Determination of changes in fracture index of rocks by effects of environmental factors

In this study, it was aimed to determine the effects of different environmental conditions (dry, saturated, frozen, thermal shock and thermal aging) on some physico-mechanical properties and fracture toughness values of rocks from three different origins (i.e, magmatic, metamorphic and sedimentary). In the first stage, the physical, chemical, mechanical, mineralogical and petrographic properties of rocks were determined. In the second stage, the rocks are aged by exposing them to pre-determined environmental conditions for a certain period of time and then, some physico-mechanical tests (uniaxial compressive strength, point load strength, Brazilian tensile strength, Schmidt hardness, ultrasonic wave velocity) and semi-circular bending strength were applied on the aged rocks. In the third stage, models were developed to predict fracture toughness values from physico-mechanical properties using simple, multiple regression analysis and artificial neural network modeling. It was determined that the thermal shocking was the most weakening application among environmental conditions for physico-mechanical properties of rocks. In frozen condition it was observed that physico-mechanical properties and fracture toughness values of rocks increased. In the improved simple regression models, point load strength and Brazilian tensile strength were the best estimated mechanical properties of the fracture toughness as the R2 values greater than 0.97 were obtained. The performance of the models was considered successful because of below 10 when it is controlled with RMSE, MAE, MAPE values. Keywords: Rock mechanic, fracture toughness, fracture energy, environmental condition, semi-circular bending test, uniaxial compressive strength