Prognozowanie metodą modelowania analogowego dopływów wody do kopalń pracują­cych w skałach szczelinowo-krasowych

Abstract

Forecasting of ground-water inflow into mines in fissure-karst horizons using the electric analogy simulation method The analog simulation method is applied in hydrogeology chiefly for ground-water flow investigation in porous rocks, rarely being applied for fissured and karst fissured rocks. This is caused by the fact that the principle of the simulation method is the validity of Darcy’s Law while real movement of ground-water in karst-fissured rocks is supposed to be turbulent in character. In this paper the authors present an example of water inflow prognosis to an ore mine operating in fissured and karst-fissured, dolomites and limestones. The authors’ investigations have proved that in some conditions the analog simulation method can be applied for these kinds of aquifers with accuracy sufficient for practical purposes. In the geological profiles of investigated area, four aquifers appear: Quaternary, Jurassic, Triassic and Paleozoic (Fig. 1). The Triassic water-bearing horizon, which was the object of simulation investigations is represented by limestones and dolomites of Muschelkalk and Roethian age. The ground-water circulation in the investigated filtration area is very complicated, influenced by the specific recharge and discharge conditions of water-bearing horizons as well as the geological structure. Moreover, these aquifers are interconnected by means of different types of hydraulic contacts (Wilk, Motyka, 1977). For several years, large quantities of ground- -water are being extracted from the Triassic water-bearing horizon by ore mines and by municipial as well as industrial water supplies. This caused the radical change of natural water conditions, manifested by the increase of hydraulic gradients, the change in direction of ground-water flow, decrease of river flow rate, extinction of springs etc. These changes are registered with the help of numerous observation wells. Observations indicate that at present there still occurs an unsteady flow, of ground- -water in the investigated area as result of man’s activity and particularly of mining operations. The modelled area covered ca 500 km2, and the considered ground-water filtration field was divided into square blocks x = [delta] y = 1250 m. The investigations were carried out by means of the electric RC-analog simulating computer AP-600. The initial conditions, i. e. the coefficient of transmissibility, the coefficient of storage and the distribution of hydraulic head in the investigated aquifer were admitted on the basis of numerous laboratory and field investigations. They contained among others, the pumping tests and investigations in piezometric wells. The boundary conditions, i. e. hydraulic head and flow change function on the limits of investigated filtration ground-water field and in the characteristic points of its interior were accepted on the ground of hydrogeological map analysis and of statistic data concerning the quantities of water pumped from mines and ground-water supplies. In order to make hydrological paramétrés more accurate and to verify the admitted initial and boundary conditions, the control simulation was carried out assuming the ground-water flow conditions disturbed by mine water pumping and municipial ground-water supply activities. The investigations were carried out for several time horizons. During these investigations the hydrogeological paramétrés accepted in the calculation scheme and external as well as internal boundary conditions were verified. As a result, the distribution of hydraulic head, very similar to the initial situation in natural conditions (Fig. 5) and the significant approximation to the situation observed in the period during the unsteady flow (Fig. 6) were acquired in the model. At the same time, the inflows to the mines and municipial water supplies acquired in the model for the investigated period were different than the measured from 3% to 7%. Basing on these results the inflow prognosis for every year till 1985 was elaborated. This prognosis was elaborated for two variants of mine surface expansion. The results presented in the Table 3 and in the Fig. 11 indicate that expansion direction and the size of the expansion of the mine exploited area should not considerably influence the water inflow. The piezometric surface formation for selected years and for two K 3 mine development variants are represented by Fig. 7—10. In conclusion, the authors discuss the entity of acquired simplified actual hydrogeological conditions and estimate their possible effects for accurate results.