TUNNELING & UNDERGROUND SPACE ENGINEERING
Year:2019 | Volume:8 | Issue:2 |Papers Count:6

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.

Summary In the last decade, block caving method have been proposed as the best option for extraction of large volume and low grad deposits at depth. This method is the only underground mining method, which is comparable to open pit mining in terms of cost and production capacity. However, operational experience in large block caving mines worldwide has proven the need for comprehensive understanding of the geotechnical processes in caving. The main condition for applicability of block caving method is the cavability of the ore body and surrounding rock. The inappropriate estimation of this variable can create problems in production and processing, or in the worst case, the project will fail. Analysis of the formed areas by caving is very useful for ensuring the accuracy of prediction of caving in different mines. In this study, using Abaqus 6. 12 software and Drucker-Prager's behavioral model, the effect of mechanical rock mass characteristics on yielded zone at the top of the undercut in the block caving method has been investigated. The mechanical and geometric properties of the joints have been introduced using jointed materials in the model. Introduction In general, cavability assessment methods and caving propagation are divided into three categories; Analytical, experimental and numerical. The most important experimental methods are Matews stability graph (1980), Laubschur graph (1990) and modified Matews stability graph by Madewsly (2002). In continuous numerical research (for example, Lorig et al. (2000), numerical modeling has been performed taking into account the continuous environment equivalent rock mass. In that research, the effect of joint properties on cavability has not been investigated. The discrete methods and software packages base on these methods like UDEC and 3DEC have limitedly been used for cavability assessment. The parameters considered in this paper include strength, stiffness, pre-mining stresses joint frequency, and top coal thickness. Their applications are mostly about the study of surface subsidence and stability of pillars. Methodology and Approaches The details, approach, tools, software, and the method of the research have clearly and briefly been explained in this paper. Results and Conclusions The results show that the height of yielded zone decreases with increasing strength parameters of the rock mass and joints. The friction angle of the joint has the greatest effect on the height of the yielded zone. The joints with dip of 20 degrees have highest height of yielded zone. As the dip of the joints increases, the height of the yielded zone decreases. This decrease occurs in the dip range of 30 to 45 degrees with very low gradient and in the dip range of 45 to 80, with a large gradient.

Summary Tunnel excavation in difficult geological conditions is one of the most important subjects in the construction of underground spaces. Geological conditions have a major impact on selection of tunnel excavation method as well as tunnel support method. The present study aims to investigate excavation method of glass water transmission tunnel in the alluvial section of the tunnel path. The stability of this tunnel has been investigated during the implementation of NATM, EPB, TBM and ADECO-RS excavation methods. The tunnel design and project conditions are implemented using FLAC3D software. Finally, among the methods used in this research, the ADECO-RS method has been selected as a suitable excavation method for the tunnels in deep alluvial environments, especially in the cases of glass projects. Introduction Construction of tunnels and underground structures are always faced with numerous challenges, including excavation of tunnels in alluvial conditions. Therefore, in such conditions, it is important to be aware of proper methods for improving the conditions of the ground and the excavation method in order to achieve the maximum safety and operational efficiency. Methodology and Approaches Today, many researchers use different numerical methods for analysis of tunnels and underground spaces. In this study, the tunnel design and project conditions are implemented using FLAC3D software. The analytical methods purposed by Jancsecz & Steiner and Kovari & Anognostou have been used to estimate face pressure in EPB tunneling method. Results and Conclusions In the case of EPB method, the stability of the tunnel face is evaluated using both numerical and analytical methods. The analytical methods purposed by Jancsecz & Steiner and Kovari & Anognostou have been used for this purpose. Due to good agreement between the results of numerical and analytical methods, especially the method purposed by Kovari & Anognostou, the face pressure equivalent to 13 bar has caused the control of instabilities in the present conditions of this project. In this regard, the thrust force of TBM in order to advance in deep alluvium conditions has been calculated and obtained as 105. 826 MN. In the case of NATM method, according to the displacements that occurred during the tunnel advance, the use of this method in the excavation the glass tunnel causes instability and therefore, the construction is stopped. Moreover, according to the applied pre-confinements in the front of face in ADECO-RS method, this method in the view point of tunnel stability acts better than NATM method. Analysis of the results indicates that the proposed support system has enough resistance versus destructive forces in the tunnel. Finally, considering the intensity of displacements created during the tunnel advance in the NATM method, the possible limitations of the EPB mechanized machines and suitable control of instability in the tunnel excavation using the ADECO-RS method as well as the efficiency of the temporary support system, the ADECO-RS method has been chosen Comparison of Excavation Methods Glass Tunnel Deep Alluvial Environments NATM Method EPB Method ADECO-RS Method as a suitable method for excavation of the glass tunnel.

In this research, an investigation on the genetic algorithm efficiency to determine the optimal air distribution in the ventilation networks and the optimal fan performance and required pressure drop for the regulator doors is carried out. The objective function of the model is the minimization of energy consumption. Introduction The optimal air distribution in mine ventilation networks is the most effective solution to reduce the operation and capital cost of the ventilation system that is achieved by choosing the correct allocation and characteristics of the ventilation fans. Due to the multiplicity and variations of ventilation networks parameters, achieving the optimum value is time-consuming. Applying metaheuristic techniques such as genetic algorithm (GA) can help to solve this problem and find optimal values of ventilation networks. Methodology and Approaches The simulation of Kalariz coal mine ventilation network was performed by considering 43 nodes, 61 branches and 22 loops. Then, values of the intersection and fundamental matrices of the loops were determined. After simulation of the current design using Ventsim software, the air flow rate in some branches was identified to be less than the minimum required level of air flow. Therefore, the optimization of air distribution by GA in the Kalariz coal mine was conducted in two separate conditions including the current conditions of the network and supplying the minimum standard air flow in all branches of the network. For the network modeling, the semi-controlled flow type II was determined. Then, implementation of mine ventilation constrains and objective function by considering the flow rate and the pressure losdes of the Kirchhoff's laws was performed in MATLAB R2014. software based on the minimization of energy consumption Moreover, the effect of the GA parameters (mutation rate and crossover rate) along with the population size on the optimal response was investigated. Results and Conclusions The implementation of the model in current condition of the ventilation network of Kalariz coal mine indicates a reduction in the energy consumption from 10054 to 10040 watts. In the second considered condition, the energy consumption increases to 13696 watts and the required air flow of 32 m3/second is obtained. These values are obtained due to increasing the flow rate of 22 branches while in the first case the minimum required air flow is not observed. Supply of the required air is provided by combining 2 existing VTS11 fans in the mine. The efficiency of the GA technique for the analysis of the optimal fan performance and the amount of pressure drop required for the regulator doors has been investigated. As the values of crossover and mutation rate become larger, the accuracy of the calculation decreases and the time to finding the optimal solution 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.