Risk Evaluation And Control Of Rectangular Shield Tunnel

Rocks in this case are located in the land site of Ningbo stratigraphic region, mainly composed of cretaceous purple-red siltstones and partially effusive rocks in late Yanshannian. The quaternary strata are stable, ranging from Middle Pleistocene to Holocene(55m-100 m in thickness). The construction of Ningbo metro line shield tunnel will be at high risks, given the complex geological conditions, and complex construction procedures. In consideration of the serious wide-spread and profound social impact once the accident happens, large-amount of investment and construction required, complicated construction procedures, and the high risks involved, the risk pre-evaluation, analysis, and precautions before the construction of metro line shield tunnel would be necessary and are expected to provide strong support for the subsequent construction. Thus, the case study of risk evaluation and control of the Ningbo rectangular shield tunnel presented below would be very meaningful.Main scope of this case study includes:Summarize the existing problems in the current studies of domestic and international shield tunnel construction. Propose the study contents and technical solutions based on current risk analysis and evaluation method.Start from the basic concept of risk and construction risk, introduce the risk types and its four characteristics(damage, uncertainty, complexity, and periodicity), explore the risk formation mechanism from aspects such as risk-nurturing environment, risk factors, risk accidents, risk bearer, vulnerability, risk loss, risk benefit, and risk cost, and summarize the related methodology of risk management.Establish the fuzzy integrated evaluation system of shield tunnel construction risk, use AHP to allocate the weight for risk factors in this case--- Ningbo metro line 3 phase I underground TJ3111 civil work and rectangular shield tunnel construction(two stations and two intervals: Huangjiacun station, chenpodu station-huangjiacun station interval, chenpodu station, jiangshan-shield interval)---and apply fuzzy integrated evaluation system to assess the risk factors and overall construction risk levels in the Ningbo metro line shield tunnel construction.Assess the risks during the shield tunneling break-in and break-out stage, and breakthrough the special sections, and the technical solution for segment assembling risk, based on the risk evaluation and comparison analysis of both rectangular and cylinder shields, and propose quality assurance measures for Ningbo metro line rectangular shield tunneling construction.