نشریه مهندسی تونل و فضاهای زیرزمینی
سال هشتم شماره 2 (زمستان 1398)

Summary Metropolitan underground tunnels is increasingly used these days. Besides, Iran has strategic importance in the Middle East meanwhile risking always military attacks of hegemonic countries and local terroristic activities. Concerning the mentioned points, it is crucial to investigate and analyze such structures under explosive loadings. This research focuses on the most critical scenario of damage distribution in the tunnel covering cause by TNT explosion. Moreover, the effects of soil overburden height as well as the amount of explosive material is studied on the maximum stresses and deformations created in the covering of twin tunnels under 4 explosive loadings of 15, 30, 45 and 60 Kg TNT. At the end, the effect of soft soil rehabilitation is assessed on the improvement of tunnels covering response under explosive loading. Introduction Chio et.al (2006) studied the response of underground structures subjected to the explosion through nonlinear analysis [5]. In 2006, Gui et. al investigated the effects of ground surface explosion on the tunnel of Taipei Shongsan airport. Two dimensional solution of the problem by Gui et. al has been in the line of its simplification [6]. Lui has focused on the effects of explosion in New York subway. The conducted numerical investigations have been mainly two dimensional. The researchers mostly believe that plane strain assumption in the modeling is dramatically conservative in the explosion issue. Methodology and Approaches In this research, soil and tunnel have been subjected to the inside ground explosive loading in tri- dimensional form using ABAQUS6-11-1 finite element software. The explosive loading has been estimated through empirical relations of compression applied to the underground structure due to the explosion. Besides, the soil has been simulated by Druker Prager and the tunnel covering by Concrete Damage plasticity behavior models. Here, the effects of different parameters are investigated on the responses of twin tunnels under explosive loadings. Results and Conclusions The brief results of this investigation are as follows: 1- Increasing in the overburden height will cause the reduction of stresses and deformations in the covering of tunnels; 2- The most critical scenario of damage distribution in the tunnel section is in the overburden height of 10m under 60Kg TNT of explosive loading; the highest width of created crack is 91mm. the highest the height of soil overburden is, the more the created damage is in the tunnels covering under internal explosion; 3- The strength and stiffness of the ground should be rehabilitated in the soft soil surrounding the tunnel. The maximum stress is reduced for 44% with increasing the thickness of tunnel surrounding soil for 1m; 4- The maximum stress created in the tunnels covering is reduced by increasing the stiffness of soil. This reduction in the stress response is stopped in the status of increasing the thickness from 3m to 4m. 5- The stresses created in the tunnels covering are reduced with increasing the soil stiffness. The maximum stress remains approximately in a constant range in different values of soil strength.

In the last decade, the block caving method has been being proposed to use as the best option for large-scale and low grade deposits in depths. This method is one of the most important methods which can compete from productivity point of view with surface mining methods. However, the accurate understanding of geotechnical problems in caving have been asserted by plenty of operational experience in large block caving mines. In addition, the ability of caving (cavability of ore and cap rock) is the most important factor to apply this technique. Also underestimate of this variable not only can cause many problems in processing but also in the worst case tend to fail the project. Analysis of regions duo undercutting to ensure the accuracy of predicted caving is very useful in various mines. Mechanical and geometry properties of joints by using jointed material inserted in the model. The results proved that not only by increasing strength parameters of the rock mass height of Yield zone was decreased, but also by increasing dip angle of the joint the height of Yield zone was reduced. In addition, the results showed that the more dip angle of joint height we have, the less yield zone we have. Also the Joint friction angle has the most effective on height of Yield zone. In fact rock mass with dip of joints 20 degrees has the highest height of Yielding zone. This reduction had occurred in the range of 30 to 45 degrees by low gradient and in the range of 45 to 80 by a high gradient.

Excavation of tunnels and construction of underground safe facilities are always faced with numerous challenges and problems that often hinder or stop the work progress. Excavation of loose media is such a challenge which creates a special structure in weak strata. Therefore, in such conditions, it is important to be aware of proper method for improving the condition of the ground and the excavation methods in order to achieve the maximum safety and operational efficiency. The present study aimed to investigate excavation method of Glass water transmission tunnel in the alluvial section of the path.The present study aimed to investigate excavation method of Glass water transmission tunnel in the alluvial section of the path. The stability of this tunnel has been investigated during the implementation of NATM, EPB, TBM and ADECO-RS excavation methods. Studies have shown that the study field is a high-risk area. Excavation of the tunnel was studied through the ADECO-RS method. The tunnel and the project conditions were designed using the FLAC3D software. With regard to the pre-constraints imposed on the face, the obtained displacements were within an acceptable range. On the other hand, the predicted support systems in the tunnel have the capacity to withstand the loads and moments. Therefore, implementation of the ADECO-RS method is recommended in deep alluvial condition.

