岩石隧道施工风险评估方法应用研究
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摘要
近年来隧道产业的发展一直伴随着损失与事故。这些事故的发生归因于下列因素：复杂的地质条件,错误的设计以及不合理的施工方式。正是缘于隧道施工的复杂性,以及期间的巨大花费,对每个阶段(从项目的招标到具体的正确施工)进行风险评估已被广为认同。
隧道工程中潜在着许多风险。例如：凿隧道时遇到流动和含水的断裂带、在流动或块状地面上隧道壁不稳定、坚硬的或者腐蚀性的岩石断面以及收敛的岩石断面等等,这些都是风险存在的主要原因。近年来采用的施工方法是机械化掘进,这种方式最主要的问题是选取最合适的隧道掘进机以及在每种地质条件下的绩效预期与评估。以韩国青年洞隧道的建设为例,它就进行了详细的评估来确定哪种方法用于隧道施工是最好的。我们根据这项研究来探究导致中国工程安全管理薄弱的因素,得到的结论是：影响安全绩效的主要因素包括“高层领导者安全意思薄弱”、“缺乏训练”、“项目经理安全意识薄弱”“不愿意进行安全投资”以及“行动鲁莽”。工程风险被划分为三类：建设融资风险,建设工期风险以及施工设计风险,然后鉴于职能部门中合同方的不同,我们再将这些风险细分,因为这些合同方在设计、发展以及施工中发现风险与找到解决方案的过程中所起的作用不同。
从2006年4月25日召开的首尔ITA会议得来的数据来看,从1994年到2005年总共有19个主要的隧道工程因为火灾、地震坍塌造成了高达6亿美元的经济损失。这些工程包括：大贝尔特环线(丹麦),慕尼黑地铁(德国),西斯罗机场快线(国际),洛杉矶地铁(美国),台北地铁(台湾),赫尔——约克郡隧道(英国),博洛尼亚——佛罗伦萨(意大利),安纳托利亚高速公路(土耳其),韩国大邱地铁,台湾高速铁路,SOCATOP巴黎,上海地铁(中国),巴萨罗纳地铁(西班牙),新加坡地铁(新加坡),洛桑地铁(瑞士),Lane Cove隧道(悉尼),高雄地铁(台湾)
几位研究人员运用了一些理论来分析工程中所涉及的风险,运用函数的方法分析评价建筑行业中的风险。这包括统计和定性的方法。统计方法：在这个方法中,有两个预先的要求必须完成。这两个要求是指可用的数据量必须充分,并且这些可用的数据必须从与将要评估的项目的情况相同或者非常类似的条件中得来。经验数据的统计分析在研究技术风险中尤其可行。但是,隧道工程就像其他的工程一样,只有部分环节有经验数据,识别环节尤其缺乏经验数据,所以一个充足的、可靠地数据库并不是总是存在的。通常情况下,工程项目中的计划与控制系统并没有就风险的影响进行充分的分析与评估。定性的方法：根据弗兰卡的理论,即在客观的数据不可用,但我们仍然必须对风险进行定量分析与评估时,一种方法便是进行定性分析并衡量这些通过评估事故发生的可能性以及其造成的损失而主观判断出来的风险。因此,专家讨论被用来评估项目中的风险。以下是专家评估与管理风险的一些方法：德尔菲法、(Post mortem analysis)。德尔菲法是指大量的专家就一些环节进行专家评估。这其实就如在专家中实行头脑风暴法,来确定与施工相关的风险并找到与之对应的解决方法。终止后分析方法可以被充分的运用到风险的辨别和评估当中。(Post mortem analysis)分析的结果被运用于项目的错误与故障的鉴别当中。这些结果有助于为将来的项目进行风险归类。此外,终止后分析方法同样有助于组织内的学习。还有一些其他的经常使用的方法包括KJ法以及根本原因分析法。KJ法是以日本的人文学家喜田二郎的名字来命名的,他帮助我们更好的了解问题的内在联系。根本原因分析法也叫做石川图或鱼骨图,它被用来对一个问题的所有原因进行系统定位。
隧道施工和规划向所有的部门提出了挑战,因为隧道工程一个昂贵的、其实施的每个阶段都有许多风险存在的地下工程。高效的施工规划是指以现有的资料为基础,优化挖掘隧道的顺序并决定初期支护的方法。一些项目表明仅仅选择挖掘及支撑隧道的方法是不够的,尤其在我们要考虑到项目的完成成本与其预期成本时是不够得。因此,隧道成本估算仍旧存在困难。这是因为现有的评估方法不能将与隧道施工相关的效果显著的因素体现出来。例如,地质不确定性,隧道施工过程中生产效率的不稳定性,隧道运营动态和承包商对于风险的敏锐度。
隧道设计不同于其他传统市政工程(诸如房屋建筑与桥梁工程)的设计。在传统工程的设计上,应当首先确定外部荷载对结构的影响,选择几何结构和能满足承载力、变现要求的建筑材料。但对于隧道工程的设计,设计者往往先解决复杂交错的岩石群和那些不能满足需要的地块。因为挖掘而使原始压力重新分配的外部压力并不能正确的确定下来。另外,地理结构的外形和地下水的可用性,它们对于隧道稳定性的影响更加显著与外部的荷载,而这些因素在传统的项目中是不用考虑的。此外,大部分的隧道穿过的地址条件都不同,因此我们很难确定沿隧道走线的地质情况。所以,隧道设计总是遭遇到地质情况不同寻常所带来的挑战。
