TUNNELING & UNDERGROUND SPACE ENGINEERING
Year:2019 | Volume:8 | Issue:1 |Papers Count:6

Summary The phenomenon of TBM jamming is one of the most hazards in full mechanized tunneling projects that should be considered at design time. This paper investigates the jamming possibility around full face excavation machine in Qom metro project. To achieve this purpose, different solution methods including empirical relations, analytical solutions and numerical modeling have been used. Since the excavation environment is continuous, to analyze the tunnel based on the numerical method, the Plaxis 3D software is used. Based on the results, in some areas, there are face instability and also the possibility of TBM jamming. It should be mentioned that the obtained results are function of the analysis method so that the calculated support pressure in numerical modellings is larger than its value in the other methods. Introduction Tunneling in weak and low resistance environments presents significant design challenges. As the resistance parameters of these media are low, the displacement analysis and the assessment of the non-elastic zone characteristics are very important, especially in areas where there are numerous high-rise buildings. Furthermore, the tunneling-induced ground displacement has a great influence on existing urban structures, and the evaluation of displacements (in the design stage) is a difficult subject, which many tunneling engineers have encountered. In these media, tunneling by TBM is an effective method to control the ground displacements. However, when a large time dependent deformation occurs around the tunnel, the ground pressure imposed on TBM shield could cause TBM jamming. Therefore, the jamming prediction in full mechanized tunneling projects is an essential part of tunnel design and machine selection. Methodology and Approaches The Qom metro project is one of important urban tunneling projects in Iran. In this project, about 10 kilometers of the entire tunnel are excavated by an earth pressure balance (EPB) shield TBM. The main purpose of this paper is to investigate the jamming possibility surrounding shield of EPB-TBM in the Qom metro project. The pressure required for the face stability was calculated using empirical, analytical and numerical methods. The numerical modeling in this study is carried out using Plaxis 3D software. Moreover, a comparison is made between the results of different methods. Finally, the effect of various parameters on the face stability and jamming possibility is evaluated via sensitivity analysis carried out in this research work. Results and Conclusions According to the results, when the ratio of overburden to tunnel diameter is more than 2, the results of the analytical and numerical methods are similar. The differences in results are due to differences in the parameters and the behavioral model used in the numerical modeling and analytical methods. For example, in some analytical methods, for excavation medium, the elastic behavior is considered, while in three-dimensional (3D) numerical modeling, several non-elastic behaviors could be considered.

Summary Computer method is one of the ventilation network design methods in underground excavations. Computer method has been designed based on mathematical approximate methods. Methods such as Newton-Raphson method, Hardy Cross method and its modified versions, critical path, linear analysis, non-linear programming and optimization techniques are considered as some mathematical approximate methods. Newton-Raphson method is one of the methods of solving nonlinear equations in numerical calculations. This method is designed based on the definition of derivative and its correction. Using Newton-Raphson method for the analysis of ventilation networks in underground excavations has been common. However, so far, perfect investigation of this method has not been carried out. The purpose of this paper is to investigate Newton-Raphson method and its improvement in the analysis of ventilation networks in underground excavations. The analysis indicates that this method in some models is unable to find the final true answer because instead of convergence, it diverges. Thus, the improvement of this method seems to be necessary. Introduction Ventilation design of underground excavations is done based on preparing underground excavation map, identification of branches and injunctions in ventilation network, calculation of mine resistance for any of branches, calculation of air flow quantity for any of branches, calculation of pressure loss for any of branches, calculation of natural ventilation, network adjustment, selection of regulator doors and selection of main fans. Various methods have been presented such a manual and computer methods for the analysis of ventilation networks of underground excavations. The choice of analysis method depends on the purpose of ventilation network analysis. Methodology and Approaches One of the methods for solving nonlinear equations in numerical calculations is Newton-Raphson method. This method is designed based on the definition of derivative and its correction. In this method, the error amount of the initial guess is calculated for purpose function, and then, the initial guess is corrected. In this method, based on the equation and injunction rules, supposition flow quantity for any of branches. is supposed. Based on the ventilation network fans and mathematical approximate equations, the error of any ring in the ventilation network is calculated, and then, supposition flow quantity is corrected. Based on the mathematical equations, correction operations of air flow quantity are repeated until the calculation accuracy becomes equal to or smaller than the calculation error. Results and Conclusions Newton-Raphson method is one of solution methods in ventilation networks analysis. Convergence to the final solution in this method depends on supposition flow quantity, the direction of supposition flow and the arrangement of ring selection. If the direction of the hypothetical flow in the network is in accordance with the actual flow direction, the fastest method for reaching the final solution in the analysis of underground ventilation networks will be the use of Newton-Raphson method. However, if the direction of the hypothetical flow in the network is not in accordance with the actual flow direction, the validation of this method will indicate that this method in some models becomes divergent. Therefore, improvement of Newton-Raphson method is necessary. The improvement of Newton-Raphson method in this paper is made in two stages. The first stage is the identification of negative flow intensity, and then, the flow direction is reversed. In the second stage, the correction of the equation is performed, and then, the calculations are repeated.

