捷运潜盾隧道皆位于人口密集之都会区，潜盾机的发进与到达常为潜盾隧道挖掘过程中风险较大的时间点，本研究拟以潜盾机到达弃壳作业为例，探讨其面临之风险，包括点井降水造成地盘地下水位变化和邻近台电345kV高压电塔不均匀沉陷，以及站体连续壁因开挖所引致侧向变位使JSG地盘改良区产生缝隙水路，造成潜盾机开舱前渗水的风险。再者，依据工址抽降水期间竖管式水压计、水位观测井和地表、建物沉陷点监测数据分析抽降水引致地表沉陷影响范围，用以回馈将来遭遇类似工况的设计参考依据。
　　潜盾机到达之安全弃壳作业包括以超级点井(SWP)工法尝试降低地下水位，并于松三层(EL. 92.42m)和松五层(EL.72.42m)埋设竖管式水压计了解降水期间地下水位变化，同时监测邻近建物如台电高压电塔的倾斜及沉陷；其次，在潜盾机到达处先行进行JSG地盘改良，再以试水试验检核地盘止水性，潜盾机到达后即进行机壳背填灌浆、土压舱分阶排土及漏水确认。然后，潜盾机历经二次拆解，完成到达弃壳作业，最后进行镜面破除及隧道贯通。

The maximum risk for shield tunneling construction is shield machine approached ventilation shaft and left that. The variation of ground water table and nonuniform settlement of Taipower 345 kV pylon by super well point (SWP) dewatering will be discussed. And further, the lateral displacement of diaphragm wall might cause seepage at mirrorface during the excavation stage, therefore that will be also discussed.
The decomposition of shield machine include several works, that is dewatering by SWP, and install standpipe piezometer to measure the variation of ground water table at 3rd SongShan layer(EL.92.42m) and 5th SongShan layer(EL. 72.42m), respectively. In addition, nonuniform settlement of nearest building such as Taipower 345kV pylon is monitored. The JSG grouting was conducted for ground soils outside the diaphragm wall several weeks before shield machine approached and then the leakage test for JSG grouting soilcrete is conducted. The backfill grouting is executed immediately when shield machine approached. Finally, there are two stages to decompose shield machine, that remove cutter face, cutter motor and screw conveyor, respectively. Therefore, the mirrorface can be broke safely and through the shield tunnel.