大多数由岩石隧道设计师使用的隧道设计方法可以分为三种：经验法,分析法和测量物理法。而用于岩石掘进的两种主要方法是岩石隧道爆炸法和掘进机法。通常情况下,只选择这两种方法中的一种应用于特定项目的整个开挖。但是,为了使其更加经济,也可以在同一项目中同时采用多种方法。
风险评估是风险的识别和分析。在岩石掘进过程中存在多种可能的风险。包括有关工人和第三方的健康安全风险,工期延迟,资金损失以及环境的影响。然而这些风险与相关地质条件或者所应用的施工技术有关。据观察,大部分隧道是由于施工方法以及地质条件的选择不当才导致灾害性的后果,这最终会导致本公司或承包商的经济损失。风险评估存在于项目建设的每一个阶段：从投资阶段到项目实际建设阶段。早期的风险评估是项目决策和合同谈判的基础。
一般而言,一个项目的风险评估被定义为一个统一的程序,包括识别,分析,评估,监测以及相关的风险缓解。每个威胁的风险水平,取决于风险发生的概率和所要考虑的后果。对于与灾害有关的风险水平可以建立如下数学公式：风险水平=PH*CH
(PH指风险发生的概率,CH指相关的后果)
灾害发生的可能性可以被认为是可能的,偶然的或微乎其微的。尽管后果可能是灾难性的,评判的,严重的,微小的和微不足道的。
有关隧道建造业风险的判断与它的活动以及需要应用风险分析和管理技术的扩展方面有关。由此得出的结论是,风险评估在减少损失和提高盈利能力方面是必不可少的。隧道风险常常被看做是影响项目的费用目标,工期目标和质量目标的重要因素,建设中的风险评估和风险管理主要依靠直觉,判断和经验。由于缺乏知识以及对一些技术应用于建造业活动的适用性的怀疑,正式的风险评估和管理技术很少使用。实践准则是风险管理的最新进展,它是保证风险管理原则能应用于隧道和地铁项目的最实用的专业方法,并且能设法保证风险达到最低的合理水平。
过去几年由于隧道施工技术的不断改进,在建设中出现的风险也发生了变化。据观察,过去十年间,由于各种因素和经验的缺乏,在隧道工程中的风险变得特别高,并且恶化到一种无法维持的水平。因此,必须采取有效的风险评估方法。评审显示了在隧道施工中涉及的风险是如何演变的以及在如何避免增加风险上所取得的进步。由于风险评估涉及费用、工期和质量,成功应用于隧道开挖或建设项目的风险评估,给出了更清晰的了解项目目标、职责服务内容和项目可行性的机会,并且也为项目决策提供了基本的信息。
在本研究中,岩石掘进风险情况将分为自然风险,金融相关风险情况,设计相关风险情况和施工相关风险情况。一种情况是对于一个事件或一连串的行动或事件的综合描述。在这种情况下,风险情况是指发生并造成损害或构成对一个项目威胁的事件,我也将对在隧道工程中应用风险评估方法进行讨论。各种各样的风险评估方法被创建并用于岩石掘进的每一个阶段。本研究将展示各种方法在不同风险类别中的应用以及他们所使用的风险评估的工具。
本项研究将着重于考察评估风险的不同评估方法,指出个别评估方法的缺点,比较在隧道施工中应用的风险评估方法,选出较优方法。本研究采用风险评估软件(Palisade公司开发的@RISK软件)来运行一个模拟仿真项目的成本估算,并且采用基于主观判断的定量风险评估方法进行分析。从评估的结果在第五和六章来看,结果显示了蒙特卡罗模拟是如何给出一系列在任何特定项目中可能存在的意外事件和对于岩石掘进来说最合适的建造方法。
The tunneling industry in the recent past has been characterized with several losses and accidents. Several factors have been attributed as the reason for these occurrences. These factors range from geological conditions to the improper design and inappropriate construction methods. Due to the complexity and huge cost required in tunnel construction, risk assessment has been considered very needful in every stage of tunneling from project bidding to planning down to the construction proper.
