Because chemical solutions can cause large changes in the microscopic surface such as increased porosity, weakening of the microscopic structures, creating intergranular cracks, etc. in the rock, and these changes lead to macroscopic scale fractures such as geological disasters like landslide and earthquakes, the investigation of the acid rain effect on the physical and mechanical properties of rock is of special importance. Due to their particular chemical composition, carbonate rocks can have high corrosion and solubility potential in the face of climatic or environmental conditions. Realizing the effects of the rock chemical solution of (alkaline and acidic) on the physical and mechanical properties of the rock, can provide basic and practical information about it’s mechanical behavior. In this study, after preparing the samples according to ISRM standard, physical and mechanical parameters including density, porosity, compressive wave velocity, shear wave velocity, permeability, rock durability index, indirect tensile strength were determined for the samples. Fracture parameters including, fracture toughness of first mode, second mode, combined mode, starting angle and the path of crack expansion were investigated as well. The processing of the samples under the environmental conditions loading was happened during 2, 4, 6, 8, 10, 12, 24 hours in 7 cycles. To eva‎luate the effect of the chemical solution, two cases of 24-hour and 48-hour have also been added. Altogether, 3 main cases are considered. This means that in the first case, all samples were processed at set time cycles and for the second case, in addition to the time cycles, the samples were initially immersed in the chemical solution for 24 hours. Finally, for the third case, the samples were first immersed in the chemical solution for 48 hours and then processed under the set time cycles after the specified time. Altogether, 63 density measurement tests, 36 permeability tests, 432 compression wave velocity tests, 56 shear wave velocity tests, 210 relaxation durability index test cycles, 50 indirect tensile tests and 72 fracture toughness tests were performed. Also, in order to study the crystalline limestone samples in more details, microscopic studies including thin section preparation and scanning electron microscopy (SEM) test were performed before and after processing the samples. The results obtained in this study demonstrated that the most important factor in changing the geomechanical properties of the crystalline limestone samples, is the presence of intergranular and to some extent intragranular microcracks due to intergranular cement dissolution and the change in the texture of the crystals due to the loading of environmental conditions. In general, the longer the immersion time of the samples for a high concentration chemical solution, the greater the damage to the sample. Finally, some physical properties such as porosity, permeability, water absorption percentage increase. Also, according to the mineralogy and strength of the sample, the maximum amount of changes for the relaxation durability index of the rock was equal to 9%. In investigating the tensile behavior of the rock, the softening state created on the samples, causes the samples to produce more secondary cracks when subjected to compressive load. In the study of the fracture toughness, the results showed that the fracture theory criteria based on the non-singular parameter T, such as the maximum modified tangential stress (MMTS) criterion, were well able to predict the fracture toughness curve for SCB samples under the loading environmental conditions. The reason for this is the dependence of these samples on the T parameter. The results also showed that the starting angle of crack of the samples is relatively consistent with the starting angle of crack after loading the environmental conditions predicted by the theory of failure criteria.

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مسعود چراغي، محمود بهنيا