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Bituminous geomembranes (BGM) for ponds in mining

February 1st, 2021 / By: / Feature

By Natalie Daly and Bernard Breul 

FIGURE 1 RUSAL Alumina clarifier pond bituminous geomembrane (BGM) liner, Ireland

Bitumen has emerged as a standard 20th-century waterproofing material in civil and water engineering in the form of bituminous concrete, asphalt and bituminous geomembranes. The first applications of bituminous geomembranes (BGM) were in France in 1975 near Grenoble and for potable water storage reservoirs at a 6,562-foot (2,000-m) altitude in the Alps.

General presentation of BGM

The structure of BGM is multilayered, including a nonwoven polyester geotextile at the core, which provides mechanical resistance and high puncture resistance. This geotextile is impregnated in an elastomeric bitumen compound that provides the waterproofing properties and ensures the product’s longevity by impregnating the geotextile. The glass fleece, also impregnated in the bitumen, provides the dimensional stability during fabrication. The sand coating improves the resistance to ultraviolet (UV) light and grip, and the antiroot film prevents puncturing from roots and vegetation (Figure 2).

FIGURE 2 Typical structure of a BGM

Manufacturing is done under strict quality-control procedures certified under an ISO 9002 quality-assurance scheme and under a French and European ASQUAL certification, and it is CE marked (European marked). The factory, located in the north of France, operates with an ISO 14001 environmental certification.

Some technical characteristics of BGM giving advantages for a use in pond projects include: 

Low permeability of 6 × 10-14 m/sec (ASTM E96).

High mass per unit area between 124 and 189 ounces per square yard (4.2 and 6.4 kg/m2), giving an important resistance to lifting in windy regions and possible installation even in windy regions at high altitudes (ASTM D3776).

The density is 68 pounds per cubic foot (1.2 ton/m3), so BGM can be installed underwater without floatation. The seams underwater are welded with a mastic (ASTM D1505 and ASTM D792, Method A).

High puncture resistance for static puncture following ASTM D4833 is between 101 and 146 pound-force (450 and 650 kN), puncture by aggregates NF P84510 between 4.5 and 7.9 pound-force (20 and 35 kN) and hydrostatic puncture resistance ASTM D5147 between 72.7 and 81.8 psi (501 and 564 kPa) for the range of 0.16 and 0.19 inch (4.0 and 4.8 mm) of thickness and XP P84523 between 152 and 218 psi (1,050 and 1,500 kPa) for the range between 0.14 and 0.19 inch (3.5 and 4.8 mm) of thickness on a bedding with grain size of 1–2 inches (25–50 mm). With this property, tire-mounted vehicles and equipment can drive on top of the geomembrane during installation and maintenance (Figure 3).

FIGURE 3 Tire-mounted equipment traffic directly on top of BGM

BGM has a very low thermal expansion coefficient following ASTM D1204 and is 100 times lower than high-density polyethylene (HDPE). This means there are no wrinkles with thermal and temperature variations. Therefore, there is no fatigue phenomenon, and it is possible for welding and covering of the geomembrane at any time during the day and the year, without interruption.

The sand surfacing reinforces the UV resistance of the bitumen. This face has a friction angle of 34° and up, depending on the material placed on top. This value is following ASTM D5321 tests done by Sageos (Quebec, Canada) and the Institut National des Sciences Appliquées de Lyon (INSA) (Lyon, France).

BGM can store potable water, conferring to the American international certification of NSF/ANSI 61.

BGM has a high resistance to earthquakes, as demonstrated in the field. The Milpo Dam in the Chincha region of Peru is lined with BGM and had undergone an earthquake of a magnitude of 8.1 on the Richter scale. Laboratory testing was followed to verify the integrity of the geomembrane by Precision Laboratory in California for the Los Angeles Department of Water and Power (LADWP). The lab found no damage to the integrity of the liner.

Easy to seal to rock and concrete structures, thus allowing the same permeability at any point of the lining (Figures 4a, 4b and 4c).

