Application Of Rock Tunneling Risk Assessment Methodology

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 negotiationGenerally, 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).