جستجوی مقالات مرتبط با کلیدواژه « روش های تجربی » در نشریات گروه « مهندسی معدن »

In this paper, the effect of the intermediate principal stress on the failure of different rocks and the accuracy of several 3D criteria in estimating failure of the true tri-axial tests results was investigated. Then, applying linear and nonlinear regression, a new 3D criterion was proposed that the criterion can successfully predict failure behavior of deep rocks with accuracy higher than other existing criteria.Failure criteria are relations between the strength properties of rock and applied stresses and used to describe the behavior and failure of rocks. This function is determined based on analytical and empirical methods. Some researchers neglect the effect of intermediate principal stress σ2 in the failure mechanism of rocks (2D failure criteria). However, there are experimental documents showing that the intermediate principal stress affects the failure behavior for at least some of the rocks (3D failure criteria. The intermediate principal stress has considerable effect on failure mechanism of very deep underground rock masses (such as hydraulic fracturing, wellbore and reservoir stability, underground storage in petroleum engineering). In this paper, the effect of the intermediate principal stress on the failure of five different rock types in 175 true tri-axial tests was studied. Also, the accuracy of several 3D criteria (such as Von Mises, Drucker-Prager and Pan & Hudson) in estimating failure of the tests results was investigated. Applying nonlinear regression, a new 3D criterion was proposed based on the true tri-axial tests results. Maximum, minimum, and intermediate principal stresses, along with uniaxial compressive strength and internal friction angle are used in the new criterion. In order to validation of the proposed criteria for other rocks, results of the true tri-axial tests for 190 specimens of seven different rock types were studied.The results of studies showed that the effect of intermediate principal stress is more significant in competent rocks than weak rocks and Pan & Hudson criterion gives the most accuracy with an MRAE equal to 0.24. Von Mises and Drucker-Prager criteria gave the next best results by MRAE respectively equal to 0.28 and 0.44. Also, RSQ and MRAE of the proposed criterion for all type of rocks are equal to 0.94 and 0.06 respectively that the criterion can successfully predict failure behavior of deep rocks with accuracy higher than other existing criteria.

The investigation and estimation of surface subsidence and ground settlement is an important aspect in the design of shallow tunnels in urban areas. Proper exploration could lead to correct measures and avoiding any damage to structures over and underground.
In this study, four sections of the east-western part of Tehran’s Metro Line 7 with the most potential for surface subsidence were chosen and studied. This part of the metro project is positioned in the young alluvial deposits of Tehran and consists mainly of fine grained soil. Ground settlement requires three dimensional design. Hence, FLAC 3D was used to investigate the surface subsidence of the ground along the tunnel route in sections mentioned above. One of the most important advantages of three dimensional design is the possibility of stepwise excavation, and to explore the effect of each excavation step on the surrounding ground. Hence, the stepwise excavation was carried out and continued in 1.5 m advancing stages, until the advancement stopped affecting the ground settlement at the point over the tunnel portal considered in the model.
Even though, analytical and empirical methods are unable to evaluate the effect of ground water and the effect of overburden due to the presence of structures and traffic at the surface, because of not installing the monitoring system, analytical methods suggested by Sagaseta, Loganathan and Poulos, Verruijt and Booker, and Bobbet, and also Peck’s empirical method were used to investigate the ground settlement in this project.
After using the various methods to study the four chosen sections of the metro line, and analyzing the settlement curves in these sections, it was concluded that the ground settlements is permissible (except the second section).