| Since the 21 st century,the construction of underground projects in China has developed rapidly,accidents caused by metro construction frequently occur.The intrinsic dynamic nature and uncertainty along with the shield tunneling,make the evolution of the accidents complicated with multi-source risk factors.Therefore,it is of great theoretical and practical significance to explore the law of evolution mechanism from safety risk factors to the final accidents during the shield tunneling process.Firstly,we analyzed the working process and key points of operation during the shield tunnel construction,and established a risk evaluation index system based on the risk mechanism of metro construction.A method of integrating exploratory factor analysis(EFA)with structural equation model(SEM)was proposed to investigate the safety risk change law of the whole process of metro shield construction from the subjective point of view.Subsequently,the iterative self-organizing data(ISODATA)clustering algorithm was employed to analyze the incident report of the metro shield construction,which indicated the effectiveness of safety risk “bathtub” curve law from the objective point of view,and revealed that inrushing and excessive ground settlement were the main accident types.Finally,we constructed a fine simulation model by ABAQUS,and analyzed the safety risk evolution process of the inrush accidents in the metro shield construction.We integrated the Bow-tie analysis(BTA)and the Fuzzy-Bayesian Network(FBN)to analyze and evaluate safety risk of the excessive surface settlement in the metro shield construction dynamically.Combining the results of ABAQUS simulation and the BTA-FBN probability analysis,the corresponding safety management measures were formulated,which can effectively assist the control of safety risk in metro construction.The main contents of this thesis are as follows:(1)To reduce the cognition uncertainty about tunneling induced safety risk due to the lack of kowledge,the working flow and key points of operation during the whole metro shield construction process were analyzed,and a safety risk evaluation index system was established.In the light of the safety risk assessment index system,a safety risk survey questionnaire for the whole process of metro shield construction was formed.According to the questionnaire survey results of the subjective experience of the site workers,by integrating the exploratory factor analysis(EFA)with the structural equation model(SEM),we established the safety risk "bathtub" curve indicating the key stages with high safety risk and the leading risk factors in the whole process of metro shield construction,which provide a basic framework for the clustering research of safety shields based on ISODATA.(2)On the basis of the analysis of the change of the safety risk in the whole process of the metro construction,the ISODATA clustering algorithm was used to study the metro shield construction safety events(i.e.near-miss and accidents).The law of the "bathtub" curve of the safety risk in the whole process of the metro construction was fitted,which verified the safety risk change rule in the whole process of metro construction based on EFA-SEM from an objective point of view.In addition,through cluster analysis of metro construction accidents,the main types of accidents were determined,which is the research object of the subsequent accident evolution mechanism analysis.Firstly,to cover as much information as possible,the near-misses with high frequency and low severity were also included in database.Secondly,according to the basic framework of the construction phase and risk factors extracted by the EFA-SEM model,243 collected safety events were analyzed,to establish a structured database with the incidents categories and variables contained.Finally,the cluster was established by ISODATA clustering algorithm,and the distribution of the overall database variables were analyzed.The safety risk “bathtub” curve of the whole process of metro shield construction was obtained.Through the comparison of clusters and database,as well as the severity level of various consequences,the result of the risk degree of the clusters was obtained,thus confirming the main types of the metro construction accident are inrushing and excessive surface settlement.(3)According to the conclusion that the main type of metro construction is the inrushing,the evolution mechanism of the inrush accidents in metro construction was explored.The shield tunneling of the XW section was selected as a study object in this thesis.A fine hybrid model of the inrush accident in the construction of metro shield was established based on the 3D nonlinear contact theory,with in consideration of the interaction between soil and water,the lining discontinuity of shield tunnel and the interactions between tunnel segments,grouting layer and surrounding rock.The variation of water head difference that reflects the dynamic evolution of water grushing flow,was simulated to investigate their effects on the mechanical and deformation properties of the segments and joints in the shield construction.By comparing and analyzing the results of the inrush accident model in different construction stages,it was verified that the launchingarrival was the key stage of construction safety risk control.Moreover,the safety measures of controlling the depth of the end reinforcement and the discharge of gushing water were put forward based on the calculation results of the inrush accident model.(4)According to the conclusion that the main types of metro construction accidents is the excessive surface settlement,the evolution mechanism of the excessive surface settlement accidents in metro shield construction was discussed.Based on the fuzzy statistic test theory,the "normal metro shield construction status" during the shield tunneling of the XW section was defined,which was used to extract the equipment failure probability from the noise reduction sample database.The probabilities of environment failure,operation error and multiple faults were evaluated by adopting improved expert weighted aggregation of fuzzy number triangles and trapezoidal numbers.A hybrid method combining bow analysis(BTA)and Fuzzy-Bayesian Network(FBN)was proposed,which map the Bowtie analysis into the Fuzzy Bayesian network to establish the causal network BTA-FBN evaluation model for the "normal metro shield construction state".By introducing three corresponding important measures,Birnbaum measure(BM),risk achievement worth(RAW),and Fussell-Vesely(FV),the key nodes of normal surface settlement model in "normal metro shield construction state" were identified.By comparing and analyzing the BTA-FBN model results of surface settlement at different stages of shield tunneling,it was verified that launching-arrival was the key stage of construction safety risk control.In addition,the relevant safety measures for excessive surface settlement were developed according to the identified key nodes of the accident dynamic evolution circumstance determined by BTA-FBN model. |
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