Studies On Risk Evaluation And Control Measures Of Metro Shield Construction In Soft Soil

With the rapid development of China’s economy and the acceleration of urbanization process, a number of the city traffic increasing, city traffic congestion becomes more and more serious. Therefore, building urban metro has become the best way to solve the urban traffic and maintaining the sustainable development of city.In metro construction, shield tunnel construction, compared with other method, has its unique advantages that has been widely used in many domestic metro. Metro shield is a complicated engineering system, there are uncertainty, complexity and unpredictability factors exist in the process of construction, which make the shield construction have large potential risks. This paper is concentrate on studied the control method and the risk assessment of soft soil layer of metro shield construction, the main research contents and results are as follows:(1)Based on overseas currently researches situation of risk management and the theory of metro shield construction technology, the paper summed up those problems existing in the researches and come up with the contents and technical route. This paper also introduces the contents of the metro shield tunnel construction risk management, summarizing the methods of the risk identification, risk assessment and risk control, finally, putting forward the suitable method for metro shield tunnel construction risk management.(2)This paper analyzed the typical accidents of metro shield tunnel construction and factors which has great influence toward soft soil layer of metro shield construction, introduced the extenics theory into the metro shield construction risk assessment, in combination with simple correlation function method to calculate the evaluation index weight value and extension risk assessment model is established, the Ningbo metro line 2 Lishe Airport Station~Lishe Xincun Station shield interval on the risk assessment, evaluation results are obtained.(3)Through the metro shield construction risk identification and risk assessment results, this paper bring up the core of risk management system, the "three figures and 4 tables" in shield construction process. The management system of "three figures and 4 tables" which clarify the responsibilities of the different cooperation parties and the implementation of responsibility system of on-site safety management, selecting the shield tail clearance, the design axis deviation, tube one-sided normals and shield machine axis angle as the key parameters so that forming the key parameters of shield machine control table, realizing the layered management and fining management of progressive control and remote monitoring.(4)This paper choose the dangerous old houses and river section which continuous wear in shield to studies the key construction technology. The essay obtained the risk factors of dangerous old houses and river section which continuous wear by analyzing those program geology and location of cross section. When shield continuous across a dilapidated house and rivers, people should adjust the construction parameters so that to maintaining the balance and continuity of shield construction. During the shield tunnel construction process, people also should combines the condition of shield construction environment and take the monitoring points toward the surface subsidence, implementing the "three figures and 4 tables" management mean to analyze the key parameters of shield construction which provide monitoring data dynamic that used to guide the construction, so as to adjust the parameters of shield construction and to ensure the safety of the shield construction. The monitoring results show that the surface subsidence do not have great effect on the safety of the surrounding environment, which caused by shield construction in less than 10 mm.