There are many potential sources of risk in rock tunneling. Problems such as encountering fault zones with running and water bearing gouge, tunnel walls instabilities in running or blocky grounds, hard and abrasive rock sections and convergent tunnel sections are principal causes in risk occurrence. In recent times mechanized tunneling is selected as construction method, the most important problem is often related to selection of the most appropriate TBM and its performance estimation and prediction in each geotechnical conditions. For instance in the construction of the young dong tunnel construction in Korea a detailed assessment was carried out to ascertain which method is best to be used in the construction of the tunnel. According to the survey to examine the elements of poor construction safety management in China and as a result, identified the main factors affecting safety performance including "poor safety awareness of top management", "lack of training", "poor safety awareness of project managers", "reluctance to input resources to safety" and "reckless operation". Also construction risks were classified into three groups, i.e. construction finance, construction time and construction design, and addressed these risks in detail in light of the different contractual relationships existing among the functional entities involved in the design, development and construction of a project. According to the statistics from ITA Conference Seoul. April 25 2006. From 1994 to 2005, a total of 19 major tunnel losses failed due to fire, collapse earthquakes etc. and a total of 600million dollars lost due to these failures. These includes:Great Belt Link, Denmark, Munich Metro, Germany, Heathrow Express Link, GB, Metro Taipei, Taiwan, Metro Los Angeles, USA, Metro Taipei, Taiwan, Hull Yorkshire Tunnel, UK, TAV Bologna-Florence, Italy, Anatolia Motorway, Turkey, TAV Bologna-Florence, Italy, Metro Taegu Korea, Taiwan High Speed Railway, SOCATOP Paris, Shanghai Metro, PRC, Barcelona Metro, Spain, Singapore Metro, Singapore, Lausanne Metro, Switzerland, Lane Cove Tunnel, Sydney and Kaohsiung Metro, Taiwan.
Several researchers have used theories to analyze the risk involved in construction by formulating methods for analyzing and evaluating the risk involved in construction industry. This includes statistical and qualitative methods. Statistical Method:In this method there are two pre-requirements that has to be has to be fulfilled. These are the available data has to be sufficient in volume and the available data has to be based on conditions equal or very similar to that of the situation to be evaluated. Statistic evaluation of empirical data is possible in particular for technology risks. However, in tunneling like other construction, only segments have empirical data, in particular for the phase of realization, so that a sufficiently reliable data basis is not always available. Frequently, the planning and controlling systems that have been used in construction projects had not been analyzed and evaluated sufficiently with regards to effects of risks.Qualitative Method:according to Franke "Where objective data is not available, risks still have to be made quantifiable and estimable. One method is the qualitative estimation and weighing with which risks are subjectively evaluated for estimated probability of occurrence and damage amount. Therefore, expert discussions are used to evaluate project risks. Below are some of the method in which expert estimate and manage risks. Delphi method (Post mortem analysis):The Delphi method is a process of expert estimates over several steps and with a large number of experts. This is actually like a brain storm amongst experts, in other to identify the risk associated to construction and find solution to the risk identified. The Post-Mortem-Analysis, or PMA, can be successfully used as an instrument of risk identification and evaluation. The Post-Mortem-Analysis results in identification of process errors and malfunctions. The findings are contributed to a catalogue of risks for future projects. The Post-Mortem-Analysis also helps support the learning within the organization. Some other techniques which are frequently used include KJ method and the Root Cause Analysis. The KJ method was named after the Japanese ethnologist Jiro Kawakita helps in deeper understanding of the internal relations of a problem. Root Cause Analysis also called Ishikawa diagram or fishbone diagram is used for systematic determination of all causes of a problem (RISK).
Tunnel construction and planning present a challenge to all parties involved in the construction because tunneling is expensive underground construction where a variety of risks are associated with every phase of the project delivery process. Efficient tunnel construction planning requires the determination of the optimal sequence of tunnel excavation methods and primary support system based on available information. Evidence from some projects as shown that selecting tunnel excavation and support methods are not adequate, especially when considering the project completion cost and the project proposed cost. Therefore, estimating tunnel cost is problematic and remains a challenge. This, however is because the existing tunnel estimating approaches failed to address significant factors related to tunnel construction, namely, geological uncertainty, uncertainty in the productivity of tunneling processes, the dynamics of tunneling operations and a contractor's risk sensitivity.