FIGURE 4a: Concrete pipe
FIGURE 4b: Rock
FIGURE 4c: Concrete lining

The manufacturer supplies personnel to train local teams of installers on-site.

BGM in shale gas ponds examples

The use of BGM in tailings ponds built in very cold temperatures and harsh weather conditions allows for an extension of the installation period during the freezing months (i.e., –49°F [–45°C] in February in Siberia at the Kinross Kupol Gold Mine), which provides a quicker return on investment by not delaying the installation time.

In the Northwest Territories of Canada, the Diavik Diamond Mine is located on a 7.7-square-mile (20-km2) island in Lac de Gras, 186 miles (300 km) northeast of Yellowknife. The mine is owned by a subsidiary of Rio Tinto and Aber Diamond Limited Partnership. Average minimum and maximum daily temperatures are around –13°F (–25°C), and precipitation exists in different forms of drizzle, rain, hail, sleet and snow. The processed kimberlite containment (PKC) retention pond was initially completed with an HDPE geomembrane, but owners and the consultant Golder Associates Vancouver were looking to improve the quality and reduce the cost of the PKC pond and other ponds. By avoiding contamination of the purity of the water of Lac de Gras, BGM was able to present a more economical solution by offering a larger period of installation and welding that can tie into 5,250 feet (1,600 m) of existing HDPE. The extension to the existing pond was to be an additional height of 16 feet (5 m). Installation was completed by a company based in Yellowknife that specializes in geomembrane installation in cold weather conditions, and it has appreciated BGM’s flexibility even when stored and unrolled at –40°F (–40°C). No special precautions inside tunnels to protect from the cold were required during welding, which was performed in the open air at –13°F (–25°C). This means the installation and welding of BGM is largely independent of temperature and weather conditions (Eldridge and Harman 2006). 

For the installer, working with BGM was the same at –13°F (–25°C) as it would have been at 68°F (20°C). The geomembrane maintained its flexibility and was as easy to install and weld at both temperatures. Even when it snowed, the installation of the geomembrane continued as usual. BGM can thus be installed at any time of the year. For the initial HDPE solution, the grain size for the bedding and cover material was specified a 2-inch minus (50-mm minus). Tests carried out on-site showed that a 6-inch minus (150-mm minus) material could be used for bedding and a 15.7-inch minus (400-mm minus) could be used for cover without damage to the BGM. The 6-inch minus (150-mm minus) bedding material was compacted and the surface was then raked by hand to remove the larger particles protruding above the surface, as is typically performed on every worksite (Figure 5). The cover material was then dumped along the crest and pushed by a track loader, down the slope over the geomembrane. The use of relatively coarse bedding cover materials and cushion materials as well as the elimination of the need for a protective geotextile (not recommended in regions that have a lot of wind) under and above the geomembrane reduced the total cost of construction. Only one geosynthetic (BGM) was needed, which saved on cost for material layers and installation time in an extreme weather region (Elliott 2007).

FIGURE 5 Welding high-density polyethylene (HDPE) geomembrane/BGM

In Finland, the Kiitilä Mine lies within the Arctic climatic region. Temperatures are cold, with an average mean monthly temperature in July of 59°F (15°C) and in January of 5°F (–15°C). The mean annual air temperature at the site is 32°F (0°C). The mine facility plan called for a small and a large pond, for a total initial area of 133 acres (54 ha) (today, more than 247 acres [100 ha]) to receive the processed water from the gold-processing plant. Water from the ponds then recirculates back to the process, which makes the water circulation a closed system. As part of the environmental permit for the mine, a watertight liner was required and BGM was accepted by the Finnish Ministry of the Environment (Figure 6) (Huru, Palolahti and Breul 2008). 

