when working in TSF safety analysis, the historic archives with the original ground topography or details about the TSF design and construction are few or inexistent. [...]

  • 0
  •  read

• CPTu for Assessment of Flow Liquefaction of Tailings with Similar Physical Characteristics

  C. Lebron*, M. Pio dos Santos Junior, A. Viana Da Fonseca

  ISC2024.

  
  

  Abstract

  A geotechnical assessment of mine tailings state conditions using the static cone penetration test performed at different tailings storage facilities (TSF’s) will be presented in this paper. Both tailings evaluated herein are deposited as a slurry (hydraulic deposition) and have similar grain-size distribution curves. A set of Cone Penetration Tests (CPTu) with pore pressure measurements were performed at each site to evaluate the state of the tailings. To assess the contractive-dilative behavior classical methodologies were adopted such as i) the contractive/dilative boundary suggested by Robertson (2016) ii) the approach suggested by Plewes et al. (1992) and cited by Jefferies and Been (2016) and iii) the yield stress ratio method proposed by Mayne and Sharp (2019). Partial drainage effects will be identified with classical methodologies. The results were compared to evaluate the difference and limitations of each methodology. Comments on the similarity between the two tailings evaluated herein will also be presented to explain the differences in behavior due to aspects such as mineralogy, gradation, stress history and deposition.

  Abstract
  A geotechnical assessment of mine tailings state conditions using the static cone penetration test performed at different tailings storage facilities (TSF’s) will be presented [...]

  • 0
  •  read

• Geotechnical Parameters of Filtered Tailings and Waste Rock from the Itabira Complex used in Stacking Projects

  D. Eloi*, M. Paganin, D. Bastos, W. Maciel, M. Filho, R. Silva

  ISC2024.

  
  

  Abstract

  The complex where we used the materials ins this study, explores iron ore in an open pit process and is formed by a significant number of mines, and all their geotechnical structures such as waste rock stackings, tailings dams and, recently, the stackings that are being constructed with waste rock and tailings. For the piles formed by the shared disposal of waste rocks and filtered tailings, the characterization of the materials and the strength and critical state parameters determined the executive methodology and the safety factors required for the projects. The waste rocks and filtered tailings are mechanically disposed and divided into zones defined not only according to the geotechnical characteristics of the materials, but also the structural and operational needs of the stacking, which are divided into the confining zone and the confined zone. In the confining zone, compacted waste is deposited. The aim of this procedure is to enhance the structural performance by employing materials with higher resistance. In the confining zone, as closer to the outer layer of the pile, greater shear strength is mobilized. In the confined zone, friable waste, and mining tailings are disposed. In this zone, there is less mobilization of shear strength. For tailings, control and evaluation adhere to parameters outlined by the Critical State Line, employing the void ratio control of layers. This ensures dilatant mechanical behaviours for all confinement stresses specified in the project.

  Abstract
  The complex where we used the materials ins this study, explores iron ore in an open pit process and is formed by a significant number of mines, and all their geotechnical [...]

  • 0
  •  read