Method of Reducing Risk to Mine Tailings Dams by Controlling Melting Rate of Snow

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Canadian Application No. 3190234, filed on Feb. 17, 2023 entitled “METHOD OF REDUCING RISK TO MINE TAILINGS DAMS BY CONTROLLING MELTING RATE OF SNOW” and whose entire disclosure is incorporated by reference herein.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to a field of snow management practices in mine tailings storage facilities to reduce the risks associated with snowmelt. More particularly, the present disclosure relates to a method of reducing risk to tailings dams structure by the control of snowmelt rate and reducing meltwater flow rates in snow tailings storage facilities.

BACKGROUND OF THE DISCLOSURE

The subject matter discussed in this background section should not be assumed to be prior art merely as a result of its mention herein. Similarly, any problems mentioned in this background section or associated with the subject matter of this background section should not be assumed to have been previously recognized in the prior art.

Exploitation of mineral resources generates large amount of solid wastes such as tailings, which are produced as a result of the processes used to extract economically important minerals from an ore (Bussiere and Guitonny, 2020). Various waste management strategies are used for storing tailings. However, tailings are most commonly stored over large surface areas known as tailings storage facilities (TSFs). These TSFs often use tailings dams as retaining structures for the unsaturated wastes and designed to withstand more than the critical loads of tailings anticipated during operation.

Despite recent technological developments in the design of TSFs, geotechnical instability and failure of TSFs remains a common problem (Rico et al., 2008; Azam and Li, 2010; Caldwell, 2017). While the reasons for these failures are complex, inadequate water management is usually a common factor (Rico et al., 2008; Strachan and Goodwin, 2015). Therefore, a proper design and implementation of effective water management infrastructure are crucial considerations in the construction of a TSF.

The most common water management infrastructure in TSFs are spillways, flumes, and ditches, which are used to channel process waters and meteoric water to surface water storage and treatment sites (Vick, 1990; Blight, 2010). The design of water management, storage, and treatment facilities, as well as their operating conditions, is based on anticipated seasonal variations in surface water flow and the cumulative effects of water level control facilities on flow (Environment Canada, 2009). For mine sites located in colder regions, the seasonal accumulation and melting of snow represents a recurring, albeit sometimes unpredictable factor in water management. This is further complicated by climate change. Because TSFs generally have large footprints, the accumulation of snow on their surface during winter can be significant and comprise a large component of the annual water inventory. In these areas, spring snowmelt often brings the greatest peak flow rates, thus placing potentially extreme demands on the capacity of water management infrastructure and posing risks to tailings dams, flumes, and treatment capacity. Therefore, it is essential to develop strategies for mine operators to better control excess water flows from the melting snow and reduce the geotechnical and environmental risks associated with snowmelt. Therefore, there is a need for a method to control the melting rate of the snow in TSFs.

SUMMARY OF THE DISCLOSURE

The following terms used herein are defined as follows:

- “snowmelt rate” is defined as the melting rate of snow over time.
- “meltwater” is defined as water resulting from melted snow.
- “snow management pile” may be used interchangeably with “engineered snow pile”.

The present disclosure provides, in one alternative, a method of mitigating impacts of snowmelt by the management of winter water inventory with the use of snow management piles (SMPs).

The present disclosure further provides, in another alternative, a method of monitoring snow and water management.

The present disclosure further provides, in one alternative, a method for controlling snowmelt rate of snow and delaying or slowing down the snowmelt rate, and to control the melting of snow in a tailings storage facility area thereby extending the rate of snowmelt over a period of time and reducing water outflows due to melting snow over a period of time. In particular, in one alternative, there is provided a method for i) reducing failure of tailing dam structures due to the uncontrolled melting of snow adding water outflow pressure and volume to the tailing dam structures, and ii) reducing extra space needed for storing snow, thereby increasing the safety of the tailing dam structure, reducing a negative impact on the environment and achieving cost savings.

In one alternative, there is provided snow piles in a tailings storage facility comprising i) preparing one or more snow piles, in one or more shapes, in a storage area of a tailings storage facility, by collecting and piling snow in said storage area of said tailings storage facility. In one alternative, said collecting and piling of said snow comprises the use of snow collecting machines. In one alternative, said one or more shapes may include conic shape, cubic shape, ridge shape and combinations thereof. In one alternative, said snow collecting machines may include, but not limited to, low ground pressure snow grooming equipment, crawler dozers, wheel loaders and combinations thereof. The storage area of a tailings storage facility comprises one or more tailing dam structures to prevent the flow of meltwater in a restricted area. Further, there is provided monitoring a rate of snowmelt of the one or more snow piles via sensor systems. Further, the sensor systems that may be used include, but are not limited to, light detection and ranging (LiDAR) sensor and structure from motion (SfM) photogrammetry. The one or more engineered shapes of the one or more snow piles is configured to reshape the accumulated snow at the surfaces of TSFs and remoulding and densifying the snow into the one or more engineered shapes to control snowmelt rates, reduce meltwater flows and prolong the duration of spring runoff.

