Quarrying in Karst: Geotechnical Estimation of Environmental Risk

Quarrying in karst poses potential environmental risk. Historically, well-documented, large-scale negative impacts related to extensive and deep quarries, include dewatering of aquifers, changes in groundwater flow, and induction of land subsidence and sinkholes. Estimating and mitigating risk prior to quarrying are difficult. Some geotechnical techniques in karst may be unreliable or imprecise owing to a high degree of anisotropy and heterogeneity transmitting groundwater exclusively through fractures (secondary porosity) and dissolutionally enlarged openings (tertiary porosity). Surficial geophysical investigations, (e.g. electrical resistivity, ground-penetrating radar, seismic exloration, lineament analysis) are useful but rarely definitive in characterizing a quarry site. Borehole geophysics, although very precise within each well, may not reflect the true configuration of conduit flow within the footprint of the quarry. Statistically, wells drilled in dense bedrock with wide fracture spacing may intersect few, if any, significant openings. Geophysical parameters and pump tests from such wells may lead to erroneous hydrogeologic conclusions about the site, including the areal extent of influence of a quarry. Dye-trace studies typically provide a better indication of potential risk. Quarries close to zones of recharge may introduce steep hydraulic gradients near the excavation, augmenting discharge into the opening. Conversely, quarries distant from such zones may produce much gentler gradients and have a reduced environmental impact.