Numerical analysis and geophysical monitoring for stability assessment of the Northwest tailings dam at Westwood Mine

The Westwood Mine aims to reuse the tailings storage facility #1 (TSF #1) for solid waste storage, but, downstream of the Northwest dike is considered critical in terms of stability. This paper uses numerical modeling along with geophysical monitoring for assessing the Northwest dike stability during the restoration phase. The impact of waste rock deposition in the upstream TSF #1 is considered. The geophysical monitoring is based on electrical resistivity methods and was used to investigate the internal structure of the dike embankment in different deposition stages. The numerical simulations were performed with SLOPE/W code. The results show a factor of safety well above the minimum recommended value of 1.5. Geophysical monitoring revealed a vertical variation in the electrical resistivity across the dike, which indicates a multilayer structure of the embankment. Without any current in situ data, the geophysical monitoring helped estimating the nature of the materials used and the internal structure of the embankment. These interpretations were validated by geological observation of geotechnical log of the embankment. Based on this study, it is recommended that the water polishing pond be partly filled before waste rock is deposited in TSF #1. In addition, to ensure the stability of the dike, the piezometric head monitoring prior to and during waste rock deposition is recommended

One-Dimensional Consolidation Parameters Of Cemented Paste Backfills

Each year, mine and mill operations generate enormous amounts oftwo waste types – fine-grained tailings and coarse-grained waste rocks. Fine-grained tailings are either discharged in slurry form to surface tailings dams or delivered in cementitious form to underground mine stopes as backfilling, while coarse-grained rocks are typically stored by depositing as a dry material in large dumps. The engineering design of surface tailings dams or underground mine stopes is often controlled by the high compressibility and low shear strength characteristics of fine-grained tailings. Cemented paste backfill CPB indicating saturated, fine-grained backfills can undergo major consolidation settlement during early curing stages. Thus, a better understanding ofthe rate and magnitude ofboth differential and total settlement ofCPB cured under stress is essential for a proper backfill geotechnical design. The consolidation parameters of CPB can be determined from an improved lab setup called CUAPS (curing under applied pressure system). This setup is capable of simulating the CPB placement and curing conditions, and measuring the consolidation parameters of CPB cured under effective stresses ranging between 0.5 and 400 kPa. In this study, a series of one-dimensional consolidation tests were conducted on CPB samples allowing for examination of the effects of binder type and rate as well as curing time on the compression properties (e.g., coefficient of consolidation cv, compression index Cc, and recompression index Cr) and the final geotechnical index properties (e.g., void ratio ef, water content wf, and degree ofsaturation Sf). Results showed that as the binder content increases, the initial resistance to consolidation increases. The cv value decreases over the course of time due to evolution of the CPB microstructure generated by the hydration process

Development of a 3D analytical solution to evaluate stresses in backfilled vertical openings

RÉSUMÉ: La réponse mécanique du remblai placé dans des ouvertures étroites est largement influencée par son inteaction avec les paroies adjacentes. Les travaux antérieurs portant sur les tranchées et les chantiers remblayés montrent que la théorie de l’effet d’arche peut être utilisée pour estimer la pression dans les ouvertures étroites. Dans cet article, une solution analytique tridimensionnelle est proposée pour évaluer l'état de contraintes dans le remblai le long des parois de l’ouverture. La solution, basée sur une généralisation de l’approche de Marston, est comparée avec des résultats numériques et expérimentaux de laboratoire tirés de la littérature. L’article se termine par une discussion sur certaines caractéristioques et limitations de la solution analytique. ---------- ABSTRACT: The mechanical response of backfill in narrow openings is significantly influenced by its interaction with the surrounding walls. Previous work conduc ted on backfilled trenches and mining stopes indicates that the theory of arching can be used to estimate earth pressures in na rrow, vertical backfilled openings. In this report, a 3D analytical solution is proposed to evaluate the state of stress along the boundaries of the openings. The proposed solution, based on a generalized version of the Marston approach, is compared to numerical modeling and laboratory experimental results taken from the literature. A discussion follows on some particular features and limitations of the analytical solutions

Study of physico-chemical and mechanical characteristics of consolidated and unconsolidated cemented paste backfills