Tunnels designing are different considerably from designing other conventional civil engineering structures such as buildings and bridges. In the design of conventional structures, the external loads applied to the structures are first determined, the structural geometry is the selected and the construction material prescribed with appropriate strength and deformation. In the tunnel design, however, the designer often deals with complex rock masses, the specific properties of which cannot be prescribed to meet the requirements The external loads resulting from the redistribution of the original stresses existing before excavation cannot be determined accurately. In addition, the configuration of geological structures and the availability of ground water, which are more significant for the tunnel stability than the external forces, are not considered in the design of conventional structure. Moreover, because most tunnels traverse a variety of geologic conditions, it is difficult to determine ground conditions along the tunnel alignment with certainty. Consequently, tunnel design always encounters challenges resulting from geologic anomalies and unexpected geologic features.
Tunnel design methodologies mostly used by rock tunnel designers are categorized into three approaches:Empirical methods, Analytical methods and Scaled physical methods and two principal methods used in rock tunneling are drill and blast methods, and tunneling machines. Typically, either of these two methods is applied for the entire excavation of a particular project. However, it is also possible to adopt several tunneling methods in the same project if it is considered to be more economical.
Risk assessment is the identification and analysis of risk. In rock tunneling there are several possible risks. This includes risk related to health, safety of workers, third parties, and delay in project completion, financial losses, and environmental impact. However these risks can be associated or traced to the geological conditions and construction technology used. It has been observed that most tunneling hazard result from improper selection of construction method and the geological conditions of the terrain. This ultimately causes financial losses to the company or contractors. Risk assessment in construction is carried out in every stage of the construction:starting from the tender stage to the actual construction of the project. The risk assessment being carried out in this early stage is used as part of the basis for decision making and contract negotiation
Generally, the risk assessment of a project can be defined as a unified procedure that includes identifying, analyzing, evaluating, and monitoring or mitigating of the associated risks. The level of risk for each threat is determined by finding the likelihood or the probability of occurrence and considering its consequences. The level of risk associated with the hazard is established mathematically as follows: Level of risk=PH*CH Ph=probability or likelihood of occurrence and Ch=consequences. The likelihood of a hazard occurring can be identified as Probable, Occasional and Remote.While the consequences can be identified as Catastrophic, Critical, Serious, Marginal and Negligible.
The tunnel construction industry's perception of risk associated with its activities and the extent to which the industry uses risk analysis and management techniques. It concludes that risk assessment is essential to construction activities in minimizing losses and enhancing profitability. Tunnel construction risk is generally perceived as events that influence project objectives of cost, time and quality. Risk assessment and management in construction depend mainly on intuition, judgment and experience. Formal risk assessment and management techniques are rarely used due to a lack of knowledge and to doubts on the suitability of these techniques for construction industry activities. The code of practice is the most recent development in risk management and is the most practical professional tools/method that ensures risk management principles are incorporated into the implementation of Tunnel and Underground Projects and that risks are managed to a reduced level "as low as reasonably practicable"
The development of the risk in tunnel construction has over the years increased as the method used in tunneling improved. It has been observed that the risk exposure in tunnel projects is extremely high due to various factors and loss experience in tunneling projects deteriorated to an unsustainable level in the last decade. Hence the need for effective risk assessment method.The review shows how the risks involved in tunnel construction has evolved and the progress that has been made to avoid increasing risk occurrence. Thus the need for continuous refining of risk assessment method, since the risk in construction industry cannot be totally removed but can be managed to a good proportion. Risk assessment that is successfully installed in a tunneling or construction project gives the chance of gaining a clearer understanding of the targets, duties, contents of services and the feasibility of the project and also provides fundamental information to support decision-making in the project as it concerns costs, deadlines and qualities.
In this research, rock tunneling risk scenarios will be classified into: Act of God risk scenarios, financial risk related scenarios, Design risk related scenarios and Construction risk related scenarios. A scenario is a synthetic description of an event or series of actions or events. In this case risk scenarios is said to be events that occur and causes damage or poses a threat to a project or event. The application of rock tunneling risk assessment methodology will be discussed. Various risk assessment method are created and used to check the identified risk associated with rock tunneling at every phase. The various methods discussed in this research, will show how they are used in different risk scenario or category and the risk assessment tools that they work with.
This study will be focusing on reviewing the different risk assessment methodology created to assess risks, stating the short comings of individual risk assessment method, comparing tunnel construction method using a risk assessment method and presenting the preferred. The methodology that will be adopted will be mainly the use of risk assessment software (palisade @RISK software) to run simulation on the cost estimation of a modeled project. Quantitative risk assessment method based on subjective judgments will also be adopted for the purpose of this research. From the risk assessment results in chapters 5 and 6, recommendations based on the results is made showing how Monte Carlo simulation gives a clear range of possible contingencies that may be needed in any particular project and the construction method that is most appropriate for rock tunneling (see).
