عنوان مقاله [English]
The aim of this paper is to redesign the main gate support system to control the floor heave in Tabas coal mine. This tunnel is located in the No.2 eastern panel of Parvadeh.1 Tabas coal mine (E2M.G). To reach this main, the amount of floor heave and the influence of face advance on the floor heave magnitude have been evaluated by FLAC3D software. The results have shown that the floor heave magnitude at control points, without considering the working face effect, is 45 cm, and when the distance between the panel working face and the control points is 5 meters, the floor heave magnitude will reach 145 cm. Finally, steel set (type IPB180) has been proposed as a support system. Furthermore, the excavation of main gate floor in curvilinear shape with 40 cm depth and the installation of 8 bolts in the floor have been suggested. In this condition, the amount of floor heave at a distance of 5 m in front of the panel working face decreases to lower than 20 cm.
One of the problems in mechanized longwall mining method is the existence of inappropriate ground condition such as swelling and squeezing in tail gate and main gate tunnels. Tunnel excavation in these grounds with presence of high induced stresses, which are applied on support system, will encounter many difficulties.
Methodology and Approaches
Numerical modeling has frequently been used in various fields of engineering and its results are usually accepted by various organizations. In this paper, three dimensional (3D) modeling of main gate tunnel of No. 2 eastern panel in Tabas coal mine was carried out using FLAC3D software. For modeling and determination of the amount of floor heave, Mohr - Coulomb and strain softening behavioral models were used and amount of floor heave was achieved in two states of regardless the face advancement and with considering the face advancement effect.
Results and Conclusions
The results of numerical modeling with face advancement indicate that vertical and horizontal stresses in the tunnel floor, respectively, become 2 to 2.5 and 1.5 to 2 times greater than the stresses caused by face advancement, and thus, it is one of the effective factors on amount of tunnel floor heave. Moreover, the numerical modeling results have shown that the best support system to control the tunnel floor heave is as follows:
- Using 4 steel bolts with 3 m length and 0.5 meter spacing in each row and 1 m row spacing in both sides of the tunnel roof
- Using 4 rock bolts with 7 m length and 0.5 meter spacing in each row and 1 m row spacing in the center of roof
- Using 4 fiber glass bolts with 4 m length and 0.5 meter spacing in each row and 1 m spacing in the right wall of the tunnel
- Using 4 fiber glass bolts with 4 m length and 0.5 meter spacing in each row and 1 m spacing in the left wall of the tunnel
- Using IBP180 steel set