Wyniki badań nad sprężeniem i odprężaniem się marmuru z kamieniołomu Dębnik

Abstract

RESULTS OF RESEARCH ON STRAINING AND UNSTRAINING OF MARBLE FROM DĘBNIK QUARRY

Within a rock complex, each type of rock is under strain and in a corresponding state of deformation. From the moment of removal of a rock from its stratum, unstraining sets in and its elastic deformation disappears.

In order to determine the intensity of this straining, the course of unstraining and the changes in momentary resistance to pressure of the rock during this process of unstraining, the author carried out tests using samples of marble taken from the Dębnik quarry. This Dębnik marble is a finegrained limestone of dark-grey colour calmed by bituminous admixtures, with veinlets and concentrations of calcite. In several instances, the diversely directed calcite veinlets (Plate I) (caused considerable divergences in the results of tests.

The samples tested were cut from three marble blocks, each derived from a different part of the quarry. Part of these samples were coated with paraffine in order to determine the eiffect of air upon the resistance of the rock during the period of its unstraining. The author presented the resuits of these tests in Tables 2, 3 and 4. The changes in rock resistance during unstraining are shown in Figs. 8, 4 and 5.

The tests indicate that rock freshly mined from its bed may undergo, simultaneously with its unstraining, physico-chemical reactions caused by the action of air as well as by structural processes brought about by inner stresses developing at the moment when unstraining reaches some determined magnitude. Each of these processes bears on the resistance of the rock sample. During the period that these processes take place, the rock resistance is a variable; it becomes a constant after these processes are terminated.

Using identical rock samples and carrying out the resistance tests at different periods before the processes mentioned above are terminated, different results are obtained; these differences may exceed 50%. Simultaneously with the course of the processes discussed, other properties·of the rock are also subject to changes, such as: hardness, abrasiveness, porosity, volumetric weight, permeabIlity, etc.

For improving quarry activties and sculptural work, the appreciation of the necessity of unstraining the rock is an essential matter.

In order to determine the real constant properties of rocks, toots should be undertaken using fully unstrained samples. Hitherto, this. fundamental condition is nor taken into consideration in rock tests.