隧道工程中潜在着许多风险。例如：凿隧道时遇到流动和含水的断裂带、在流动或块状地面上隧道壁不稳定、坚硬的或者腐蚀性的岩石断面以及收敛的岩石断面等等,这些都是风险存在的主要原因。近年来采用的施工方法是机械化掘进,这种方式最主要的问题是选取最合适的隧道掘进机以及在每种地质条件下的绩效预期与评估。以韩国青年洞隧道的建设为例,它就进行了详细的评估来确定哪种方法用于隧道施工是最好的。我们根据这项研究来探究导致中国工程安全管理薄弱的因素,得到的结论是：影响安全绩效的主要因素包括“高层领导者安全意思薄弱”、“缺乏训练”、“项目经理安全意识薄弱”“不愿意进行安全投资”以及“行动鲁莽”。工程风险被划分为三类：建设融资风险,建设工期风险以及施工设计风险,然后鉴于职能部门中合同方的不同,我们再将这些风险细分,因为这些合同方在设计、发展以及施工中发现风险与找到解决方案的过程中所起的作用不同。
从2006年4月25日召开的首尔ITA会议得来的数据来看,从1994年到2005年总共有19个主要的隧道工程因为火灾、地震坍塌造成了高达6亿美元的经济损失。这些工程包括：大贝尔特环线(丹麦),慕尼黑地铁(德国),西斯罗机场快线(国际),洛杉矶地铁(美国),台北地铁(台湾),赫尔——约克郡隧道(英国),博洛尼亚——佛罗伦萨(意大利),安纳托利亚高速公路(土耳其),韩国大邱地铁,台湾高速铁路,SOCATOP巴黎,上海地铁(中国),巴萨罗纳地铁(西班牙),新加坡地铁(新加坡),洛桑地铁(瑞士),Lane Cove隧道(悉尼),高雄地铁(台湾)
几位研究人员运用了一些理论来分析工程中所涉及的风险,运用函数的方法分析评价建筑行业中的风险。这包括统计和定性的方法。统计方法：在这个方法中,有两个预先的要求必须完成。这两个要求是指可用的数据量必须充分,并且这些可用的数据必须从与将要评估的项目的情况相同或者非常类似的条件中得来。经验数据的统计分析在研究技术风险中尤其可行。但是,隧道工程就像其他的工程一样,只有部分环节有经验数据,识别环节尤其缺乏经验数据,所以一个充足的、可靠地数据库并不是总是存在的。通常情况下,工程项目中的计划与控制系统并没有就风险的影响进行充分的分析与评估。定性的方法：根据弗兰卡的理论,即在客观的数据不可用,但我们仍然必须对风险进行定量分析与评估时,一种方法便是进行定性分析并衡量这些通过评估事故发生的可能性以及其造成的损失而主观判断出来的风险。因此,专家讨论被用来评估项目中的风险。以下是专家评估与管理风险的一些方法：德尔菲法、(Post mortem analysis)。德尔菲法是指大量的专家就一些环节进行专家评估。这其实就如在专家中实行头脑风暴法,来确定与施工相关的风险并找到与之对应的解决方法。终止后分析方法可以被充分的运用到风险的辨别和评估当中。(Post mortem analysis)分析的结果被运用于项目的错误与故障的鉴别当中。这些结果有助于为将来的项目进行风险归类。此外,终止后分析方法同样有助于组织内的学习。还有一些其他的经常使用的方法包括KJ法以及根本原因分析法。KJ法是以日本的人文学家喜田二郎的名字来命名的,他帮助我们更好的了解问题的内在联系。根本原因分析法也叫做石川图或鱼骨图,它被用来对一个问题的所有原因进行系统定位。
隧道施工和规划向所有的部门提出了挑战,因为隧道工程一个昂贵的、其实施的每个阶段都有许多风险存在的地下工程。高效的施工规划是指以现有的资料为基础,优化挖掘隧道的顺序并决定初期支护的方法。一些项目表明仅仅选择挖掘及支撑隧道的方法是不够的,尤其在我们要考虑到项目的完成成本与其预期成本时是不够得。因此,隧道成本估算仍旧存在困难。这是因为现有的评估方法不能将与隧道施工相关的效果显著的因素体现出来。例如,地质不确定性,隧道施工过程中生产效率的不稳定性,隧道运营动态和承包商对于风险的敏锐度。
隧道设计不同于其他传统市政工程(诸如房屋建筑与桥梁工程)的设计。在传统工程的设计上,应当首先确定外部荷载对结构的影响,选择几何结构和能满足承载力、变现要求的建筑材料。但对于隧道工程的设计,设计者往往先解决复杂交错的岩石群和那些不能满足需要的地块。因为挖掘而使原始压力重新分配的外部压力并不能正确的确定下来。另外,地理结构的外形和地下水的可用性,它们对于隧道稳定性的影响更加显著与外部的荷载,而这些因素在传统的项目中是不用考虑的。此外,大部分的隧道穿过的地址条件都不同,因此我们很难确定沿隧道走线的地质情况。所以,隧道设计总是遭遇到地质情况不同寻常所带来的挑战。
