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Taiwan is situated on the junction belt of Philippine Sea plate and Eurasian plate, which subjected to collision and compression activities. The geologic structures are complex and presenting great variations. Therefore, failures occurred frequently during tunnel constructions. Sometimes the magnitude and the extent of the failures were so large that even the most experienced engineers could not resolve the problem. When drilling tunnels through the mountain, it would involve certain engineering features such as advanced techniques, great risks, obscure uncertainties, time efficiencies, high costs, and continuous and cyclic work schedules. During the tunnel construction, failures such as collapsing, rock fall, caving- in, squeezing, water inrush, geothermal, hot spring, rock burst and toxic gases may be encountered. Among these, the most difficult situation is to fight with the massive high-pressured catastrophic inrush of groundwater. Numerous case histories regarding water inrush problems have been collected and studied herein. The special geologic features that cause the water inrush and the phenomenon of failures induced by the water inrush can be summarized as following: 1. Groundwater intruding into the tunnel from all over the circumferences, for the cases that ample groundwater existing in the highly permeable surrounding rocks. 2. Groundwater with extremely high pressure that penetrates through the discontinuities of rocks or through the permeable strata. 3. Tunnelling encounters underground water flow such as the soluble cavities, openings of discontinuities, or crushed zones. 4. Tunnelling underpasses ocean, lake, river, etc. Some important items in the hydrogeological investigation program, for those grounds with water inrush potential, have been analyzed and classified. This is to further understand the causes of tunnel water inrush and the travelling passages of water to facilitate the prediction of the quantity of water inrush and as the fundamental for the remedial approaches planning. These investigation items include: direction of water flow, boundary of impermeable layer which surrounding the tunnel, fault and crushed zone, acquifer in soluble rock (Karst formation), geothermal and ground temperature. The treatment methodologies for inrush of water problems can be classified according to the theoretical fundamentals, geologic characteristics and the results of applied methods, as addressed in the collected case histories. They can be split into two major categories, namely water diverting and water stopping methods. In the recent years, in view of the complexity of the ground conditions, the local constructors have used, at the same time, both of the methods to deal with the water inrush problems. This methodology is implemented by applying low pressure grouting for the area near the tunnel excavation face meanwhile diverting the water behind the grouting area. A practical case, New Yong-Chun tunnel, is studied herein. The results of geological investigation during the planning and design stage, considerations in response to the water inrush problems, supplemental construction methods, results of hydrogeological and geological investigations during tunnelling have been carefully reviewed. A detailed description of encountering the high-pressured catastrophic inrush of water during tunnel construction is also included. In addition, cautious assessment is carried out regarding to the adopted remedial treatments after the massive water inrush occurred, which including the activities of supplemental geological investigations from the ground surface, long-run horizontal drilling, modification in tunnel alignment, and supplemental methodologies. It has indicated that the large dimensional water diversion device constructed at the west side bypass has effectively released the water and its pressure. On the other hand, a grouting work is also performed to hinder the water inflow, by using hot bitumen as the grouting material. Grouting incorporation of the hot bitumen has shown that the hardening processes are different from those of the traditional materials. The temperature rather than the time mainly control the hardening of the bitumen. During the grouting, the equipment, material supply and other necessary accessories would become a unique operation system. Since the system consists of many elements, whenever any of them is not functioning normally it will shut down the whole system. In the studied case, there had been occasions the grouting work could not proceed smoothly only due to certain minor problems. The application of hot bitumen grouting in tunnelling has never been used in Taiwan before. Therefore it is lacking of related experiences and test data. The information collected in this study, including grouting processes, effectiveness of grouting and the test results, may serve as a good reference for future researches on the establishment of the mechanical behaviors, transferring of grouting techniques and issues of localization for the hot bitumen grouting. The intention of this study is to summarize the related case histories of tunnelling subjected to water inrush problems and to fully search into a practical case regarding the subjects of investigation, assessment, and the action strategies, It is expected that that study would provide useful references
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