The optimal distribution of air in mining operations can be called the most important executive solution to reduce the operating and capital cost of the ventilation system that causes by choosing the correct location and characteristics of the fans for the actual and adequate distribution of air flow in The network. Due to the multiplicity of parameters affecting the performance of the active ventilation system and its various components, achieving the optimum network parameters is time-consuming. Applying Metaheuristic techniques can help solve problems quickly and find optimal values of ventilation network. The ventilation network simulation was performed in the two-dimensional implementation of the eastern Kalariz coal mine, identifying 43 nodes, 61 branches and 22 network loops. Then values of the intersection matrix and the fundamental matrix of the loop were identified. After simulation of the current design with the Ventsim software, the air flow rate in some of branches was less than the required level to establish the required minimum air flow rate. Therefore, the optimization of air distribution in the Kalariz coal mine was conducted in two separate conditions including the current conditions of the mine and supplement of minimum air flow intensity in all branches of the network. For network modeling, the semi-controlled flow type II was determined. Then the coding of the objective function in Matlab R2014 software was based on the minimization of energy consumption with regarding to flow rate and the pressure loses of the Kirchhoff's laws. Also the effect of the parameters of the genetic algorithm (mutation rate and crossover rate) along with population size on optimal response was investigated. The results of the implementation of the model indicate a decrease in energy consumption from 10054 to 10040 watts. In the second condition, the energy consumption increased to 13696 watts and the current intensity was 32 m3/second. This values due to the fact that there were more than 22 mining branches, which in the first case did not observe the minimum required air flow. The efficiency of the genetic algorithm was determined in the analysis of the optimal fan performance and the amount of pressure drop required for the regulator doors. Increasing the number of people to a certain degree increases the chances of achieving the optimal answer. As the coefficients of the crossover and mutation become larger, the accuracy of the calculation decreases and the time to reach the optimal response increases.

Summary In this paper, a novel method based on a semi-ring support has been developed and proposed to facilitate TBM passing the station and restarting the excavation. The results show that the proposed method can be safely used. Introduction Crossing of station is one of the most challenging problems in construction of metro lines. Given the difficulties and problems of using the push frame in the TBM passing station and restarting excavation, this study presents a method based on the use of segmental rings that has been developed for use in underground stations. Methodology and Approaches In this method, in order to create a support for applying the force of TBM thrust, a different pattern of the installation of the incomplete rings has been used so that in addition to utilizing the advantages of using the semi-ring support in such a way that any complete ring is not installed in the space of the station. The proposed pattern is such that three floor segments are used to a distance of about 5 to 6 rings to the end of station; so that TBM will pass through the length of the station. Thereafter, in a few rings, the number of segments increases to 4 and then 5 segments per ring until the cutter head reaches the end of the station. From this stage, the tunnel excavation continues with the installation of the semi-rings of 5 and 6 segments, until the boring machine is completely inserted into the tunnel so that the first complete ring is installed at the beginning of the tunnel. Results and Conclusions The results show that excavation can begin using the 5 and 6 segments, but semi-ring of 6 segments is somewhat superior to 5 segments. The proposed model has been evaluated at some stations of line 6 of Tehran metro and the results show that, in addition to the effectiveness of this method, any over-the-counter deviation has not occurred. Therefore, the proposed method can be safely used.

Longwall mining is one of the methods for coal extraction with high production efficiency, which requires a lot of initial investment to equip and prepare it. In the longwall mining process, with the advance of the coal face, the roof is damaged at the back of the coal face. To protect the main tunnels and access tunnels (Gaterodas) of the mine, the stresses created from the panel extraction are utilized in two ways. The first solution, which has the most important effect on the stability of the panel, is the placement of the chain pillar and the barrier pillar, and another way of installing the support in the main tunnels to control the tunnel convergence. Therefore, it is important to determine the width of the barrier pillar, which has the highest effect on mineral productivity and the least effect on the distribution of stress around the main tunnels. The main objective of this research is to obtain the appropriate width of the barrier pillar at the end of the E3 panel in the Tabas mechanized coal mine, so that the main tunnels of the mine have the lowest convergence. The FLAC3D software was used for numerical modeling. The results of various numerical models of the advancing coal face shows that width of the barrier pillar has an effect on the distribution of stress. Finally the result shows that the suitable width of the barrier pillar is 80 meters. Also, the result of economical investigation shows that 80 m pillar width causes more than 6000 tons of coal to be extracted.