大多数由岩石隧道设计师使用的隧道设计方法可以分为三种：经验法,分析法和测量物理法。而用于岩石掘进的两种主要方法是岩石隧道爆炸法和掘进机法。通常情况下,只选择这两种方法中的一种应用于特定项目的整个开挖。但是,为了使其更加经济,也可以在同一项目中同时采用多种方法。
风险评估是风险的识别和分析。在岩石掘进过程中存在多种可能的风险。包括有关工人和第三方的健康安全风险,工期延迟,资金损失以及环境的影响。然而这些风险与相关地质条件或者所应用的施工技术有关。据观察,大部分隧道是由于施工方法以及地质条件的选择不当才导致灾害性的后果,这最终会导致本公司或承包商的经济损失。风险评估存在于项目建设的每一个阶段：从投资阶段到项目实际建设阶段。早期的风险评估是项目决策和合同谈判的基础。
一般而言,一个项目的风险评估被定义为一个统一的程序,包括识别,分析,评估,监测以及相关的风险缓解。每个威胁的风险水平,取决于风险发生的概率和所要考虑的后果。对于与灾害有关的风险水平可以建立如下数学公式：风险水平=PH*CH
(PH指风险发生的概率,CH指相关的后果)
灾害发生的可能性可以被认为是可能的,偶然的或微乎其微的。尽管后果可能是灾难性的,评判的,严重的,微小的和微不足道的。
有关隧道建造业风险的判断与它的活动以及需要应用风险分析和管理技术的扩展方面有关。由此得出的结论是,风险评估在减少损失和提高盈利能力方面是必不可少的。隧道风险常常被看做是影响项目的费用目标,工期目标和质量目标的重要因素,建设中的风险评估和风险管理主要依靠直觉,判断和经验。由于缺乏知识以及对一些技术应用于建造业活动的适用性的怀疑,正式的风险评估和管理技术很少使用。实践准则是风险管理的最新进展,它是保证风险管理原则能应用于隧道和地铁项目的最实用的专业方法,并且能设法保证风险达到最低的合理水平。
过去几年由于隧道施工技术的不断改进,在建设中出现的风险也发生了变化。据观察,过去十年间,由于各种因素和经验的缺乏,在隧道工程中的风险变得特别高,并且恶化到一种无法维持的水平。因此,必须采取有效的风险评估方法。评审显示了在隧道施工中涉及的风险是如何演变的以及在如何避免增加风险上所取得的进步。由于风险评估涉及费用、工期和质量,成功应用于隧道开挖或建设项目的风险评估,给出了更清晰的了解项目目标、职责服务内容和项目可行性的机会,并且也为项目决策提供了基本的信息。
在本研究中,岩石掘进风险情况将分为自然风险,金融相关风险情况,设计相关风险情况和施工相关风险情况。一种情况是对于一个事件或一连串的行动或事件的综合描述。在这种情况下,风险情况是指发生并造成损害或构成对一个项目威胁的事件,我也将对在隧道工程中应用风险评估方法进行讨论。各种各样的风险评估方法被创建并用于岩石掘进的每一个阶段。本研究将展示各种方法在不同风险类别中的应用以及他们所使用的风险评估的工具。
本项研究将着重于考察评估风险的不同评估方法,指出个别评估方法的缺点,比较在隧道施工中应用的风险评估方法,选出较优方法。本研究采用风险评估软件(Palisade公司开发的@RISK软件)来运行一个模拟仿真项目的成本估算,并且采用基于主观判断的定量风险评估方法进行分析。从评估的结果在第五和六章来看,结果显示了蒙特卡罗模拟是如何给出一系列在任何特定项目中可能存在的意外事件和对于岩石掘进来说最合适的建造方法。
The tunneling industry in the recent past has been characterized with several losses and accidents. Several factors have been attributed as the reason for these occurrences. These factors range from geological conditions to the improper design and inappropriate construction methods. Due to the complexity and huge cost required in tunnel construction, risk assessment has been considered very needful in every stage of tunneling from project bidding to planning down to the construction proper.