Summary Induced ground surface settlement due to tunneling causes damages to the adjacent structures. Relative stiffness approach is a well-known method of estimation of these probable damages based on soil to building stiffness ratio. Importance of calculation of the structural stiffness in an accurate way necessitates a comparison between the results of different available methods. In this study, the numerical analysis is performed to recognize the most suitable method of the calculation of the bending stiffness of the buildings. The obtained modification factors are then plotted versus the calculated relative stiffness. The numerical results show that the amounts of the settlement that are underestimated by conventional methods. Therefore, in this paper a correction factor is proposed to improve previous modification factors. The proposed approach maintains the simplicity in the calculation process besides of its more accurate results. Introduction In conventional methods, the ground settlement of the greenfield condition is evaluated, and then, applied to the investigated building. The induced deformation to the building is affected by its stiffness. Therefore, estimating an accurate value of the stiffness leads to the results for better understanding of the response of the building. Various approaches such as the parallel axes, Lambe and Meyerhof methods are available to calculate the bending stiffness of a building. However, selection of an efficient method for calculation of the building stiffness is important. Methodology and Approaches The problem is analyzed by finite element method based PLAXIS2D software considering different geometries. It includes buildings with variable numbers of stories and different widths of footings. Settlement trough is obtained for each condition and bending stiffness of each building is calculated based on the length of the hogging and the sagging part of the building. The deflection ratio and the modification factors are then calculated. The obtained modification factors versus the relative stiffness are plotted in a semi-logarithmic domain. Results and Conclusions The obtained results from this research work indicate that the conventional methods of estimation of the building deformation due to tunneling predict underestimated values in the sagging part of the settlement where the majority of the building is damaged. Therefore, this study has been made to look into this problem by introducing a new correction factor. By using this factor, the damage can accurately be determined.

Summary Kerman water transfer tunnel with north-south direction has a length of 37. 5 kilometers and a diameter of 3. 8 meters has been established with the aim of long-term water supply in Kerman City. Environmental impact of this tunnel is assessed using RIAM matrix approach in two ways. After examining the environmental effects of the tunnel, the most positive effects of the plan for exploitation, as well as the negative impacts on the construction phase are determined. Introduction Kerman water transfer tunnel with north-south direction and a length of 37. 5 kilometers and a diameter of 3. 8 meters is very important for the purpose of long-term water supply in Kerman City. Due to the length of the tunnel track and using TBM for the tunnel excavation, and considering the negative effects of the tunnel project, it is necessary to assess the environmental impacts of the project. Methodology and Approaches In this study, to assess the environmental impacts of Kerman water transfer tunnel, the RIAM matrix approach is used in two ways and also, the possibility of non-implementation of the project in two phases, as well as the effects of its construction and operation from the physical, chemical, biological, economic and social-cultural aspects are investigated. Results and Conclusions After examining the environmental effects of the tunnel, the most positive effects of the plan for exploitation, as well as the negative impacts on the construction phase are determined, and then, a program is implemented for the management and environmental monitoring of the tunnel by considering the environmental and the positive effects in short and long terms.