In one alternative, said engineered snow pile has an angular slope value greater than 1 and a height value greater than the length of the base of the engineered snow pile and a predefined density greater than the density of naturally accumulated snow on the ground surface.

In another alternative, said engineered snow pile further comprises a cover overtop said engineered snow pile. In one alternative, said cover comprises a synthetic cover on a surface of said engineered snow pile creating a barrier to reduce, preferably prevent, contact of said engineered snow pile with outside environment. In one alternative, the synthetic cover is made from a material selected from the group consisting of polyurethane and polyethylene. In another alternative, the synthetic cover is foldable and reusable. Further, in yet another alternative, the synthetic cover further comprises an insulating material.

In another alternative, said method further comprises covering the one or more snow management piles with a cover, in one alternative, a synthetic cover, on a surface of said engineered snow pile creating a barrier to reduce, preferably prevent, contact of said engineered snow pile with outside environment. In one alternative, the synthetic cover is made from a material selected from the group consisting of polyurethane and polyethylene. In another alternative, the synthetic cover is foldable and reusable. Further, in another alternative, the synthetic cover further comprises an insulating material.

According to one aspect, there is provided a method of controlling at least one of i) snowmelt rate and ii) meltwater flow, in a storage area of a tailings storage facility, the method comprising steps of:

- preparing at least one snow management pile in said storage area by collecting snow in one or more shapes selected from the group consisting of cubic, conical and ridge-shape;
- wherein the one or more shapes of the one or more snow piles having an angular slope reducing, preferably minimizing, sun exposure of a surface of said one or more snow piles; and
- wherein the one or more shapes of the one or more snow piles having a density and height configured to reduce at least one of i) said snowmelt rate and ii) said meltwater flow in said storage area of said tailings storage facility.

In one alternative, said angular slope is greater than 1.

In one alternative, said density is greater than density of naturally accumulated snow.

In one alternative, said height is greater in length than a length of a base of said snow management pile.

In one alternative, the at least one snow management pile in the storage area is formed by using snow grooming equipment.

In one alternative, the snow grooming equipment pushes the snow towards the storage area and shapes the collected snow into a desired shape.

In one alternative, the at least one or more shapes is conical.

In one alternative, the at least one snow management pile further comprises a cover reducing contact of the at least one snow management pile with the outside environment.

In one alternative, the cover comprises a synthetic cover.

In one alternative, the synthetic cover further comprises an insulating material.

In one alternative, the synthetic cover is foldable and reusable.

In one alternative, the synthetic cover comprises a flexible material.

According to another aspect, there is provided a engineered snow pile in a storage area of a tailings storage facility, said engineered snow pile controlling at least one of i) snowmelt rate and ii) meltwater flow in said storage area of said tailings storage facility, said engineered snow pile comprising:

- a predetermined density greater than a density of naturally accumulated snow;
- an angular slope reducing, preferably minimizing sun exposure of a surface of said engineered snow pile;
- a shape selected from the group consisting of cubic, conical and ridge-shaped; and
- a height greater in length than a length of a base of said engineered snow pile.

In one alternative, the angular slope is greater than 1.

In one alternative, said shape is conical.

In one alternative, the engineered snow pile further comprises a cover reducing, preferably minimizing contact of the engineered snow pile with the outside environment.

In one alternative, said cover is a synthetic cover.

In one alternative, the synthetic cover further comprises an insulating material.

In one alternative, said cover is foldable and reusable.

In one alternative, said cover is flexible.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various alternatives of systems and methods of various aspects of the disclosure. Any person of ordinary skill in the art will appreciate that the illustrated element boundaries (e.g., boxes, groups of boxes, or other shapes) in the figures represent one example of the various boundaries representative of the disclosure. It may be that in some examples one element may be designed as multiple elements or that multiple elements may be designed as one element. In other examples, an element shown as an internal component of one element may be implemented as an external component in another and vice versa. Furthermore, elements may not be drawn to scale. Non-limiting and non-exhaustive descriptions of the present disclosure are described with reference to the following drawings. The components in the figures are not necessarily to scale, emphasis instead being placed upon the illustrated principles.