There are many potential sources of risk in rock tunneling. Problems such as encountering fault zones with running and water bearing gouge, tunnel walls instabilities in running or blocky grounds, hard and abrasive rock sections and convergent tunnel sections are principal causes in risk occurrence. In recent times mechanized tunneling is selected as construction method, the most important problem is often related to selection of the most appropriate TBM and its performance estimation and prediction in each geotechnical conditions. For instance in the construction of the young dong tunnel construction in Korea a detailed assessment was carried out to ascertain which method is best to be used in the construction of the tunnel. According to the survey to examine the elements of poor construction safety management in China and as a result, identified the main factors affecting safety performance including "poor safety awareness of top management", "lack of training", "poor safety awareness of project managers", "reluctance to input resources to safety" and "reckless operation". Also construction risks were classified into three groups, i.e. construction finance, construction time and construction design, and addressed these risks in detail in light of the different contractual relationships existing among the functional entities involved in the design, development and construction of a project. According to the statistics from ITA Conference Seoul. April 25 2006. From 1994 to 2005, a total of 19 major tunnel losses failed due to fire, collapse earthquakes etc. and a total of 600million dollars lost due to these failures. These includes:Great Belt Link, Denmark, Munich Metro, Germany, Heathrow Express Link, GB, Metro Taipei, Taiwan, Metro Los Angeles, USA, Metro Taipei, Taiwan, Hull Yorkshire Tunnel, UK, TAV Bologna-Florence, Italy, Anatolia Motorway, Turkey, TAV Bologna-Florence, Italy, Metro Taegu Korea, Taiwan High Speed Railway, SOCATOP Paris, Shanghai Metro, PRC, Barcelona Metro, Spain, Singapore Metro, Singapore, Lausanne Metro, Switzerland, Lane Cove Tunnel, Sydney and Kaohsiung Metro, Taiwan.
Several researchers have used theories to analyze the risk involved in construction by formulating methods for analyzing and evaluating the risk involved in construction industry. This includes statistical and qualitative methods. Statistical Method:In this method there are two pre-requirements that has to be has to be fulfilled. These are the available data has to be sufficient in volume and the available data has to be based on conditions equal or very similar to that of the situation to be evaluated. Statistic evaluation of empirical data is possible in particular for technology risks. However, in tunneling like other construction, only segments have empirical data, in particular for the phase of realization, so that a sufficiently reliable data basis is not always available. Frequently, the planning and controlling systems that have been used in construction projects had not been analyzed and evaluated sufficiently with regards to effects of risks.Qualitative Method:according to Franke "Where objective data is not available, risks still have to be made quantifiable and estimable. One method is the qualitative estimation and weighing with which risks are subjectively evaluated for estimated probability of occurrence and damage amount. Therefore, expert discussions are used to evaluate project risks. Below are some of the method in which expert estimate and manage risks. Delphi method (Post mortem analysis):The Delphi method is a process of expert estimates over several steps and with a large number of experts. This is actually like a brain storm amongst experts, in other to identify the risk associated to construction and find solution to the risk identified. The Post-Mortem-Analysis, or PMA, can be successfully used as an instrument of risk identification and evaluation. The Post-Mortem-Analysis results in identification of process errors and malfunctions. The findings are contributed to a catalogue of risks for future projects. The Post-Mortem-Analysis also helps support the learning within the organization. Some other techniques which are frequently used include KJ method and the Root Cause Analysis. The KJ method was named after the Japanese ethnologist Jiro Kawakita helps in deeper understanding of the internal relations of a problem. Root Cause Analysis also called Ishikawa diagram or fishbone diagram is used for systematic determination of all causes of a problem (RISK).
Tunnel construction and planning present a challenge to all parties involved in the construction because tunneling is expensive underground construction where a variety of risks are associated with every phase of the project delivery process. Efficient tunnel construction planning requires the determination of the optimal sequence of tunnel excavation methods and primary support system based on available information. Evidence from some projects as shown that selecting tunnel excavation and support methods are not adequate, especially when considering the project completion cost and the project proposed cost. Therefore, estimating tunnel cost is problematic and remains a challenge. This, however is because the existing tunnel estimating approaches failed to address significant factors related to tunnel construction, namely, geological uncertainty, uncertainty in the productivity of tunneling processes, the dynamics of tunneling operations and a contractor's risk sensitivity.