In recent years, it has been observed that the performance and quality of in situ cemented paste backfill (CPB) samples are constantly lower than samples obtained from the same CPB mix poured into laboratory-prepared plastic moulds. This could be well explained by the absence of an efficient laboratory tool capable of mimicking CPB's in situ placement, hardening, and curing conditions relating to stope size and geometry. To meet this need, a new laboratory tool named CUAPS (curing under applied pressure system) was manufactured and used to examine the effect of curing under effective stress on physico-chemical and mechanical properties of CPB, along with plastic mould samples. A comparative study was conducted for both CUAPS and mould samples containing a binder content of 3, 4.5, and 7 wt% after curing times of 7, 14, and 28 days. Results indicate that the performance of CUAPS-consolidated samples are always more realistic than those of plastic mould-unconsolidated samples mainly due to water drainage induced by consolidation. CUAPS has witnessed an advantageous effect on CPB hardening which includes the amount of bleeding water (separation of water from the fresh backfill material) and a combination of drainage of part of the mixing water and the settlement of paste backfill after its placement in the cap

Use of high-density paste bacfill for safe disposal of copper/zinc mine tailings

The safe environmental disposal of sulphide-rich copper/zinc mine tailings is fast becoming a major economic factor in determining the profitability of mining operations. There have been new approaches and better technologies practised in the recent years which allow the mining industries to reduce and/or eliminate the environmental impacts of harmful mine tailings. One of these approaches is the use of high-density paste backfill (HDPB) which is consisting mainly of a mix of solid particles (with the cement) and water, containing between 70% and 85% by dry weight of solids. The increased use of HDPB has improved the reliability, and has reduced the cost of the preparation and transportation systems. This paper focuses on the potential environmental benefits of using the HDPB when tailings are acid generating, and also provides a case study conducted in an underground copper/zinc mine in northeast Turkey in order to illustrate these benefits

Dewatering of Mine Tailings Slurries Using Superabsorbent Polymers (SAPs) Reclaimed from Industrial Reject of Baby Diapers: A Preliminary Study

Traditional deposition of tailings slurry in a tailings storage facility (TSF) can create risks of dike failure. In order to minimize these risks and slurry spillage, the surface deposition technique of densified tailings (DT) through dewatering of the slurry has emerged. The DT technique has the potential to maximize water reuse, improve the shear strength of surface tailings, and reduce the ecological footprint of TSF. The consistency of DT covers a continuum ranging from thickened state, to paste state, to dry state. Despite its efficiency and economic feasibility, DT densification using thickeners sometimes proves unable to achieve the design target solids mass concentration (Cw%). Hence, the use of superabsorbent polymers (SAPs) seems to represent a promising alternative, owing to their higher water absorbent capacity. In this paper, superabsorbent polymers (SAPs) reclaimed from industrial reject of baby diapers (Na-polyacrylates) are explored as a promising alternative to mine tailings slurries dewatering. To this end, laboratory-scale dewatering tests have been performed using two grades of Na-polyacrylate SAPs (grade 1 SAP = SAG-A06P coarse-grained, and grade 2 = SAG-M01P-100 medium-grained) for the tailings slurries densification. A higher water absorbency (or swelling capacity) was observed using the coarser SAPs (SAG-A06P) compared to the finer SAPs (SAG-M01P-100). The preliminary results showed that a SAP volume dosage in the range 10–13 kg of SAP/m3 of slurry allowed achieving a final solids mass concentration (Cw%_final) ≥ 70%, despite the occurrence of gel-blocking phenomenon

Direct shear tests on cemented paste backfill–rock wall and cemented paste backfill–backfill interfaces