Summary Urban subways in the ground would change its seismic movements. Designing ground surface structure in far filed is related to the horizontal component of acceleration at the ground surface in that area. Therefore, an attempt has been made in this study to change the frequency of soil-tunnel systems and to calculate the maximum horizontal acceleration of the ground surface due to tunnel presence through changing in tunnel placement depth, its diameter and its lining thickness as well as changing the soil properties. The maximum horizontal acceleration of the ground surface has been calculated in the presence of the tunnel for soil type 4 based on code 2800. The relationship between the maximum horizontal acceleration of the ground surface and the frequency of the soil-tunnel systems will result in the production of a horizontal acceleration spectrum. In the frequency range studied, spectral accelerations in models without a tunnel have mainly higher values compared to those models that have a tunnel buried in the soil. Amplification and deamplification of the ground surface acceleration is dependent on the period of soil-tunnel systems, the properties of the model under study and the position of the point studied at the ground surface. Introduction 9 acceleration records of known influential earthquakes, 33 models (in presence of tunnel) and 7 models (in absence of tunnel) have been used in this study. Overall, about 360 nonlinear dynamic analyses have been carried out. These analyses have been made for multilayered soil while the nonlinear effects of the soil and its interaction with the surrounding structures have been considered. Methodology and Approaches This study has been conducted on a Delhi subway tunnel. ANSYS and Plaxis2D software packages have been used for the study. The ANSYS software has been used for modal analysis, obtaining the frequencies and mode shape of the soil-tunnel systems, while the Plaxis2D software has been used to analyze the time history and obtaining the acceleration values of key points of the model. Elasto-plastic Moher-Coulomb model has also been used to model the soil. Results and Conclusions In most cases (11 out of 14 cases), amplification of ground acceleration is observed at a depth of 20 m. 9 of the 14 ground acceleration amplification are related to a tunnel with a smaller radius (3. 13 m). Whatever the tunnel center image is taken away from the ground surface, we will have higher number of points in which acceleration amplification of the ground surface occurs.

Summary In this paper, reliability analysis is achieved for composite supports consisting of steel sets and shotcrete in tunnels. Appropriate distribution functions for spacing between steel frames and shotcrete thicknesses in tunnels are obtained from the statistical data collected from a recent tunnel project in north of Iran. The distribution functions are then utilized for reliability analysis of the supports using Monte Carlo technique to simulate shotcrete thickness and steel set intervals. The results indicates that effect of imperfections and deviations of shotcrete thickness should be considered in the determination of safety factor for design of temporary composite supports. Introduction Construction of tunnels has been increasing in recent years due to development of infrastructures such as highways, underground, railways and passive defense facilities. In order to excavate tunnels, both traditional drilling and blasting methods, as well as modern techniques such as TBMs (tunnel boring machines) might be used. After excavation, support systems need to be employed to make the tunnel stable. There are several approaches to support tunnels. Steel frames combined with shotcrete are usually utilized as primary support system in loose ground conditions that is the case studied in this research. Quick installations of steel frames and rough boundaries of the tunnel due to excavation circumstances lead to different shotcrete thicknesses and different spacings between steel sets. As a result, the thickness of shotcrete and spacing between steel sets can be considered as random variables. Therefore, in this paper, different failure probability is derived for different safety factors, which are used for design of steel sets and shotcrete composite support system. Methodology and Approaches For this study, different distribution functions have been utilized to fit the data. Each function is evaluated by three well known methods called Chi-squared, Kolmogorov-Smirnov and Anderson-Darling methods. According to the results obtained from all the three methods, the generalized extreme value (GEV) distribution function is recommended for the thickness of shotcrete and the Wakeby distribution function is suggested for the spacing between the steel sets. The selected distribution functions are then utilized to simulate the thickness of shotcrete and the spacings between steel sets. The Monte Carlo technique is used to evaluate the possibility of failure for various circumstances of different shotcrete thicknesses and steel sets intervals. Results and Conclusions The results indicates that effect of deviations in shotcrete thickness should be considered to determine safety factor for design of composite sections of steel sets and shotcrete. Therefore, in this paper, safety factors are determined to reach several certain amounts of failure probabilities.