Inżyniersko-geologiczne badania masywów krasowych i generacji ich spękań

Witold Cezariusz Kowalski



Results of engineering-geological studies, carried on karst massives, point out, that the main factors for the karst development are: not only the karst corrosion, which intensity depends - among other factors also – on the state of stress, 'the specific surface and shape of corroded rocks but also on the self-acting strain cracking. The last one was developed in the defined conditions, when the values of the horizontal tensile stresses in roofs and floors of voids in the rock massif exceed the values of the tensile strength of rock (Fig. 1a). The strain cracking in roofs of voids causes a self-acting forming of the new elliptic roofs of the transforming voids and a covering the old floors of voids with sharp-edged debris (Fig. 2 and 1). Two generations of cracks in karst massives were distinguished: the older one - the pre-karst cracking, that makes easier to develop the karst process from their beginning, and the younger one - of the self-acting strain cracking in roofs and floors of the voids, that are broadening by corrosion on their walls. The vertically situated above each other voids may join and form vertical karst holes as results of self-acting strain cracking in roofs and floors of the voids (Fig. 3). The vertical extent of cracks over and above the voids diminish with depth of their occurrence (Fig. 4), when values of the horizontal compressive stresses increase in the rock massif. To describe properly the state of a karst massif and to forecast a karst development in it is necessary to take into consideration positions of underground water levels in the past, nowadays and for the future – especially positions of the highest levels, above which the vertical karst holes develop, and the lowest ones, below which as a rule the karst corrosion is practically stopped and does not change shapes of voids (Fig. 2). The self-acting strain cracking in roofs and floors of karst voids is the very essential factor for the development of karst caves particularly in the zone of the ground water table fluctuation.