FIGURE 6 BGM installation at Kiitilä Mine in Finland

The design of the ponds called for an excavation surrounded by dikes to get the required volume. The cross section of the dam consists of a core built with blasted rock with particle size up to 2 feet (600 mm) in diameter. The upstream side of the dike was covered with a layer of blasted rock but with a maximum diameter of 1 foot (300 mm) and protected by a layer of gravel not exceeding 2.2 inches (55 mm) in diameter. This last layer was compacted using an excavator equipped with a compacting plate to provide a smooth surface with no ruts. The dikes were designed to function like a zoned dam built with material recovered from the mining operation. A 3.3-foot (1-m) thick sealing layer was then placed on the bottom of the pond, which consists of the excavated moraine rolled and compacted, exhibiting a saturated hydraulic conductivity less than 5 × 10-8 m/s. BGM has a low thermal expansion coefficient, so there are no wrinkles throughout the day when temperatures vary. With this characteristic, the geomembrane lies flat on the ground and provides, in combination with the low-permeability moraine, a permanent and durable double layer of watertightness. The project was initially designed with a polymeric geomembrane (HDPE or linear low-density polyethylene [LLDPE]), but the client expressed interest in switching to a bituminous geomembrane to line the ponds at the Kiitilä Mine for the mentioned economic reasons and because BGM can be installed at temperatures as low as 5°F (–15°C), which was a critical element with respect to the schedule in the northern region, since the construction was anticipated to extend until October, the most moist and humid period of the year. A local contractor did the installation with an output of 86,111 square feet (8,000 m2) per day after on-site training by a manufacturer monitor. The total surface area of BGM covered is 30 million square feet (2.5 million m²). 

In Russia, the Kinross Kupol Gold Mine is in the northwestern part of the Anadyr foothills in the Chukotka Autonomous Okrug, which has site access by helicopter or fixed-wing aircraft. Every winter a 249-mile (400-km) ice road is constructed from the northern port of Pevek to the site; it is used to transport goods to the site. The Kinross Kupol Gold Mine requires a tailings dam to store tailings produced by the milling process. The Kinross Kupol tailings impoundment is formed by a rockfill dam that utilizes an upstream-facing BGM liner to minimize seepage through the structure. A deep cutoff trench to anchor the liner at the base in front of the dam over frozen ground was used to minimize the potential seepage through the dam foundation. To ensure permafrost was retained in the foundation, the foundation preparation, liner placement and covering were carried out from January through March and late October through December, when ambient temperatures were often near –40°F (–40°C). Installation of the liner was carried out through all seasons. Every extension of the rockfill dam from 2006 until today is watertight with a BGM of 0.2-inch (5.1-mm) thickness (Figure 7).

FIGURE 7 Cold weather installation at the Kinross Kupol Gold Mine in Russia

BGM has advantages not only in cold weather conditions but also in hot weather conditions. It is effective in temperatures ranging from –49°F to 194°F (–45°C to 90°C). 

In Ireland, RUSAL Alumina is a large bauxite processing plant based in the southwestern part of the country. The clarifier pond had been badly leaking for quite a while due to inadequate performance of the existing HDPE geomembrane, which must store high-temperature liquid at 194°F (90°C). BGM uses a special bitumen compound with a temperature of penetration, which measures the penetration of a needle (test NFT 666004 or BS 200: Part 49), of 266°F (130°C). To meet the plant’s waste license requirements by the Environmental Protection Agency of Ireland, RUSAL Alumina decided to upgrade the lining of the clarifier pond by installing BGM. The overall scope involved the site setup and the removal and disposal of existing semisolid wastes. The final elements of the project involved pouring a 6-inch (150-mm) deep asphalt concrete slab over the entire base for regular maintenance cleaning works (Figure 8).

FIGURE 8 Concrete passageway to spill the process water directly from the Rusal Alumina factory at 194°F (90°C) to the clarifier pond, Ireland

A shale gas project in Queensland, Australia, required a high resistance to heat for the installation and storage of water between 158°F and 194°F (70°C and 90°C). The embankment of this large process water pond belongs to the Queensland Gas Corp. and needed remediation, because the clay in the embankment was dispersive and was eroding. The pond required 1.05 miles (1.7 km) of embankment to be remediated and covered to prevent future erosion. The main considerations in choosing a liner for this application were the liner’s ability to resist wind uplift and wind-generating waves, as well as the ruggedness of the site.

