In this study, we investigate the effect of wet an‎d dry periods on the strength an‎d permeability of the underlying Red Formation (silty san‎dstone). Given the importance of these two types of rocks in construction an‎d geotechnical engineering applications, studying their behavior under variable moisture conditions is of particular importance. Samples with a diameter of 62 mm an‎d a height of 120 mm were taken from the study area an‎d tested in control conditions (period zero) an‎d after two an‎d four wet-dry periods. The tests performed included uniaxial compressive strength (UCS), Youngʹs modulus, indirect tensile strength (Brazilian), triaxial compressive strength, durability, an‎d permeability tests. Laboratory results showed that the uniaxial compressive strength decreased from about 43 MPa in the control sample to 15.24 MPa in the second period an‎d 7.47 MPa in the fourth period. Youngʹs modulus also decreased from about 4500 MPa to 1393.5 an‎d 825 MPa in the second an‎d fourth periods. Brazilian tensile strength decreased from 0.99 MPa in the control sample to 0.42 an‎d 0.24 MPa. In the triaxial compressive strength test, it also decreased from 61.95, 70.53, 77.70 in the control sample to 39.76, 45.73, 48.71 in the second period to 34.32, 40.43, 48.38 MPa in the fourth period. Also, the permeability coefficient increased from 7.82×10-5 m/s in the control sample to 1.30×10-4 m/s in the fourth period. These trends indicate a continuous weakening of mechanical properties an‎d a significant increase in rock permeability due to repeated wet-dry periods. In addition, the durability test also showed a decrease in the mass of the samples from 476.2 g in the first period to 449.6 g in the second period (equivalent to a decrease of about 6.5%), which confirms the weakness of the grain cohesion under the effect of wet-dry cycles. In addition to mechanical an‎d hydraulic tests, numerical modeling was performed using Phase2 software to investigate the changes in the strength reduction factor (SRF) in different zones of the sample. The results indicate that in the control sample (period zero), the strength reduction factor was obtained as 2.55, 1.35, an‎d 2.16, respectively, which indicates the high stability of the sample in the initial conditions. By applying wet-dry cycles, a decreasing trend in stability was observed; In the second period, the SRF values reached 1.89, 1.11, an‎d 1.82, an‎d in the fourth period, they reached 1.14, 1.06, an‎d 1.72. These changes indicate that although some zones recorded local increases in values, the overall trend indicates gradual weakening an‎d stress concentration in specific parts of the sample.

امين ازهري

هاجر شرع اصفهاني

عليرضا باغبانان , ابراهيم قاسمي