Various alternatives will hereinafter be described in accordance with the appended drawings, which are provided to illustrate and not to limit the scope of the disclosure in any manner, wherein similar designations denote similar elements, and in which:

FIG. 1 illustrates a snow management pile in a conic shape for a tailing storage facility (TSF) and a vehicle to facilitate the formation of the snow management pile, according to an alternative of the present disclosure;

FIG. 2 illustrates a flowchart of a method of controlling snowmelt rate of a snow management pile, according to an alternative of the present disclosure;

FIG. 3 is a table representing temperature, precipitation, and thickness of average snow measurements, according to an alternative of the present disclosure;

FIG. 4A illustrates an aerial view of initial footprints, cleared surface and various snow management piles, according to an alternative of the present disclosure;

FIG. 4B depicts construction of the snow management piles, according to an alternative of the present disclosure;

FIG. 4C depicts constructing the conic snow management pile, according to an alternative of the present disclosure;

FIG. 4D depicts a profile of the final cubic snow management pile, according to an alternative of the present disclosure;

FIG. 4E depicts the cross section of the snow management piles, according to an alternative of the present disclosure.

FIG. 5 is a table representing final configurations and shape properties of the conic, cubic and ridge-shaped snow management piles, according to an alternative of the present disclosure;

FIG. 6 is a table representing survey parameters using a light detection and ranging (LIDAR) system and a structure from motion (SfM) hotogrammetry, according to an alternative of the present disclosure;

FIG. 7A is a chart of daily climatic parameters recorded at the ECCC Val d'Or weather station, according to an alternative of the present disclosure;

FIG. 7B is a chart of the comparison of the snow on the ground recorded at the ECCC Val d'Or weather station with in situ measurements and LiDAR surveys, according to an alternative of the present disclosure;

FIG. 8A illustrates a three-dimensional (3D) point cloud obtained by the LiDAR sensor, according to an alternative of the present disclosure;

FIG. 8B illustrates SfM photogrammetry data, according to an alternative of the present disclosure;

FIG. 8C illustrates areas of sun exposed surfaces based on LiDAR acquisitions, according to an alternative of the present disclosure;

FIG. 8D illustrates camera positioning and aerial triangulation points used to generate the SfM photogrammetry reconstruction of the snow management piles, according to an alternative of the present disclosure;

FIGS. 9A-9C illustrate charts showing volume, height and footprint of the ridge, cubic and conic snow management piles throughout a monitoring period as determined by the LiDAR sensor and the SfM photogrammetry, according to an alternative of the present disclosure;

FIG. 10A illustrates a chart showing in situ snow specific gravity as a function of elevation from a snow management pile tailings interface, according to an alternative of the present disclosure;

FIG. 10B illustrates the snow, liquid water, and ice system developed within a snow management pile, according to an alternative of the present disclosure;

FIGS. 11A-11C illustrate charts showing evolution of the fraction of initial snow on ground and air temperature and evolution of the fraction of an initial snow management pile volume, height and footprint throughout a monitoring period, according to an alternative of the present disclosure; and

FIGS. 12A-12B illustrate charts showing an estimate average meltwater flow and melted snow of snow on ground compared to snow management piles of various shapes, as a function of the degree-days between two consecutive surveys, according to an alternative of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

The following detailed description of various alternatives, as represented in the figures, is not intended to limit the scope of the present disclosure but is merely representative of various alternatives. While various aspects of the alternatives are presented in drawings, the drawings are not necessarily drawn to scale unless specifically indicated.

Some alternatives of this disclosure, illustrating all its features, will now be discussed in detail. The words “comprising,” “having,” “containing,” and “including,” and other forms thereof, are intended to be equivalent in meaning and be open-ended in that an item or items following any one of these words is not meant to be an exhaustive listing of such item or items or meant to be limited to only the listed item or items.

It must also be noted that as used herein and in the appended claims, the singular forms “a,” “an,” and “the” include plural references unless the context dictates otherwise. Although any systems and methods similar or equivalent to those described herein can be used in the practice or testing of alternatives of the present disclosure, the preferred systems, and methods are now described.

Alternatives of the present disclosure will be described more fully hereinafter with reference to the accompanying drawings in which like numerals represent like elements throughout the several figures, and in which example alternatives are shown. Alternatives of the present disclosure may, however, be embodied in alternative forms and should not be construed as being limited to the alternatives set forth herein. The examples set forth herein are non-limiting examples and are merely examples among other possible examples.

Referring now to FIG. 1, there is illustrated a snow management pile (SMP) 100 for a tailing storage facility (TSF), according to an alternative of the present disclosure.

