| With the rapid development of subway tunnel engineering, there are some characteristics in subway tunnel engineering compared with the ground engineering, such as complex geological conditions, technological diversification, confined space operations and so on, which make the risk management of construction more difficult. In addition, risk management theory is not yet perfect that leads to the tunnel construction accidents (disasters) occur frequently, so the risk of subway tunnel construction becomes the hot issue in the field of underground engineering. In order to control risk, the research on the risk theory becomes the primary task and the risk mechanism is the important content of risk theory, only when the risk mechanism is grasped, can the risk rules be grasped, so that to control the risk. Therefore, study on the risk mechanism of subway tunnel construction plays a key role in risk control.In order to study the risk mechanism and master the risk rule. First the idea of system dynamics is used to do the systemic analyze of the system, so as to understand the way of working of the elements in the subway tunnel system and the interactive relationship between the various elements under certain environmental conditions, to establish system dynamics model from the angle of mechanics and energy, to draw causal loop diagram and flow chart. According to the system dynamics model established, results of FLAC3D software simulation are embedded the system dynamics model, the Vensim software is used to simulate respectively from the angle of mechanics and energy, which can improve the accuracy of system dynamics model, to further expand the application range of the system dynamics. In order to measure the system risk, PHA method is used to evaluate the risk of subway tunnel construction, aiming at the defect which cannot ascertain risk level of PHA method quantitatively, combined the fuzzy set theory with rough set theory to establish risk assessment model based on variable precision rough fuzzy set to improve the method of risk classification of PHA, so that to reduce the subjectivity of the risk assessment process to realize quantitative PHA method. The research results of this dissertation are verified by practical examples. The concrete framework of the full dissertation is as follows:(1) The research status of tunnel construction risk theory, theory and application of system dynamics, risk simulation, risk assessment in and abroad are collated and summarized, and find out the existing problems.(2) In the analysis of subway tunnel system, in the first place, put forward the question of the subway tunnel system and confirm the purpose of the system analysis. The theory and method of system dynamics are used to analyse and study the subway tunnel system, the function and composition of the system. Based on the surrounding rock system as a key research object, the system dynamics models are established from the angle of mechanics and energy to analyze its causal relationship, and show the causal relationship graph to draw a flow chart according to it, finally find out the main influencing factors and various variables of the system stability.(3) The mechanics simulation result (FLAC3D software) is embedded into the system dynamics model based on mechanics, then the model is simulated (Vensim software). FLAC3D simulation software is used to simulate the influence law between different influential factors (surrounding rock condition, buried depth, section shape and size, support, construction and so on) and the vault settlement. On this basis, the equations of system dynamics model based on mechanics are estabished. The validity of the model will be tested. Finally, the model will be simulated by Vensim software.(4) The energy simulation result (FLAC3D software) is embedded into the system dynamics model based on energy, then the model is simulated (Vensim software).First of all, this paper analyzes energy risk theory, including risk and energy theory, the energy transfer, release, control mechanism. Basic theory analysis of risk and energy including relationship between risk and energy, the connotation of the subway tunnel construction risk, the relationship between risk constitution and key elements of risk, the advantages and disadvantages and the scope of application of the energy accidental release thory, the feasibility of the implementation of the energy accidental release theory, the risk mechanism based on energy principle. In the study of energy transfer mechanism, strain energy transfer process should be described and the energy transfer mechanism and the probability of strain energy transfer should be analyzed. In the study of energy release mechanism, the release conditions, release characteristics, release mechanism and possibility of strain energy should be analyzed. The control mechanism of strain energy should be analyzed by combining with the stress-strain curve.FLAC3D simulation software is used to simulate the influence law between different influential factors (surrounding rock condition, buried depth, section shape and size) and characteristic of accumulation and release of energy. On this basis, the equations of system dynamics model based on energy are estabished. The validity of the model will be tested. Finally, the model will be simulated by Vensim software.(5) PHA method is used to assess the risk of subway tunnel construction. Based on risk classification of PHA, combined the fuzzy set theory with rough set theory to establish risk assessment model based on variable precision rough fuzzy set to improve the method of risk classification of PHA. In the model establised, the risk is divided into the inherent risk and additional risk. The classification standard of inherent risk indexes are confirmed by using standard specification. The classification standards of additional risk indexes are confirmed by using the mechanics simulation results. Using the risk assessment model based on variable precision rough fuzzy set to study risk assessment of the sample, and to determine the risk level, the index weight is defined according to the measured values by using rough set theory, which can reduce the subjective influence to the assessment results, so as to enable the assessment results more objective, accurate.(6) Take the Tonghui door stop line tunnel of Chengdu Subway Line2project as an example, using the PHA method to assess the risk of it to verify the applicability of PHA method and the risk assessment model based on variable precision rough fuzzy set. |
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