Assessment of hydraulic conductivity of disturbed and undisturbed rock masses in Tunçbilek lignite basin, Turkey
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Hydraulic conductivities of rock masses in Tunçbilek lignite basin, western Turkey, were determined by analytical methods and seepage analyses. In situ hydraulic conductivity of lignite, clay-bearing rocks and disturbed rock masses in the basin was determined by utilizing the inversed auger hole method. The hydraulic conductivity values of the lignite and clay-bearing rocks were determined by the field testing to be ranged from 7.88×10−7 to 2.24×10−6 m/s and from 2.49×10−7 to 1.11×10−5 m/s, respectively. Excavation and blasting processes for mining activity eventually caused a significant increase in the fracture frequency. Therefore, hydraulic conductivity values of disturbed/blasted rock masses were measured as two or three order magnitudes higher than those measured on the undisturbed clay-bearing rock masses. To get a further understanding of the hydraulic properties of studied rock masses, seepage analyses were also performed on rock masses left as a pillar between an underground mining gallery and an adjacent abandoned open-pit mining lake. According to the analytical solution based on the Dupuit-Forchheimer approximations, the average hydraulic conductivity value of the pillar consisting mainly of marls, claystone and lignite layer with a variable thickness was calculated as 1.2×10−6 m/s. Seepage analyses were also performed to predict water inflow to the gallery in the case of possible blasting and subsidence-related disturbance problems as well as a rise in the level of the open-pit lake. Based on the results obtained, it can be concluded that subsidence or blasting-induced disturbance of rock masses can cause excessive water inflow into the underground galleries to jeopardize the safety of mining activities. © 2021, Saudi Society for Geosciences.