V. Sarfarazi; K. Asgari; Sh. Mohamadi Bolban Abad
Abstract
The interaction between an internal hole and two surrounded joints under a uniaxial compression are examined using the experimental and discrete element procedures. Inside the concrete sample, two notches and an internal hole are created. The joint angle change from 0° to 90° with an increment ...
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The interaction between an internal hole and two surrounded joints under a uniaxial compression are examined using the experimental and discrete element procedures. Inside the concrete sample, two notches and an internal hole are created. The joint angle change from 0° to 90° with an increment of 30°. The distances between the joint and the internal hole are 2 cm and 3 cm. Also the numerical models are provided. The joint angle change from 0° to 90° with an increment of 15°. The distances between the joint and the internal hole are 2 cm, 3 cm, and 4 cm. The compressive strength is 7.2 MPa. The rate of loading is 0.005 mm/s. The experiment indicates that the failure process is significantly dependent on the notch angle and the joint distance from the hole. The pattern of fracture and mechanism of failure of joints affect the shear strengths of the samples. The models with joint angles of 30° and 60° have a less compressive strength since the pure tensile failure occurs in these configurations. The model strength decreases with decrease in the join spacing. In fact, in the case that the joint spacing is 2 cm, the interaction between the hole and the neighboring joint is so strong. Consequently, the compressive strength is declined. In both approaches of the numerical simulation and experimental methods, the pattern and strength of failure are identical.
V. Sarfarazi; K. Asgari
Abstract
Particle Flow Code in Two Dimensions (PFC2D) was used in order to examine the influence of single tunnel and twin tunnel on the collapse pattern and maximum ground movement. Since first PFC was calibrated by the experiments, the results obtained were rendered by a uniaxial test. Further, a rectangular ...
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Particle Flow Code in Two Dimensions (PFC2D) was used in order to examine the influence of single tunnel and twin tunnel on the collapse pattern and maximum ground movement. Since first PFC was calibrated by the experiments, the results obtained were rendered by a uniaxial test. Further, a rectangular model with dimensions of 100 m ˟ 100 m containing both the central tunnel and twin tunnel was built. The center of the single tunnel was placed 25 m under the ground surface, and its diameter changed from 10 m to 35 m with an increment of 5 m. The center of the twin tunnel was situated 25 m under the ground surface, and its diameter was changed from 10 m to 30 m with an increment of 5 m. For measurement of the vertical displacement, one measuring circle with a 2 m diameter was opted on the ground surface above the tunnel roof. The average of the vertical movement of discs covered in these circles was determined as a ground settlement. A confining pressure of 0.01 MPa was applied on the model. The uniaxial compression strength was 0/09 MPa; the results obtained depicted that the tunnel diameter controlled the extension of the collapse zone. Also the vertical displacement at the roof of the tunnel declined by decreasing the tunnel diameter. The ground settlement increased by increasing the tunnel diameter.
V. Sarfarazi; K. Asgari
Abstract
In this investigation, the impact of confining pressure on the tensile strength obtained by point load test (PLT) is examined by particle flow code in two dimensions. In this regard, at first, a numerical model is calibrated using the Brazilian experimental test results. The tensile strength of the model ...
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In this investigation, the impact of confining pressure on the tensile strength obtained by point load test (PLT) is examined by particle flow code in two dimensions. In this regard, at first, a numerical model is calibrated using the Brazilian experimental test results. The tensile strength of the model material is equal to 2.5 MPa. Secondly, PLT is performed on the numerical models with dimension of 15 cm × 50 cm. The rectangular models are tested by PLT under the presence of the confining pressure. The loading rate is 0.001 mm/min, confining that the pressure is changed with the 13 different values of 0 MPa, 0.002 MPa, 1MPa, 1.5 MPa, 2 MPa, 2.5 MPa, 3MPa, 3.5 MPa, 4 MPa, 5MPa, 6 MPa, 9 MPa, and 11 MPa. The results obtained show that the vertical tensile crack develops through the model under a low confining pressure, while several shear bands are developed in the models under a high confining pressure. The number of shear cracks is augmented by augmenting the confining pressure. Is(50) is the augment by augmenting the confining pressure. Also a new criterion is rendered in order to determine Is(50) based on the confining pressure.
V. Sarfarazi; K. Asgari; Sh. Mohamadi Bolban Abad
Abstract
In this work, we investigate the interaction between tunnel and surface foundation in two dimensions by the particle flow code. At the first stage, the PFC calibration is conducted using the experimental test results rendered by a biaxial test. Then the simulation of a biaxial test is performed by confining ...
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In this work, we investigate the interaction between tunnel and surface foundation in two dimensions by the particle flow code. At the first stage, the PFC calibration is conducted using the experimental test results rendered by a biaxial test. Then the simulation of a biaxial test is performed by confining a rectangular sample inside four walls. The walls are located at the top and bottom simulated loading plates and the adjacent walls are located at the left and right simulated sample side confinement. The velocities of the top and bottom walls are determined, and they are used for loading the sample in a strain-controlled mode. The respond of the material is evaluated by following the diverse stress and strain quantities. The axial deviatoric stress versus the axial strain for biaxial test on the bonded granular material is drawn, and then the Mohr's circle is drawn in order to reach the failure envelope of laboratory. Secondly, a rectangular model with dimensions of 10 m 10 m containing a central tunnel and a surface foundation is built. The tunnel is situated in sixteen different positions below the foundation. The foundation moves downward with a velocity of 0.016 mm/s. The results obtained show the position of the tunnel controlling the failure volume. Also the vertical displacement at the roof of the tunnel decreases by increasing the vertical spacing between tunnel and foundation. The settlement beneath the foundation increases by reducing the vertical spacing between the tunnel and the foundation. The settlement beneath the foundation decreases by augmenting the horizontal spacing between the tunnel and the foundation.
V. Sarfarazi; H. Karimi Javid; K. Asgari
Abstract
The experimental and numerical methods were used to investigate the effects of joint number and joint angle on the failure behaviour of rock pillars under a uniaxial compressive test. The gypsum samples with dimensions of 200 mm × 200 mm × 50 mm were prepared. The compressive strength of ...
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The experimental and numerical methods were used to investigate the effects of joint number and joint angle on the failure behaviour of rock pillars under a uniaxial compressive test. The gypsum samples with dimensions of 200 mm × 200 mm × 50 mm were prepared. The compressive strength of the intact sample was 7.2 MPa. The imbeded joint was placed inside the specimen. The joint length was 6 cm in a constant joint length. There were several numbers of cracks including one, two, and three cracks. In the experimental tests, the angles of the diagonal plane with respect to the horizontal axis were 0, 30, 60, and 90 degrees. The axial load was applied to the model with a rate of 0.01 mm/s. In the fracture analysis code, the angles of the diagonal plane with respect to the horizontal axis were 0, 15, 30, 45, 60, 75, and 90 degrees. A constant axial load of 135 MPa was applied to the model. The results obtained showed that the failure process was mostly dependent on the angle and number of the non-persistent joint. The compressive strength of the samples was dependent on the fracture pattern and the failure mechanism of the discontinuities. It was shown that the tensile cracks were developed whithin the model. The strength of the specimens increased by increasing both the joint angle and joint number. The joint angle of 45° KI had the maximum quantity. The stress intensity factor was decreased by increasing the joint number. The failure pattern and failure strength were analogous in both methods, i.e. the experimental testing and the numerical simulation methods.
