COMPARATIVE ANALYSIS OF THE MOISTURE AND POROSITY INFLUENCE ON THE STATIC AND DYNAMIC ELASTICITY MODULUS

Elastic characteristics of rocks can be influenced by various factors of different nature, both external and internal. Among internal factors, moisture content and porosity significantly influences static and dynamic elasticity modulus. Humidity has a decisive influence on the elastic behavior of rocks, leading to an artificial increase of the elastic characteristics values dynamically determined and having an adverse effect on the elastic characteristics determined statically. An increase in porosity leads on the one hand, to a decrease in the values of elastic characteristics determined dynamically and statically, and on the other hand (with moisture intake) it can lead to an increase in elastic characteristics determined dynamically. This paper presents the results of tests performed on various types of igneous rocks, submitted to static and dynamic stresses. Tests were performed in Geo-Mechanics Laboratory within the University of Petrosani. The calculated values of static and dynamic elastic modules for different types of igneous rocks were analyzed and compared in the laboratory, both for dried samples with natural moisture and for saturated samples. Under the influence of moisture and porosity, modules showed significant variations even within the same type of rock. Moisture content has a large enough influence on the elastic characteristics determined dynamically, meaning that dynamic modulus value increases for intact rocks, proportionally with the water content increase. This behavior may be due to the fact that the elastic wave propagation speed is higher in water than in air, and as the water saturation of the sample the environment becomes more homogeneous. It was also found that through rock drying, the phenomenon can be reversed only if the components did not react with minerals in the water saturation process.