Risk Management

Multiphase Risk-Management Method and its Application  in Su’ai Tunnel

Background
       When analyzing the research trend of risk-management in underground engineering for both domestic and overseas, conclusions can be drawn that for most risk-management of underground engineering projects, researchers usually only focus on the procedure before construction. This kind of risk-management lacks continuity as well as the dynamic management of underground engineering projects, and belongs to the static risk-management paradigm. The shortcoming of static risk-management lies in its artificially dividing the project progress into two independent states: the present condition and the future condition. This kind of risk-management analyzes the risk according to present condition while the management job is according to the future. However, underground engineering projects has uncontrolled factors which changes the previous risk analyzes, which means that the effect cannot meet the demand.
Significance
       The geological conditions of the Su’ai Tunnel are rarely seen domestically. The tunnel faces extremely high-risk engineering because it’s located in an area where the earthquake intensity is degree 8. The Su’ai Tunnel project is the leading Shantou project for the south coast development plan. The tunnel attracts high social awareness and will have large industry impacts, thus has a high public opinion risk. Based on the reasons listed above, it is necessary to apply an advanced risk-management method on the Su’ai Tunnel Project.
Contents
1) Build a sophisticated risk evaluation system.
       For a tunnel faced with such high risk, it is imperative to build a sophisticated risk evaluation system. This research prepares and introduces the dynamic risk- management paradigm and the diversity of risk will be exhibited. A risk evaluation software will be developed to assess the comprehensive risk of each construction procedure, so that it meets the demand of dynamic risk management.
2) Make a sophisticated risk response plan.
       Put forward detailed measures for expected risk and give advice to cope with accidental risk emerging for each construction procedure.
3) Set up risk database.
       At the end of this project, submit the risk-management report and set up the Su’ai tunnel risk database based on the risk exposed during the construction and its corresponding measures for later use.

 

 Fig. 1 Process of dynamic risk-management.


Descriptions of the flowchart:
1.Risk assessment of the overall plan.
       Based on the construction methods and site conditions, determine risks that may occur in the following procedure, do the initial risk assessment job, and raise corresponding solutions.
2.Mitigation measures.
       Generally the best the mitigation plan consists of several different plans leading to the reduction of risk with the minimum cost.
3.Expected risk.
       Risks analyzed in the risk assessment procedure. For these kind of risks, follow the mitigation measures carried out before to mitigate risk.
4.Accidental risk.
       Risks not analyzed in the risk assessment procedure. For these new risks emerged, the risk assessment needs to be repeated. If the risks can be classified as acceptable risk, then go on the project, but if the risks are unacceptable, mitigation measures must be taken until it meets the demand of risk management.
Achievement and Conclusion
1)Raise theoretical models of multiphase risk evaluation.
       The initial risk of tunneling engineering is usually expressed as a combination of the occurrence probability (P1) and the potential loss (C1), and can be formulated as. It can be expressed in two-dimensional graphics with the horizontal ordinate being P1 while the vertical axis being C1, which can be seen in Fig.2.
The secondary risk can be expressed as a combination of the risk probability (P2), the potential loss (C2), and the mitigation cost (T1), in the form of . After the taken of mitigation measures arising from the initial risk, the occurrence probability or the potential loss may decrease. The ternary properties of secondary risk can be seen in Fig.2.

 


Fig. 2 Initial risk and secondary risk

 

       According to the risk acceptable rules, based on the results of the risk evaluation, risks can be divided into three types: acceptable risk, acceptable risk after mitigation, and unacceptable risk (Fig. 3).

 

Fig. 3 Three types of risk

 

       If the initial risk is located in the lower left corner of the bottom area in Fig. 4, it is acceptable. This kind of risk is allowed without any further mitigation. However, monitoring during construction is still necessary even for projects deemed to have an acceptable risk profile, and appropriate emergency plans should still be prepared.

 

 

Fig. 4 Acceptable risk

 

       If the initial risk is located in the upper right corner of the top area in Fig. 5, it is unacceptable, and appropriate mitigation measures must be implemented. If the secondary risk after mitigation falls into the green area, as shown in Fig. 5, it belongs to the acceptable risk after suitable mitigation category. If, however, the secondary risk after mitigation is still located in the red area, as shown in Fig. 6, then it belongs to the unacceptable risk category, and the project cannot be implemented in its current state.

 

Fig. 5 Acceptable risk after mitigation

 

Fig. 6 Unacceptable risk

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