In-pit disposal of mine wastes is a promising alternative management approach to waste rock piles and tailings impoundments. Yet, in-pit disposed wastes are in direct contact with the surrounding rock, and dissolved oxygen or ferric ions from regional groundwater could flow in the waste and contribute to acid mine drainage (AMD) generation. Contaminants contained in the waste pore water could also be dispersed in the environment. Blasting operations results in the creation of new fractures near the pit wall in a zone called the blasted damaged zone (BDZ). These new fractures could provide preferential path around the pit and could affect groundwater and solute fluxes between the backfilled open-pit and the environment. The present study aims to investigate the influence of the BDZ on water and solute exchanges between the pit and the surrounding rock mass. A 3D numerical model was built to simulate a pit backfilled with tailings using PFLOTRAN flow and transport finite volume code on a polyhedral Voronoi mesh. The BDZ was modeled using the equivalent porous media approach. A parametric study was also carried out on the BDZ properties to assess their influence on the water balance. The effect of the BDZ was first assessed by comparing the water fluxes between the open-pit and the environment. Next, the influence of the BDZ thickness, the equivalent permeability at the pit wall and the fracture orientation (BDZ permeability anisotropy) on water fluxes were evaluated. Finally, a solute transport simulation was carried out to analyze the BDZ effect on the solute balance. Main results will be presented and discussed in this paper.

The use of the fully grouted method to install and backfill vibrating wire piezometers has been growing in popularity. Studies have been published with modelling results from finite element seepage analyses under steady state conditions, showing the range of grout/soil permeability ratios under which the fully grouted installation method is considered reliable. Most of the published studies have not examined transient seepage conditions. There is limited published literature with comparisons between the results of field installations using the fully grouted method and the traditional sand pack with bentonite chip seal method. Since much of the published data do not consider situations where transient porewater pressures resulting from application of external stresses (i.e. embankment construction) are induced in a low permeability layer, there remains a large degree of uncertainty about the range of soil and transient seepage conditions under which the fully grouted installation method will provide reliable results.
This paper reports the results of transient finite element analyses of fully grouted installations in low permeability clay layers with adjacent higher permeability soil layers, and provides additional insight into the applicability and limitations of the fully grouted method. The results of several parallel installations using the fully grouted method and the traditional sand pack with bentonite chip seal method are also reported to provide empirical reference cases.

On a complex site where overburden soil stratigraphy is very heterogenous and sensitive to settlement, several structures are planned to be built such as an underground station deep around 40 meters below surface level and associated transit structures allowing passengers to connect with the Express Network Metropolitan (REM) of Montreal, a major project for the collective transport of light rail trains in Montreal and surrounding area. Additional shallower structures such as multi-level car parks and buses facilities are scheduled in the development plan. Authors have assessed the potential damages and risks related to drawdown of groundwater level under pumping operations. This assessment was made for the construction phases (transient state) and for the subsequent operation phase (steady state). In order to support the decision on waterproofing or installing a permanent drainage system for the numerous projected structures avoiding a potential damage risk on existing installations, the team has built a 3D numerical model by collecting data from all the hydrogeological and geotechnical studies carried out on the site since 1959.
This paper presents the different stages of building the numerical 3D model, discuss main parameters that impact the predictive hydrogeological results, describe the evolution of the groundwater flow rate for a construction sequence, compare drawdown of the underground water level following a waterproofing or a drainage decision and expresses monitoring approaches to act mitigating the risk of potential damage.

Dewatering fluid fine tailings (FFT) in centrifuges has recorded large scale success, making it one of the technologies available to operators for tailings processing and improving deposits for reclamation in the oil sands industry. Further densification of tailings in these deposits occur through the natural process of consolidation which will take years to decades; this time factor increases the possibility of time-dependent behavior such as creep and aging effect having an influence on consolidation. This paper reports on experiments carried out to investigate aging effect and consolidation of centrifuge oil sands tailings on a larger scale. These experiments include column dewatering tests, fall cone tests, oedometer tests and modified consolidation test using a steel box with dimensions 0.49m x 0.35m x 0.72m. In order to better assess the centrifuge oil sands tailings dewatering behavior in the steel box, cores were extracted from the steel box; pore water pressure and volumetric water content measurements were taken with sensors inserted at different elevations. Preliminary results will be discussed.

The Iron Ore Company of Canada Carol Lake Mine is located in western Labrador and has been operating since 1962. IOC has three shareholders, Rio Tinto, Mitsubishi Corporation, and Labrador Iron Ore Royalty Company and produces iron concentrate and pellets for sale on the international market.

Geologically, the mine is located in the Sokoman Iron Formation within the Labrador Trough. The orebody has been strongly metamorphosed, deformed, and subjected to variable supergene (limonitic) alteration resulting in a complex hydrogeologic setting. The hydrostratigraphy of the orebody is broadly divided into two hydrogeologic domains. Domain 1 is the largest and consists of un-weathered iron formation and associated rocks. Rock within this domain is relatively non-porous / non-permeable and the hydrogeology is dominated by complex fracture networks. Domain 2 consists of zones of weathered limonitic rock propagated to depth along faults. Rock within this domain is generally porous / permeable, is internally well connected, with high hydraulic conductivity values observed throughout.

Identifying productive dewatering wells, even with a broad understanding of the hydrostratigraphy, is challenging at IOC due to the complex geology. The stakes are high, as the drilling and construction of deep dewatering wells is both a time consuming and expensive endeavor. A dry well represents millions of dollars of lost investment and even higher additional future costs due to the absence of effective advanced dewatering infrastructure. For the cost of a diamond drill hole, which regardless of the intended outcome has inherent geological and geotechnical value, the risk to the business can be mitigated. This paper will examine how diamond drilling has been utilized to increase confidence in well targets and improve the success rate of drilling campaigns. Discussion is focused on the conceptualization and performance of currently operating wells at IOC and their positive impact on the operation.

Large strain consolidation behaviour of mineral slurries regulates the performance of tailings management and reclamation plans. Hydraulic conductivity-void ratio relationship especially influences this behaviour, dominating the long-term performance of fine-grained slurries with higher initial water contents. However, determination of this function can be very challenging and time-consuming, considering the long durations of consolidations test and large variation in hydraulic conductivity with void ratio. A laboratory test column study was conducted to evaluate the consolidation behaviour of diluted Leda clay and thickened gold tailings . The test column was instrumented with tensiometers and Enviroscan (capacitance-based) sensors to determine the pore water pressures and volumetric water changes respectively. Also, a robotic arm was connected the sensors for more detailed profiling. The collected data is then utilized to estimate hydraulic conductivity of the tested materials using Instantaneous Profiling Method (IPM). Finally, the measured data and the predicted behaviour of the material is compared using a large strain consolidation software, UNSATCON, to tease out non-consolidation behaviours such as creep.