Although various waste management strategies exist, tailings are most commonly stored at the surface in large areas known as tailings storage facilities (TSFs). These TSFs often use tailings dams as retaining structures for the unsaturated wastes and must be able to withstand more than the critical loads anticipated during operation and after closure. During the winter season, the ground surface of the TSF gets covered with snow from snow fall. The snow fall forms a thick layer on the ground surface covering a large surface area which results in reduction in storage capacity of the TSF.

For mine sites located in colder regions, the seasonal accumulation and melting of snow represents a recurring, albeit sometimes unpredictable factor in water management. Because TSFs generally have large footprints, the accumulation of snow on their surface during winter can be significant and comprise a large component of the annual water inventory. In these areas, spring snowmelt often brings the greatest peak flow rates, thus placing potentially extreme demands on the capacity of water management infrastructure and posing risks to tailings dams, flumes, and treatment capacity. Therefore, to reduce the risk, one or more snow management piles 100 are formed at the TSF, as shown in FIG. 1. The one or more snow management piles 100 may be defined as an engineered managed pile of snow over a concentrated surface area. Said managed pile of snow may vary in size, shape, and surface area covered by the pile. Thus, the present disclosure focuses on reducing the surface area covered by snow in a TSF and reducing the rate of snowmelt by formation of snow management piles. In one alternative, the one or more snow management piles 100 may be a cone-shaped or conical snow management pile (SMP), a cube-shaped or cubical SMP, or a ridge-shaped SMP.

In one alternative, the one or more snow management piles 100 may be constructed in a conic-shape. In one alternative, the snow management pile angle of slope is selected to reduce the snowmelt rate of the one or more snow management piles 100. As the angle of slope of the one or more snow management piles 100 increases, the angle of the side of the one or more snow management piles to exposure to the sun is impacted and further slowing down the snowmelt rate. The height of the one or more snow management piles also affects the snowmelt rate. The greater the height of the one or more snow management piles, the slower the snowmelt rate.

Referring now to FIG. 2, a flowchart of a method 200 of controlling snowmelt rate of snow by the application of the one or more snow management piles 100, is provided, according to an alternative of the present disclosure. FIG. 2 is herein described in conjunction with FIGS. 3-12B.

At first, one or more snow piles are prepared in a storage area by collecting snow in one or more shapes via snow collecting machines, at step 202. In one alternative, the one or more snow piles may be formed by pre-compacting the snow accumulated in a selected area of the TSFs. The one or more shapes include conical, cubic, ridge shapes and combinations thereof. The one or more snow piles may be constructed sequentially in multiple layers to form the final structure. In one alternative, low ground pressure snow grooming equipment may be employed to construct a base of the one or more snow management piles. The base of the one or more snow piles may be an initial structure. Further, the rest of the one or more snow management piles structure may be formed by a wheel loader to construct different shapes and a desired defined slope of a surface of the one or more snow management piles.

It may be noted that temperature and precipitation measurements of the storage area may be retrieved while preparing the one or more snow management piles. Further, the thickness of fallen snow on the ground surface of the TSF may also be measured. For example, daily temperature and precipitation readings are taken from an Environment and Climate Change Canada (ECCC) weather station proximate the TSF. One example is found in FIG. 3, table 300, for the period spanning February 25 to May 27, due to the station's proximity to the mine TSF.

Further, the thickness of the snow cover may vary significantly within even small areas, the daily thickness of snow on the ground recorded at the ECCC weather station data is compared to manual, on-site measurements. Such approach validates the representativeness of snow thickness measurements at the ECCC weather station.

Example 1—Snow Management Piles at an Existing Mine

Three pilot-scale SMPs with different geometries (conic, cubic and ridge-shaped) were constructed at the TSF of the mine in Quebec. The SMPs were monitored for snowmelt rate and meltwater production over the period of February-April.

The effectiveness of the SMPs at controlling snowmelt was evaluated by analyzing the changes in volume, height and footprint of the SMPs over time. Meltwater flow rates were also estimated by correlating the evolution of volume change with snow density.

FIG. 4A illustrates an aerial view 400 of initial footprints, cleared surface and several snow management piles. The snow management piles may be constructed in at least three configurations in the TSF. The at least three configurations include a ridge-shaped snow management pile 402, conic-shaped snow management pile 404 and a cubic-shaped snow management pile 406. In one alternative, the one or more snow management piles may be oriented along an east-west axis. Thus, the south face of the one or more snow management piles may be oriented perpendicular to the direct action of the sun throughout the day, and in particular, at noon.

As best seen in FIG. 4E, there is depicted a cross section of the ridge-shaped snow management pile 402, the conic-shaped snow management pile 404 with a cover 408, and the cubic-shaped snow management pile 406.

The snow management piles were constructed at a TSF of a mine, in this example, the mine in Quebec.