Tunnels designing are different considerably from designing other conventional civil engineering structures such as buildings and bridges. In the design of conventional structures, the external loads applied to the structures are first determined, the structural geometry is the selected and the construction material prescribed with appropriate strength and deformation. In the tunnel design, however, the designer often deals with complex rock masses, the specific properties of which cannot be prescribed to meet the requirements The external loads resulting from the redistribution of the original stresses existing before excavation cannot be determined accurately. In addition, the configuration of geological structures and the availability of ground water, which are more significant for the tunnel stability than the external forces, are not considered in the design of conventional structure. Moreover, because most tunnels traverse a variety of geologic conditions, it is difficult to determine ground conditions along the tunnel alignment with certainty. Consequently, tunnel design always encounters challenges resulting from geologic anomalies and unexpected geologic features.
Tunnel design methodologies mostly used by rock tunnel designers are categorized into three approaches:Empirical methods, Analytical methods and Scaled physical methods and two principal methods used in rock tunneling are drill and blast methods, and tunneling machines. Typically, either of these two methods is applied for the entire excavation of a particular project. However, it is also possible to adopt several tunneling methods in the same project if it is considered to be more economical.
Risk assessment is the identification and analysis of risk. In rock tunneling there are several possible risks. This includes risk related to health, safety of workers, third parties, and delay in project completion, financial losses, and environmental impact. However these risks can be associated or traced to the geological conditions and construction technology used. It has been observed that most tunneling hazard result from improper selection of construction method and the geological conditions of the terrain. This ultimately causes financial losses to the company or contractors. Risk assessment in construction is carried out in every stage of the construction:starting from the tender stage to the actual construction of the project. The risk assessment being carried out in this early stage is used as part of the basis for decision making and contract negotiation
Generally, the risk assessment of a project can be defined as a unified procedure that includes identifying, analyzing, evaluating, and monitoring or mitigating of the associated risks. The level of risk for each threat is determined by finding the likelihood or the probability of occurrence and considering its consequences. The level of risk associated with the hazard is established mathematically as follows: Level of risk=PH*CH Ph=probability or likelihood of occurrence and Ch=consequences. The likelihood of a hazard occurring can be identified as Probable, Occasional and Remote.While the consequences can be identified as Catastrophic, Critical, Serious, Marginal and Negligible.
The tunnel construction industry's perception of risk associated with its activities and the extent to which the industry uses risk analysis and management techniques. It concludes that risk assessment is essential to construction activities in minimizing losses and enhancing profitability. Tunnel construction risk is generally perceived as events that influence project objectives of cost, time and quality. Risk assessment and management in construction depend mainly on intuition, judgment and experience. Formal risk assessment and management techniques are rarely used due to a lack of knowledge and to doubts on the suitability of these techniques for construction industry activities. The code of practice is the most recent development in risk management and is the most practical professional tools/method that ensures risk management principles are incorporated into the implementation of Tunnel and Underground Projects and that risks are managed to a reduced level "as low as reasonably practicable"
The development of the risk in tunnel construction has over the years increased as the method used in tunneling improved. It has been observed that the risk exposure in tunnel projects is extremely high due to various factors and loss experience in tunneling projects deteriorated to an unsustainable level in the last decade. Hence the need for effective risk assessment method.The review shows how the risks involved in tunnel construction has evolved and the progress that has been made to avoid increasing risk occurrence. Thus the need for continuous refining of risk assessment method, since the risk in construction industry cannot be totally removed but can be managed to a good proportion. Risk assessment that is successfully installed in a tunneling or construction project gives the chance of gaining a clearer understanding of the targets, duties, contents of services and the feasibility of the project and also provides fundamental information to support decision-making in the project as it concerns costs, deadlines and qualities.
In this research, rock tunneling risk scenarios will be classified into: Act of God risk scenarios, financial risk related scenarios, Design risk related scenarios and Construction risk related scenarios. A scenario is a synthetic description of an event or series of actions or events. In this case risk scenarios is said to be events that occur and causes damage or poses a threat to a project or event. The application of rock tunneling risk assessment methodology will be discussed. Various risk assessment method are created and used to check the identified risk associated with rock tunneling at every phase. The various methods discussed in this research, will show how they are used in different risk scenario or category and the risk assessment tools that they work with.
This study will be focusing on reviewing the different risk assessment methodology created to assess risks, stating the short comings of individual risk assessment method, comparing tunnel construction method using a risk assessment method and presenting the preferred. The methodology that will be adopted will be mainly the use of risk assessment software (palisade @RISK software) to run simulation on the cost estimation of a modeled project. Quantitative risk assessment method based on subjective judgments will also be adopted for the purpose of this research. From the risk assessment results in chapters 5 and 6, recommendations based on the results is made showing how Monte Carlo simulation gives a clear range of possible contingencies that may be needed in any particular project and the construction method that is most appropriate for rock tunneling (see).
引文
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