WŁAŚCIWOŚCI GEOMECHANICZNE MIOCEŃSKICH SOLI KAMIENNYCH

Abstract

GEOMECHANICAL PARAMETERS OF MIOCENE ROCK SALTAbstract. Core samples from the Miocene salt deposits of Lezkowice and Siedlec-Moszczenica were tested for uniaxial compression and uniaxial tension strength and for creep properties. As a result of these tests the following parameters were calculated: bulk density, compressive strength, tensile strength, Young's modulus and Poisson's ratio. Axial, transverse and volume strain characteristics of rock salt samples are described by unlinear course in the whole range of stress. Dilatancy boundary appears at axial stress from 8.4 to 14.4 MPa (about 35% Re). All the obtained parameters indicated that strength of rock salt is influenced primarily by a terrigenous material content. In most cases, its high content increases both compressive and tensile strength. However, not only the content of terigenous material is important, but also its concentration form such as laminas and intergranular space infill. Graining is less important but generally the strength value decreases with a grain size increase. In spite of this fact, the lowest strength is typical for vari- grained salt samples. Moreover, interesting is a high strength of salt sample characterized with directionally elongated grains. Tectonic processes which produced such salt texture caused its strengthening. It is probably connected with better grain to grain fitting or partial recrystallization. Sandstone samples with anhydrite exhibit with the highest compressive strength value among the tested barren rocks. This value can be reduced by the occurrence of laminas and flames of entherolithic anhydrite whose boundaries are the natural weakening surfaces. Creep dependence on loaded stress was noticeable in the tests. Furthermore, the higher stress values correspond with the greater creep intensity. Creep curves are characterized by variable values both for each rock salt type and within the same type. The values resulted from changeability in compressive strength values of all the samples analyzed.