The heaviest BGM with a mass of 1.23 psi (6 kg/m2) was selected to prevent wind erosion generated by waves on the dam embankment. The ruggedness and puncture resistance of the BGM means that rocks could be placed directly on top of the liner at the base of the slope, preventing uplift of the liner. The liner was placed into an anchor trench at the top of the slope and installed at an ambient air temperature of 102˚F (39˚C) (Figure 9).

FIGURE 9 Process water pond remediation in Queensland, Australia

Conclusion

BGM has been used successfully for more than 40 years in hydraulics and environmental protection applications. BGM possesses high physical and mechanical properties, allowing it to remain exposed. Its installation is straightforward, using propane-torch welding, and its high unit weight allows it to be installed in rough weather conditions with local installers trained by the manufacturer on-site, with no wrinkling due to temperature variations. Subgrade preparation for this liner is reduced to the minimum, and there is no need for geotextile cushion layers. Finally, maintenance is easy and can be performed by an on‐site maintenance team. 

The BGM applications mentioned in this paper were done to the satisfaction of international consultants and owners (public and private) on time and without delays due to bad weather, low temperatures or strong winds.

References

ASTM D1204. Standard Test Method for Linear Dimensional Changes of Nonrigid Thermoplastic Sheeting or Film at Elevated Temperature, American Society for Testing and Materials, West Conshohocken, Pa.

ASTM D1505. Standard Test Method for Density of Plastics by the Density-Gradient Technique, American Society for Testing and Materials, West Conshohocken, Pa.

ASTM D3776. Standard Test Method for Mass Per Unit Area (Weight) of Fabric, American Society for Testing and Materials, West Conshohocken, Pa.

ASTM D4833. Standard Test Method for Index Puncture Resistance of Geomembranes and Related Products, American Society for Testing and Materials, West Conshohocken, Pa.

ASTM D5147. Standard Test Method for Sampling and Testing Modified Bituminous Sheet Material, American Society for Testing and Materials, West Conshohocken, Pa.

ASTM D5321. Standard Test Method for Determining the Shear Strength of Soil-Geosynthetic and Geosynthetic-Geosynthetic Interfaces by Direct Shear, American Society for Testing and Materials, West Conshohocken, Pa.

ASTM D792. Method A. Standard Test Method for Density and Specific Gravity (Relative Density) of Plastics by Displacement, American Society for Testing and Materials, West Conshohocken, Pa.

ASTM E96. Standard Test Method for Water Vapor Transmission of Materials. American Society for Testing and Materials, West Conshohocken, Pa.

Eldridge, T., and Harman, A. (2006). “Installing a bituminous geomembrane in extremely cold conditions.” Proc., IGS World Congress, Yokohama, Japan. 

Elliott, C. (2007). “Reducing the cost, increasing the quality and productivity in –30˚C with bituminous geomembrane for protecting the environment in a very rocky and cold region.” Proc., OttawaGéo 2007, Ottawa, Ont., Canada.

Huru, M., Palolahti, A., and Breul, B. (2008). “Use of bituminous geomembrane (BGM) liner for Agnico-Eagle Mine in Kittilä (Finland).” Proc., EuroGeo 4, Edinburgh, UK. 

NF P 84510. Détermination de la résistance au percement par granulats sur support rigide, Association Française des Applicateurs de Géomembranes, France.

XP P 84523. Détermination de la résistance au poinçonnement sous charge hydrostatique, Association Française des Applicateurs de Géomembranes, France. 

Natalie Daly, P.Eng, PMP, is managing director–Eastern North America for Axter-Coletanche in Montreal, QC, Canada.

Bernard Breul, Eng., is a civil engineer with Ecole Polytechnique Fédérale de Lausanne (Switzerland) and is based in Riom-ès-Montagnes, France.

All figures courtesy of the authors.