It is estimated that more aggregate will be produced during the next 25 years than has been mined during the previous 100 years – Underground aggregate mines are an important strategic component to accomplish this demand while eliminating most of the obvious physical and visual impacts of a surface aggregate mining within urban communities. Furthermore, this alternative can be integrated into an efficient lands use planning system in order to capture the social-economic benefits of the underground space after depletion of the aggregate resource.
Aggregate derives much of its value from being located near the market. Transporting aggregate long distances increases its price significantly and may render distant deposits uneconomical. Therefore, aggregate operations commonly are located near population centers where conflicting land uses, zoning, regulations, and citizen opposition may preclude its development and production (Adapted from Langer et al., 2004).
In underground mines, surface developments, zoning laws, and environmental concerns are often less of an issue. Stripping requirements are eliminated and after use of the underground space can be developed (Adapted from Parker, 1996). Other added benefits such as working in a constant underground climate rather than variable surface climate and minimizing community concerns over dust, noise and air blast and vibration from blasting.
Drawbacks of underground mining relate primarily to the added health and safety hazards for the stone miners (Adapted From Iannacchione, 1999). Also, since underground aggregate mines are typically developed close to areas with relatively dense population, any possibility for subsidence must be eliminated. This requirement restricts the choice of mining method to basically Room-and-pillar and Long hole open stoping (adapted from Brown et al, 2010). The Room and Pillar method of mining is typically used for limestone deposits in the Eastern and Midwestern United States. Room excavations are 12 to 18 m wide to allow efficient operation of the large underground production equipment (Adapted from Esterhuizen et al., 2007).
Use of the underground space has contributed to sustainable development and to improvements to the environment and quality of life (Adapted from Brown et al., 2010). According to Sterling and Godard (2001), some of the key beneficial characteristics of underground space are:
- Simultaneous use of the superficial area;
- Setting for activities or infrastructures that are difficult, impossible, environmentally undesirable or less profitable to install above ground;
- Natural mechanical, thermal, and acoustic protection;
- Containment, protecting the surface environment from the risks and/or disturbances inherent in certain types of activities;
- Only visible at the point(s) where it connects to the surface;
In addition to these characteristics, underground aggregates mining spaces can be very attractive to the prospect of after use development, because its specific characteristics which include locations near or under heavily populated areas, good stoping geometry, typically accessible entrance by adit or gentle declines, relatively good ventilation, lack of flammable gases (e.g. methane) and in some cases logistics and infra-structure well developed (Adapted from Shinobe, 1997).
According to Brown et al. (2010), potential after uses for underground mining space can be grouped by the following categories:
- Energy: Compressed air storage, gaseous fuel storage, geothermal energy, hydroelectric pump storage, hydropower, liquid fuel storage energy from waste / bioreactor;
- Entertainment & Leisure: Dining room (restaurants), theme park, wedding venue, art gallery, museum, health & fitness center;
- Sport: Climbing wall, diving center, hypoxic running track, ice rink, motocross track, swimming pool, UG cycling track, indoor ski slope;
- Food & Drink: Cheese storage, fish farm, poultry farm, mushroom farm, wine cellar;
- Civil/Civic/Infrastructure: Below ground car parking, car battery recycling plant, salt barns, data store (both paper copy and electronic/magnetic media), desalination plant, electronic data center, sewage plant, shopping center, underground water reservoir;
- Medicine & Therapy: Medicinal plant cultivation, radon therapy (which would need careful handling from public perception and public health standpoints), salt therapy, sauna;
- Other/industry/storage: Cemetery, explosives factory, factory, munitions depot, protection bunker, waste disposal, tree nursery;
- Science & Technology: Dark matter research, elevator laboratory, science & engineering laboratory;
Warehousing bulky and/or low-cost material is the typical immediate after use for underground mining spaces in US. Usually, easily access from the surface, proximity to urban centers and major transportation systems, low construction cost, controlled climate and security are the key factors contributing for successful cases such as SubTropolis and Springfield developments in Kansas City, USA. Besides, warehousing, some promising uses includes agricultural activities such as mushroom cultivation, sericulture and floriculture.
As urban populations grow and spread, city planners and lands developers must consider strategies to accommodate multiple pressing demands such as land, energy, raw materials, quality of life and environment protection. In this context, underground spaces provide required flexibility in regards future sustainable alternatives.
Feasibility evaluation for underground aggregate operations needs to incorporate different scenarios and elements besides the typical elements of mining project. This may require direct involvement of experienced developers in early stages of the project, assessing subsequent after uses strategies as well as progressive rehabilitation and conversion phasing.
Are there any underground aggregate operations in your area? Would you suggest an after use aligned with the needs of your local community?
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Langer, W. H., Drew, L. J. and Sachs, J. S, “Aggregate and the Environment” Environmental Issues and Aggregate Mining in the 21st Century, Mineral Resources Team/SME, USGS and American Geological Institute Alexandria, VA, USA. (2004).
Parker, J.,“Everybody Goes Underground Eventually”, Aggregate manager, June 1996, pp. 30-35. (1996).
Iannacchione, A.T.,“Analysis of pillar design practices and techniques for U.S. limestone mines,” Trans. Inst. Min. Metall., Sect. A: Min. Industry, Vol. 108, September-December, pp. A152-A160. (1999)
Esterhuizen, G.S., Dolinar, D.R., and Ellenberger, J.L.,“Pillar Strength and Design Methodology for Stone Mines” Proceedings of the 27th International Conference on Ground Control in Mining, July 29 – July 31, 2008, Morgantown, WV, USA. (2007).
Shinobe, A.,“Economics of Underground Conversion in an Operating Limestone Mine”, M.Sc. Thesis, McGill University, Montreal, Canada. (1997).
Brown, T. J., Coggan, J. S., Evans, D. J., Foster, P. J., Hewitt, J., Kruyswijk, J. B., Millar, D. L., Smith, N. and Steadman, E. J., , “Assess the feasibility of the underground mining of aggregates” Aggregates Strategic Research Programme, Department for Environment Food and Rural Affairs, Nottingham, UK. (2010).
Feature Image: Sub-terranean SubTropolis industrial complex in Kansas City, MO. Author: ErgoSum88
Figure 1: Marble quarry at Carrara, Province Massa-Carrara, Italy. Author: Lucarelli
Figure 2: MINOS detector in the Soudan Underground Mine State Park . Author: Jon ‘ShakataGaNai’ Davis
Figure 3: Saint Kinga Chamber in Wieliczka Salt Mine, Poland. Author: Rodw
Figure 4: Cheeses stored at Wookey Hole Caves. Author: Rodw