Further, construction of the one or more snow management piles were initiated in mid-February by pre-compacting the snow accumulated on the selected area of the TSF. The one or more snow management piles were further constructed at the beginning of March using two Caterpillar 938H wheel loaders, a Caterpillar D6N LGP crawler dozer, and a Caterpillar 320E hydraulic excavator equipped with a long reach boom-stick. A total of about 12,000 m²of snow was cleared to construct the one or more ridge-shaped snow management pile 402, the one or more conic-shaped snow management pile 404 and the one or more cubic-shaped snow management pile 406. Considering that the thickness of the snow on the ground is approximately 70 centimeters (cm) at the time of construction in March, this resulted in a groomed volume of about 8,400 m³of snow.

Further, the one or more ridge-shaped snow management piles 402 and the one or more cubic-shaped snow management piles 406 were constructed in single lifts using the wheel loader and the crawler dozer (as shown in FIG. 4B). The crawler dozer was used to clear and push the snow towards the one or more snow management piles 100, and the wheel loaders were used to groom and shape the one or more snow management piles into the desired shapes. The maximum height of the one or more snow management piles in this example was limited by the height of the hinge pin of the wheel loader's bucket (in this example the value was 3.8 meters for the Caterpillar 938H. The final height of the ridge-shaped snow management pile 402 and the cubic-shaped snow management pile 406 after snow grooming was 3.5 meters as shown in FIG. 1. Further, the construction of the conic-shaped snow management pile 404 was performed in two layers. A first layer was constructed with the crawler dozer and the wheel loaders in a process similar to that used for the ridge-shaped snow management pile 402 and the cubic-shaped snow management pile 406. Further, a long reach boom-stick hydraulic excavator was used to construct a second layer and shape of the conic-shaped snow management pile 404, as shown in FIG. 4(c).

In this example, the final height of the conic-shaped snow management pile 404 was 7.3 meters. The final configurations and shape properties of the snow management piles, are shown in table 500 in FIG. 5. Table 500 shows the initial footprints of the conic-shaped snow management pile 404, the cubic-shaped snow management pile 406 and the ridge-shaped snow management pile 402 as 665 m², 965 m², and 1150 m². In this example, the ridge-shaped snow management pile 402 contained more snow than the cubic-shaped snow management pile 406 or the conic-shaped snow management pile 404. Although the conic-shaped snow management pile 404 contained the least amount of snow of the snow management piles of this example, the conic-shaped snow management pile 404 was twice the height of the other snow management piles. Following the construction and during monitoring of the snow management piles, the snowfall that accumulated around the snow management piles were occasionally cleared.

The rate of snowmelt of the snow management piles were monitored via sensor systems, at optional step 204, and the snowmelt is controlled at 206.

The sensor systems included a light detection and ranging (LiDAR) sensor, and a structure from motion (SfM) photogrammetry sensor. The effectiveness of the snow management piles at reduce snow melting rates and delaying of the snowmelt period were assessed through periodic measurements of the volume of snow contained in each of the snow management piles. The volume of the snow management piles were measured eighteen times between March and May through an aerial LiDAR sensor and the SfM photogrammetry surveys acquired using an unmanned aerial vehicle (UAV). The UAV used was a DJI Matrice 300 RTK equipped with a DJI Zenmuse L1 Livox Lidar module installed in a single, downward gimbal configuration. The Matrice 300 RTK was ideal for monitoring due to its i) self-heating batteries, which allow the UAV to operate at temperatures as low as −20° C., as well as its ii) high wind-resistance (15 m/s), which helped to minimize the no-fly wind conditions.

The Zenmuse L1 LiDAR sensor has a high-precision inertial measurement unit (IMU), a ranging accuracy of 3 cm at 100 m, and is capable to support up to three returns. Further, the Zenmuse L1 LiDAR sensor may also be installed with a Red Blue Green (RGB) mechanical shutter and 1-inch complementary metal oxide semiconductor (CMOS) camera that is suitable for photogrammetry surveys. The UAV was linked to a DJI D-RTK 2 Mobile Station, which was used as a base station to provide real-time kinematic (RTK) position corrections during the acquisitions. With this configuration, RTK positioning accuracy was approximately 1 cm horizontally and 1.5 cm vertically. All Lidar and SfM photogrammetry surveys in this example were pre-programmed and flown using the automatic survey functions. The inertial measurement unit (IMU) was also calibrated before each flight. The mapped area was about 98,000-99,000 m²and flight speed and distance were optimized to reduce the total acquisition time, as shown at table 600 in FIG. 6. Table 600 shows a summary of flight, LiDAR sensor and the SfM photogrammetry survey parameters.

