Exploitation
Morteza Javadi; Ashkan Shahpasand; Shahrbanou Sayadi; Arash Shahpasand
Abstract
The stratified-sedimentary rock mass, as the typical host ground of coal mine tunnels, is characterized by highly non-isotropic deformation due to the very persistent discontinuity of bedding planes. This study evaluates the effect of tunnel location relative to the host ground strata on the excavation-induced ...
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The stratified-sedimentary rock mass, as the typical host ground of coal mine tunnels, is characterized by highly non-isotropic deformation due to the very persistent discontinuity of bedding planes. This study evaluates the effect of tunnel location relative to the host ground strata on the excavation-induced displacements around a coal mine tunnel driven along the inclined coal seam. To achieve this goal, a calibrated finite element method (FEM) numerical model based on field monitoring displacements was developed for the coal mine tunnel at a depth of 300 m. This calibrated numerical model was then utilized to investigate the effect of the horizontal location of the tunnel on the induced displacement field through sensitivity analysis. Finally, the sensitivity analysis results were compared in terms of displacement components around the tunnel. The results of this study demonstrate a reasonable level of accuracy (for practical demands) of the calibrated numerical model, with an average error of about 8% for maximum displacements at measured points. The numerical models show an asymmetric spatial distribution of displacements around the tunnel due to the anisotropy of the rock mass, especially in the case of inclined layers. The arrangement of weak-strength coal and intercalary stone layers relative to the excavation line of the tunnel plays a key role in this issue. The critical state of displacements (maximum displacement in sensitivity analysis) occurs where the intersection line of the coal-intercalary stone is tangent to the tunnel excavation line. Additionally, the excavation-induced displacement decreases as the distance between the coal-intercalary stone interface and the tunnel increases, with a distance of about 1.5 m suggested for practical applications.
Rahul Shakya; Manendra Singh
Abstract
Due to fast urbanization, there is a shortage of above-ground surfaces. Thus to reduce this shortage of above-ground surface, underground tunnels are constructed beneath the structure for transportation purposes. As a result, it is critical to understand how earthquakes affect underground tunnels, so ...
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Due to fast urbanization, there is a shortage of above-ground surfaces. Thus to reduce this shortage of above-ground surface, underground tunnels are constructed beneath the structure for transportation purposes. As a result, it is critical to understand how earthquakes affect underground tunnels, so that people's lives can be saved and service levels can be maintained. Underground constructions cannot be considered entirely immune to the impacts of ground shaking, as evidenced by the Kobe earthquake (1995), the Chi-Chi earthquake (1999), and the Niigata earthquake (2004), when some underground structures were severely damaged. A typical section at Chandani Chowk of DMRC (Delhi Metro Rail Corporation) tunnels, New Delhi, India, has been analyzed by using the finite element method. Response of the soil tunnel system for the Uttarkashi earthquake (1991) has been found out in the form of maximum forces induced in the RC liner of the tunnel, displacement, induced acceleration and stresses. The results have been compared with the available closed-form solutions. Parametric studies by considering different parameters such as effect of contraction (volume loss), influence of boundary conditions and damping, effect of interface condition between soil and tunnel, effect of displacement time history and effect of a nearby building have also been conducted. Forces in RC liners and stress concentration obtained in the present study are well-matched to those obtained by available closed formed solutions. The vertical stress concentration and volume loss depend upon the soil medium's constitutive behavior. The section under consideration was safe against the 1991 Uttarkashi earthquake. It can also be observed that, due to the presence of the building, the axial force and bending moment increased in tunnel’s liner, and the value of all three forces reduced as the position of the building was away from the tunnel. Shear force and bending moment were maximum for full slip condition between soil and tunnel lining however the effect of the interface condition on the displacement was negligible after a certain value of the interface condition.
Rock Mechanics
A. Alikhani; M. Taheri Moghadder; H. Mohammadi
Abstract
One of the most effective parameters in economics of open-pit mines is the pit slope angle, so that the slope angle more than the optimum value increases the probability of a large failure in the pit wall and the slope angle less than the optimum value leads to increasing stripping ratio and reducing ...
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One of the most effective parameters in economics of open-pit mines is the pit slope angle, so that the slope angle more than the optimum value increases the probability of a large failure in the pit wall and the slope angle less than the optimum value leads to increasing stripping ratio and reducing net present value of mine. Therefore, in this paper, considering the limit equilibrium methods of modified Bishop and modified Janbu and numerical models of the slope stability analysis, the effect of overall slope angle on the Economics of open pit mines was investigated. In addition, it was shown that selecting the overall slope angle less than the optimum value leads to reducing the depth of open-pit mining (the ultimate pit depth) and consequently, reducing the net present value of mine. Finally, in homogenous and Isotropic media, the results of Bishop and Janbu and numerical modeling are close together.
Omid Saeidi; Ahmad Ramezanzadeh; Farhang Sereshki; Seyed Mohammad Esmaeil Jalali
Abstract
This study aims at presenting a numerical model for predicting grout flow and penetration length into the jointed rock mass using Universal Distinct Element Code (UDEC). The numerical model is validated using practical data and analytical method for grouting process. Input data for the modeling, including ...
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This study aims at presenting a numerical model for predicting grout flow and penetration length into the jointed rock mass using Universal Distinct Element Code (UDEC). The numerical model is validated using practical data and analytical method for grouting process. Input data for the modeling, including geomechanical parameters along with grout properties, were obtained from a case study. The effect of rock mass properties such as joint hydraulic aperture, spacing, trace length, orientation and grout properties as yield stress and water to cement, w/c ratio was considered on grout flow rate and penetration length. To illustrate the effect of aforementioned properties, models were constructed with dimensions of 40×20m. A vertical borehole with diameter of 60mm and 10m depth was drilled in a jointed rock media. The results were in a good agreement with analytical method. It was observed that by increasing joint hydraulic aperture, grouting flow increases using a power law function. The optimum grout penetration observed with joint sets intersection of 40°-60° as experienced in practice. With an increase in joint spacing grout penetration increases around borehole when spacing exceeds two meters it decreases, gradually.
