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ZnO nanowires on the a-, c-and m-plane oriented 4H-SiC substrates were grown by using a high temperature tube furnace. Ti/Au electrodes were deposited on ZnO nanowires and a-, c-and m-plane 4H-SiC substrates, respectively. The shape and density of the ZnO nanowires were investigated by field emission scanning electron microscope. It was found that the growth direction of nanowires depends strongly on growth parameters such as growth temperature and pressure. In this work, The sensitivity of nanowires formed a-, c-and m-plane oriented 4H-SiC gas sensor was measured at 300℃ with CO gas concentration of 80%. The nanowires grown on a-plane oriented 4H-SiC show improved sensing performance than those on c-and m-plane oriented 4H-SiC due to the increased density of nanowire on a-plane 4H-SiC.Keywords: 4H-SiC, CO gas sensor, Nanowire, Substrate orientation

In general, risk management consists of a series of processes or steps including risk identification, risk analysis, risk evaluation, risk mitigation measures, and risk re-evaluation. In this paper, potential risk factors that occur in shield TBM tunnels were investigated based on many previous case studies and questionaries to tunnel experts. The risk factors were classified as geological, design or construction management features. Fault Tree was set up by dividing all feasible risks into four groups that associated with: cutter; machine confinement; mucking (driving) and segments. From the Fault Tree Analysis (FTA), 12 risk items were identified and the probability of failure of each chosen risk item was obtained.

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In this paper, a risk analysis methodology applicable to shield TBM tunnels was studied. Fault Tree Analysis (FTA) was utilized to identify all risk items and to calculate the probability of failure of each item and Analytic Hierarchy Process (AHP) was used to obtain the impact of each risk item. Finally, a risk level of each risk item can be assessed. Developed methodology is applied to a Seoul subway site in which EPB shield tunnel method was utilized and it was found that risk analysis results matched reasonably well with field data. 주요어: 쉴드 TBM 터널, 리스크 분석, 리스크 요인, fault tree analysis, analytic hierarchy process