This paper presents the results of the shear strength (frictional strength) of cemented paste backfill-cemented paste backfill (CPB-CPB) and cemented paste backfill–rock wall (CPB-rock) interfaces. The frictional behaviors of these interfaces were assessed for the short-term curing times (3 d and 7 d) using a direct shear apparatus RDS-200 from GCTS (Geotechnical Consulting & Testing Systems). The shear (friction) tests were performed at three different constant normal stress levels on flat and smooth interfaces. These tests aimed at understanding the mobilized shear strength at the CPB-rock and CPB-CPB interfaces during and/or after open stope filling (no exposed face). The applied normal stress levels were varied in a range corresponding to the usually measured in-situ horizontal pressures (longitudinal or transverse) developed within paste-filled stopes (uniaxial compressive strength, σc ≤ 150 kPa). Results show that the mobilized shear strength is higher at the CPB-CPB interface than that at the CPB-rock interface. Also, the perfect elastoplastic behaviors observed for the CPB-rock interfaces were not observed for the CPB-CPB interfaces with low cement content which exhibits a strain-hardening behavior. These results are useful to estimate or validate numerical model for pressures determination in cemented backfill stope at short term. The tests were performed on real backfill and granite. The results may help understanding the mechanical behavior of the cemented paste backfill in general and, in particular, analyzing the shear strength at backfill–backfill and backfill-rock interfaces

Gravity-driven 1-D consolidation of cemented paste backfill in 3-m-high columns

This paper investigates and simulates the effect of underground placement conditions of cemented paste backfill (CPB) on the evolution of its physical and mechanical properties. Experimental setups that consist of PVC?MakrolonÒ GP polycarbonate sheet columns, each 3 m high, were built and filled with CPB at two different backfill plants. These setups allow simulating undrained (UD), partial lateral drainage (PLD) and full lateral drainage (FLD) conditions and the measurement of resulting self-weight consolidation settlement of CPB. The results show that maximum drainage water percentages of 15 and 8 % of the CPB total initial water were observed for the FLD and the PLD columns. The results also suggest that in situ backfilled stopes behave in a similar way to that of FLD or PLD conditions

Morphologie et comportement mécanique des discontinuités rocheuses

Not availableLes étapes de cette recherche sont : les essais de cisaillement direct, l'analyse morpho-mécanique et la modélisation. Trois types de joints ont été testés : les joints de granite sablé et bouchardé, et les répliques en mortier d'un joint naturel de schiste rugueux et ondulé. Les essais CNC ont porté sur l'ensemble de ces joints tandis que les essais KNC n'ont porté que sur les répliques. Des relevés topographiques sont effectués à l'aide d'un profilomètre laser avant et après chaque essai de cisaillement. Les résultats des essais ont montré que les raideurs Ks des joints lisses sont plus élevées que celles des joints rugueux. Pour un même joint la raideur Ks selon l'essai KNC est supérieure à la raideur Ks selon l'essai CNC. De nombreux paramètres morphologiques 3D ont été proposés pour caractériser l'anisotropie (degré d'anisotropie ka ; degré d'irrégularité Ir ; degré d'ondularité Sw ; fonction d'anisotropie p(psi)), l'angularité surfacique (inclinaison moyenne qs ; r.m.s. de la dérivée première de la surface Z2s), la rugosité surfacique (rugosité spécifique Srs ; coefficient de tortuosité Ts ; degré de rugosité relative DRr) et quantifier la dégradation des épontes (coefficient de dégradation Wdc ; degré de dégradation Dw). L’analyse morpho-mécanique a montré que la rugosité secondaire joue un rôle dans le frottement des joints bouchardés. Cette analyse a permis de proposer un critère de rupture pour ce type de joints, et qui est exprimé en fonction des paramètres proposés. Le comportement dilatant des répliques du joint de schiste est bien modélisé par les critères de rupture de Ladanyi & Archambault, de Saeb et de Barton. Un essai de classification relative de la morphologie des joints est proposé à partir des paramètres définis. Enfin nous avons proposé des modèles d'évolution de l'état de surface et de l'angle de dilatance au pic en fonction de la contrainte normale. Ces modèles intègrent également la presque totalité des paramètres 3D proposés

New shear strength criteria for rock joints taking into account anisotropy of surface morphology

International audienceThree new peak shear stress criteria were proposed to predict the Variation of shear strength with normal stress for dilatant (irregular and regular surfaces) and non-dilatant to slightly dilatant (planar rough surfaces or regularly undulated surfaces ) rock joints under both constant normal stress (CNS) and constant normal stiffness (CNK) loading. The planar rough surfaces exhibit an isotropic nature whereas the undulated surfaces are anisotropic. These models take into account the progressive degradation of surface roughness during the course of monotonous or cyclic shearing. The third proposed model is a generalized new shear strength criterion which predict successfully the shear strength behaviour of rock joints under CNS and CNK loading