In this example, the flight altitude was set to 50 meters (m) to obtain high resolution acquisitions. This yielded to a point cloud density of 787 pts/m²and a ground sampling distance (GSD) of 1.26 cm/pixel. The LiDAR scans were acquired at a 70% lateral overlap and using a three-return repetitive scanning pattern (70.4° horizontal and 4.5° vertical field of view) at a rate of 160 kHz. RGB photos were also obtained for point cloud colouring. SfM photogrammetry surveys were performed using 80% and 70% lateral and frontal overlaps, respectively. Five surveyed ground control points (GCPs) were used to validate geo-referencing and assess survey accuracy. All surveys were done on sunny to partly cloudy days at approximately the same time.

Further, three-dimensional reconstructions and data analysis were done with DJI Terra Pro (v3.4.4). This software uses Compute Unified Device Architecture (CUDA)-based reconstruction algorithms. Reconstructions were performed in a standalone configuration on a computer equipped with an Intel Core i9-10900 CPU, NVIDIA Geforce RTX 3070 GPU, and 64 GB RAM. Reconstructions were performed at the highest resolution. Volume calculations were performed using the mean plane of the surface of the TSF as reference for both LiDAR and SfM photogrammetry analyses.

A detailed characterization of the snow contained in the ridge-shaped snow management pile 402 was carried out between March 11 and May 12. This characterization primarily assessed changes in snow density associated with snowmelt within the ridge-shaped snow management pile 402. Forty samples of snow were taken from different depths (surface to the snow management pile tailings interface) using a large (100×15 cm), custom Adirondack-type snow sampler. Twelve other samples of snow were taken from undisturbed ground around the TSF for comparison. The snow sampler consisted of a reinforced PVC pipe that was equipped with a tooth cutter at the base and allowed for the recovery of samples ranging in length from 15 to 55 cm. The mass of each snow sample was weighed using a portable electronic scale. The results of the snow characterizations were used to provide an estimate of meltwater flow rates generated from the snow management piles, which were compared to those of the undisturbed snow samples.

Data from the ECCC Val d'Or weather station showed that air temperature gradually increased from −30 in late February to 30° C. by May. However, temperatures remained close to 0° C. during most of March and April as shown in FIG. 7A at 700. Further, FIG. 7B compares the evolution of snow thickness over time as reported by the ECCC weather station to values obtained manually and by LiDAR surveys. All methods yielded similar values for snow thickness. Therefore, the ECCC curve for the snow on the ground was considered representative of site conditions. Snow melt occurred primarily between mid-March and late April and rain-on-snow events occurred several times during snowmelt. The rapid decrease in snow on ground during the first two weeks of April suggests that the peak flows associated with snowmelt occurred during this period.

FIGS. 8A-8B show examples of 3D point clouds and reconstructions obtained by the LIDAR (FIG. 8A) and SfM photogrammetry (FIG. 8B) with the position of the camera shown to evaluate the volume, height, and footprint of the snow management piles. FIGS. 8A-8B are described in conjunction with FIGS. 9A-9C.

The aerial view 800 or a three-dimensional (3D) point cloud results show that the absolute volume obtained for each snow management pile at any given time point varied slightly depending on the measurement method, as shown in FIG. 9A at 900. Volumes measured by LiDAR sensor were generally greater than those computed using the SfM photogrammetry. Further, comparisons between the surveyed GCPs and the geo-referenced LiDAR sensor and SfM photogrammetry generated point clouds (3D point cloud) indicated absolute horizontal and vertical accuracies of 2 to 5 cm, suggesting that the surveys and reconstructions were accurate enough to be comparable. Therefore, any difference in the LiDAR sensor and the SfM photogrammetry volume measurements may be due to limitations in the abilities of the LIDAR sensor and the SfM photogrammetry to capture and represent all the features and snow conditions associated with snowmelt.

FIG. 8D shows that the density of aerial triangulation points used to generate the SfM photogrammetry reconstructions were good both close to and on the snow management piles.

The difference in volume calculations between the LiDAR sensor and the SfM photogrammetry were more important for the ridge-shaped snow management pile 402 and the cubic-shaped snow management pile 406 than for the conic-shaped snow management pile 404, due to shape and surface effects. In this example, the ridge-shaped snow management pile 402 and the cubic-shaped snow management pile 406 showed an average difference of 17% between the two measurements methods, whereas the conic-shaped snow management pile 404 showed a 13% mean difference.

