Odkształcalność piaskowców w świetle zmian wilgotności i smukłości próbek

Abstract

Deformability of sandstones in view of changes in humidity and slenderness ratio of samples.A b s t r a c t. Natural humidity of rocks in the Upper Silesian Coal Basin results from the influence of mining activities and dewatering the rock mass. The state of humidity which best approximates laboratory rock tests to the conditions in the exploited rock mass is the capillary saturation state. Deformation properties of sandstones (Young’s modulus, post-peak failure modulus, critical strain, residual strain) were determined for samples of slenderness ratio of 1 and 2, which were loaded in a servo-controlled testing machine. In the samples of sandstones of different slenderness ratio, values of Young’s modulus decreased for the samples in dry-air condition and capillary saturation state. In the samples of rocks of different slenderness ratio, tested in the same state of humidity, an increase in the value of Young’s modulus was observed. The increase depends on grain size. Post-peak failure modulus of sandstones shows similar trends of changes depending on slenderness ratio, state of humidity of the samples and their grain size. In the conditions when the samples of sandstones of slenderness ratio of 1, were tested in two states of humidity, values of critical strain decreased by a few per cent. For the samples of greater slenderness ratio, which also were tested in two states of humidity there was an increase in the value of critical strain and in humidity. For the samples of slenderness ratio of 1 and 2 tested in dry-air condition and in capillary saturation state there was a decrease in the value of critical strain by a few tens percent. The trends of changes in values of residual strain are the same as of critical strain. Based on the conducted tests it was shown that humidity and slenderness ratio of the sandstone samples influence differently their deformability. Humidity has a greater influence on the value of Young’s modulus than slenderness ratio of the tested samples. For critical strain and residual strain it was demonstrated that slenderness ratio of the samples has a greater influence thanhumidity. Moreover, a greater influence of the value of residual strain, in comparison with the values of critical strain, was observed for sandstone samples of lower slenderness ratio.