جستجوی مقالات مرتبط با کلیدواژه "همگرایی" در نشریات گروه "مهندسی معدن"

Convergence-confinement is one of the most popular methods which is used for analysis of stress and strain fields around a circular opening excavated in rock masses. It is assumed that the circular tunnel is excavated in a continuous، homogeneous، isotropic، initially elastic rock masses under hydrostatic loading. Selection of a suitable failure criterion is extremely important in the analysis since it affects the plastic zone and obtained displacement and stress field around the opening. Brown et al (1983) proposed a stepwise procedure based on Hoek-Brown criterion to obtain stress and displacement around a circular opening. A similar stepwise procedure is implemented in this study for Mohr-Coulomb criterion. Then the effect of Mohr-Coulomb and Hoek-Brown criteria on ground response curve is investigated for various models of rock mass behaviors. Finally a sensitive analysis is implemented for Mohr-Coulomb and Hoek-Brown criteria. By a comparison of Hoek-Brown and Mohr-Coulomb criteria، it can be concluded that the relative displacement in Mohr-Coulomb criterion is at least 5 times more sensitive than that in Hoek-Brown criterion to variation of strength parameters. It is obtained that varying rock mass strength parameters develops more relative deformation for medium-quality rock masses. Therefore، it should be carried out to preserve the inherent strength of rock masses by controlled blasting or mechanical excavation، especially for medium quality of rock masses (often with elastic-strain softening behavior).

Convergence in the galleries of underground tunnels, caused by the displacement of the ceiling, floor and walls, strongly affects the time-dependent stability of the gallery. By estimating the displacement value, the load that will be induced to the support system can be determined. By calculation of the gallery convergence caused by displacement of floor, ceiling and walls, the pressure applied on the support system can be predicted and by thus appropriate design of support system can be done. Yet, analytical and numerical models to determine the convergence of mine galleries have been presented. Nonetheless, presentation of a simple and empirical model able to predict the convergence of galleries of coal mines, far from complexities of numerical equations, can be focused by miners. In rock galleries, two kinds of instabilities often occur. In the first case, gallery instability occurs with a sudden destruction. In this case, discontinuities divide the rocks surrounding the gallery into particles and these particles can move or rotate. In the second case, instabilities often occur in very deep layers and with high initial stresses and with progressive convergence. In this paper, field studies and measurements showed that present numerical relations for prediction of final convergence, ceiling heave and wall convergence of galleries of coal mines are not applicable for convergence determination of the galleries of Tazareh Mine. Thus, a relation for more accurate estimation of galleries of Tazareh Mine, specially the gallery K21 (because of data accessibility of this gallery and similarity of geometrical-mechanical properties of this gallery to other galleries) has been presented. For this purpose, at first, effective parameters in such convergences as depth, coal layer thickness and slope, conditions of gallery floor rocks, mining time and destruction conditions were determined. In addition to parameters effective in convergence, a criterion for the estimation of the convergence value in underground coal mines galleries is presented by means of simulation of the K21 gallery of Tazareh Mine parameters. The multiple linear regression analysis was used to find the coefficients of the independent parameters by considering all effective parameters in convergence in a way that a linear relation existed between the independent and the relative parameters. The presented equation was validated by investigating the data being normal, constancy, variance and linearity of the relation between the independent and the relative parameters. A comparison between the values calculated by using the presented criteria and the real measured values in the monitoring stations showed that the presented model is highly capable of assessing of the mentioned gallery. By this empirical relation, estimation of convergence of coal galleries, in which the coal layer has different slopes, can be done.

Nowadays, convergence-confinement method is one of the most important methods in determining support systems for both underground circular and non-circular spaces. Selecting an appropriate constitutive model including elastic-perfectly plastic, elastic-brittle-plastic and elastic-strain softening models has a significant role in the application of this method. In some cases, the difference of displacements resulting from choosing different constitutive models is more than 100%. In this research, we attempted to investigate the effect of different constitutive models on the ground reaction curve and plastic zone made around a circular opening. It has been supposed that a rock mass is initially carries an elastic behavior and undergoes an isotropic pressure,. The failure criterion used here is non-linear Hoek-Brown yield criterion. The problem is solved in a stepwise procedure proposed by Brown et al (1983), in which rock mass strength parameters change in a stepwise method from the peak to the residual values. Finally, a sensitive analysis is performed on the Hoek-Brown strength parameters.