FIGS. 9A-9C illustrate that the ridge-shaped snow management pile 402 and the cubic-shaped snow management pile 406 contained more snow than the conic-shaped snow management pile 404. The average initial snow volumes of the ridge-shaped snow management pile 402, the cubic-shaped snow management pile 406, and the conic-shaped snow management pile 404 were 2565 m³, 2275 m³, and 1355 m³, respectively. Over the snowmelt period, the absolute volume of the ridge-shaped snow management pile 402 and the cubic-shaped snow management pile 406 decreased more rapidly than that of the conic-shaped snow management pile 404. The conic-shaped snow management pile 404 stayed higher than the ridge-shaped snow management pile 402 and the cubic-shaped snow management pile 406 throughout the monitoring period. In contrast, the ridge-shaped snow management pile 402 and the cubic-shaped snow management pile 406 maintained a greater footprint than the conic-shaped snow management pile 404 for most of the monitoring period. Snowmelt ended on May 18 for both the ridge-shaped snow management pile 402 and the cubic-shaped snow management pile 406 and was extended by a further 11 days in the conic-shaped snow management pile 404, with thawing ending on May 28. With respect to the natural accumulation of snow on the TSF, the snowmelt period was extended by approximately four weeks using the ridge-shaped snow management pile 402 and the cubic-shaped snow management pile 406 and nearly six weeks using the conic-shaped snow management pile 404. These results demonstrate that the tested snow management piles are effective at extending the snowmelt.

The snow that accumulated naturally at the surface of the TSF prior to the construction of the snow management piles had an average in situ density (ρ) of 267 kg/m3 with little if any significant change throughout most of the monitoring period. The average density gradually reached 730 kg/m3 during the last two weeks of April. At that time, there was less than 10 cm of snow still on the ground. Density measurements performed on the ridge-shaped snow management pile showed two distinct density profiles during snowmelt. FIG. 10A provides a chart 1000 showing in situ snow specific gravity as a function of elevation from the snow management piles-tailings interface. After construction and during early to mid-spring, the density within the one or more snow piles were relatively homogeneous. The density measured during the months of March and April ranged from 411 kg/m³to 536 kg/m³and most measurements were close to the average value of 490 kg/m³. During this period, no significant quantity of liquid water was observed within the snow management piles. Considering the initial volumes of snow contained in the snow management piles, as shown in FIG. 9A, and the average snow density in early spring, the ridge-shaped snow management pile 402, the cubic-shaped snow management pile 406 and the conic-shaped snow management pile 404 contained approximately 1257 m³, 1115 m³, and 664 m³of water, respectively.

Snow, ice, and liquid water multi-phase flow regime developed within the snow management piles, as spring progressed. Meltwater and meteoric water migrated towards the base of the snow management piles which resulted in a denser and layered distribution of snow density within the snow management piles. During this time, there was a 10- to 20-cm-thick layer of ice that accumulated at the snow management piles-tailings interface (ρ=910 kg/m³). This layer of ice was overlain by a 10-cm-thick capillary fringe that has an average density of 850 kg/m³. The density then gradually decreased as elevation increased, reaching an average of 610 kg/m³for elevations ≥45 cm. This depth profile is depicted visually as shown in FIG. 10B.

The monitored size parameters (volume, height, and footprint) were converted to fractions of their initial values, as shown in 1100 of FIGS. 11A-11C, to better compare the snow management piles effectiveness at controlling snowmelt. FIG. 11A shows that the volumetric decreases in all the snow management piles followed similar trends. The peak flow associated with snowmelt of the undisturbed ground occurred roughly during the first two weeks of April, despite air temperatures remaining very close to 0° C. During this period, the rate of thaw (represented by the steep slope of the change in thickness of the snow on the ground as a function of time) was elevated and significant quantities of water were released. In the undisturbed snow, melting finished on approximately April 22. In contrast, on the same date, more than half of the snow contained in each snow management pile remained frozen.

Further, a second, but attenuated peak in flow was observed from the last week of April to the second week of May in association with snowmelt from the snow management piles. These results suggest that most of the meltwater associated with the undisturbed ground may be managed before the peak flow associated with the snow management piles. This has an influence on the meltwater peak flow and can contribute to reducing the load on water management and treatment facilities as well as geotechnical infrastructures. Snow management piles may also help operators reduce the need for excessive storage and treatment capacities associated with extreme events.

