While the term overburden may indicate a uniform composition and standard features, the actual material is anything but constant. Each mine produces a different type of overburden, and each new layer of material also changes in composition. This fact alone makes it a challenging material to contain since one day of work may produce a heavy clay while another extracts a loose sand. Yet, that’s far from the only issue making overburden a difficult material to contain. Make sure that leachate and erosion from the piles of excess material do not become an issue by understanding exactly what makes overburden a challenge to store.
Weight
The sheer size of most overburden piles makes them difficult to keep lined with any standard material. Each foot of material stacked on top can add thousands of pounds to the total weight of the pile. The heavier the pile, the more force there is pressing down on the liner below. This will eventually stretch and rip most materials, even those designed to withstand industrial and commercial uses. Reinforced polyethylene is an exception to that rule because it’s stronger and more durable than other impermeable geomembranes. In addition to using a stronger and more reinforced liner material, storing overburden in multiple smaller piles is recommended over trying to build just a few larger and taller ones. The risk of collapse and landslide is far lower when smaller and carefully shaped piles are used rather than the tall narrow ones that are standard for the industry.
Abrasiveness
Like most mining materials produced by excavation or blasting, overburden from surface mining is a highly abrasive material. Sand itself is naturally abrasive, but the addition of bits of rock and gravel makes the mixture even harder on liner materials used to contain it. Even the clay that is mixed into the overburden can put wear and tear on the liner if it has a high silica content, which is common with material that occurs over ore and coal seams. Reinforced liners, like RPE, are highly recommended whenever a project calls for storing or containing an abrasive material like overburden.
Mixed Materials
When piling the material all in one heap, incompatible layers can laminate and cause collapses and landslides later. Loose materials stacked between thicker layers collapse, leaving the entire pile unsteady. One option is sorting the materials based on their textures and other physical characteristics. If the overburden materials will be reused as building materials, or for other purposes besides filling in the mine, sorting and grading are likely worth the effort for that reason alone. Even for mixed materials that will be used without separation, it’s best to build the storage heaps with care so that lamination doesn’t become an issue.
Drying
Natural drying effects from wind and evaporation are often seen as a posited part of storing overburden in heaps since the lighter material is easy to move. However, the same drying effect also leads to dust production if the surface of the mound is unstable and exposed to the wind. In most cases, applying water to the stored overburden is preferred to keep drying from triggering dust problems and allowing the material to simply blow away. This requires the use of an impermeable barrier at the bottom, most likely a geomembrane liner, to keep leachate from seeping through the soil and into the surrounding environment.
Don’t let the challenges of overburden containment and storage stop you from succeeding. The industrial grade liners available from us here at BTL Liners are tough enough to handle all of these issues and more. The reinforced polyethylene material is the key to creating a liner that won’t collapse, tear, or rip over the years of use.
