A Study of Reconstruction for Ground Settlement – The LUO09 Shield Tunnel for the Kaohsiung MRT System CO2 Section
捷運 ； 復建工程 ； 填充灌漿 ； 滲水 ； 冷凍工法 ； MRT ； Reconstruction ； Grouting ； Leakage ； Ground Freezing Method
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高雄捷運潛盾隧道進行聯絡通道內集水井最後一階開挖時，開挖側面局部突然發生湧砂水現象，造成聯絡通道、潛盾隧道及聯絡通道上方之車行地下道結構損壞，導致地表與路面塌陷，事故地點位處交通要道，因此如何進行復建工程成為各界矚目焦點。 復建工程應用之工法，初期以七種方案進行評估，經重複檢討後選擇對既有設施影響最小之「開挖內撐及局部冷凍工法」作為主要應用工法；開挖區以厚度1.5m、深度 60m之連續壁作為擋土水措施，開挖深度30.2m，開挖完成後於現地組裝預鑄環片及構築聯絡通道與集水井，而回填作業則以CLSM作為主要回填材料；除開挖區以外之受損隧道，採冷凍工法構築受損環片更新作業之安全空間，配合冷凍運轉階段進行隧道洞口反力座及重力牆之拆除，接續進入隧道清除淤積之土砂後，開挖凍土進行受損環片之更新作業，冷凍區共4處，冷凍深度約GL-19.4m~-30.5m，總凍土體積約5700m3。 復建工程之前置作業先以鑽孔調查隧道內土砂狀況並進行填充灌漿，以利連續壁及冷凍工程可順利進行，而開挖區開挖期間曾出現滲水現象，經採止水灌漿並進行抽水試驗驗證成效後，讓開挖作業得以繼續執行，因高雄地區並無冷凍工法案例，故施工前需進行凍脹及融沉之預測與檢討，為避免回填產生之沉陷對鋪軌作業造成負面影響，應用控制回填土單位重與地下水回升時機之施工管控，及適當的沉陷量評估方式，讓鋪軌作業得以依預定時程順利完成。
During the last stage of excavation of cross passage between two running tunnels in Kaohsiung metro project, water and soil spurted out from the side of the pit suddenly and then caused damage of cross passage, running tunnel and structure of underpass above the metro tunnels. A large sinkhole was also seen after the accident. The accident occurred located on the main road so attentions were paid for reconstruction herein. Seven different methods were considered and evaluated for reconstruction and the method of “excavation with internal bracing and partial ground freezing” was selected at the end. In excavated area, the pit was retained by 1.5m thick, 60m deep diaphragm wall and the maximum excavation depth was 30.2m. After completion of excavation, the precast tunnel segments were erected in situ and then cross passage and sump were constructed. CLSM was used for the material for backfill. Except the excavated area, ground freezing method was used for the rest first in order to remain a safe space for construction. After ground was frozen, the reaction walls were removed and dust inside the tunnel was cleaned. The damaged segments were thus replaced. The ground was frozen in 4 different locations and it is from 19.4 to 30.5m below surface level and total volume of frozen soils is approximately 5700m3. In order to smoothly take the construction of diaphragm wall and ground freezing, conditions inside the tunnel were investigated using borehole exploration and necessary grouting was undertaken in advance. Spurting of water was observed during the excavation and grouting and pumping test were carried out in order to ensure the safety of the excavation. Since no similar experience can be referred in Kaohsiung previously for ground freezing, it has to evaluate the effect from swelling and sinking caused by ground freezing before the construction since negative influences on track from these factors should be prevented. By the use of successful control of construction of unit weight of backfill material and recovery of groundwater level as well as adequate settlement evaluation model, the paving of track thus could be completed on time.
工程學 > 土木與建築工程
工程學 > 市政與環境工程