The snow management pile ability to mitigate meltwater flow was examined by using the snow management pile volume and snow density measurements to roughly estimate the average flow of water released from the one or more snow piles as a function of the number of degree-days between two consecutive surveys. FIG. 12A at 1200 shows water flow (m³/m²/day) normalized to the area of snow (m²) cleared for each of the snow management piles. This allowed for a comparison of the water flow generated by the snow management piles with that of the undisturbed ground for a similar surface area. Results show that the tested snow management piles generally maintain meltwater flow rates below 0.01 m³/m²/day, while one third of the meltwater flow rates are ≥0.015 m³/m²/day for the undisturbed ground. Estimated average water flows on the order of 0.015 m³/m²/day were sporadically observed in the snow management piles. However, these flows were calculated for temperatures four-fold higher. Broadly, these results also suggest that the snow management piles provide a significant dampening effect on meltwater flow rates. Periods with high degree-days do not drastically increase the meltwater flow. Climate change is increasing the frequency and intensity of extreme climatic events, which significantly influence many variables associated with the water balance. Therefore, the dampening effect of the snow management piles on meltwater flow rates is particularly relevant in the context of climate change since it can be difficult to accurately predict the evolution of climatic conditions.

Further, the investigation on the effect of size and shape the average amount of melted snow (in m³) per m²of snow management piles footprint per day was calculated and plotted as a function of the degree-days between two consecutive surveys, as shown in FIG. 12B. The amount of snow melted per m²of the snow management piles footprint was similar among the tested three shaped snow management piles. Further, results also show that, despite having a volume nearly 50% smaller than the ridge-shaped snow management pile 402 and the cubic-shaped snow management pile 406, the conic-shaped snow management pile 404 took longer to thaw. Proportionally, the decrease in height of the conic-shaped snow management pile 404 was slower than the ridge-shaped snow management pile 402 and the cubic-shaped snow management pile 406, as shown in FIG. 12B. Conversely, the footprint of the conic-shaped snow management pile 404 decreased more rapidly than the ridge-shaped snow management pile 402 and the cubic-shaped snow management pile 406.

Thus, the rate of melting of snow may be controlled by arranging and forming snow management piles, in one alternative, in an array, inside a TSF of a tailings dam. The angular slope and height of the snow management pile are configured to minimize the rate of melting of the snow management piles.

In an alternative, each of the ridge-shaped snow management pile 402, the conic-shaped snow management pile 404 and the cubic-shaped snow management pile 406 may be oriented in an array inside a tailings dam. For example, the ridge-shaped snow management pile 402, the conic-shaped snow management pile 404 and the cubic-shaped snow management pile 406 may be further constructed in a manner to face towards the north east side of the storage area in order to further minimize the melting rate of the snow. Further the snow management pile may be arranged in a conic-shaped snow management pile 404.

Further, the ridge-shaped snow management pile 402 and the cubic-shaped snow management pile 406 extended the snowmelt period by approximately four weeks, whereas the conic-shaped snow management pile 404 extended snowmelt by nearly six weeks, with respect to unmanaged snow. Calculations suggest that most of the meltwater associated with the undisturbed ground may be managed before the peak flow associated with the one or more snow management piles 100 and provide a significant dampening effect on meltwater flow rates.

Further, the results demonstrate that the snow management piles 100 may be effective at extending snowmelt, mitigating meltwater flow, and reducing environmental and geotechnical risks associated with rapid snowmelt. The snow management piles may help mine operators reduce the need for excess storage and treatment capacities associated with extreme events.

In one alternative, the snow management pile 100 may further comprise a cover, in one alternative a synthetic cover, creating a barrier to prevent contact of the surface with the outside environment. In one alternative, the synthetic cover may be fabricated with flexible material to cover the snow management pile.

In the foregoing description, certain terms have been used for brevity, clarity, and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such words are used for description purposes herein and are intended to be broadly construed. Moreover, the alternatives of the apparatus illustrated and described herein are by way of example, and the scope of the disclosure is not limited to the exact details of construction.

While the above description contains many specificities, these should not be construed as limitations on the scope, but rather as an exemplification of one alternative thereof. It should be understood that the broadest scope of this disclosure includes modifications such as diverse shapes, sizes, and materials. Accordingly, the scope of the present disclosure should be determined, not by the alternatives illustrated, but by the appended claims and their legal equivalents.

While there is shown and described herein certain specific structures embodying various alternatives of the disclosure, it will be manifest to those skilled in the art that various modifications and rearrangements of the parts may be made without departing from the spirit and scope of the underlying inventive concept and that the same is not limited to the particular forms herein shown and described except insofar as indicated by the scope of the appended claims.

It may be appreciated by one skilled in the art that additional alternatives may be contemplated. These and other advantages of the mechanism of the present disclosure will be apparent to those skilled in the art.

Method of Reducing Risk to Mine Tailings Dams by Controlling Melting Rate of Snow

Information

Publication Number

Date Filed

Date Published

Inventors

CPC

International Classifications

Abstract

Description

Claims

Priority Claims (1)