Abstract Underwater shield tunnel construction in karst ground is a huge challenge for engineers and technicians since such engineering case is rarely seen and there are no reported experiences in the literature. The shield tunnel of Changsha metro line 3 had to pass through underwater karst regions in a water conservation district of Xiangjiang River. Therefore, guaranteeing the construction safety and protecting the river water quality during the shield tunneling process are the main difficulties need to be solved. A new controllable grouting method and two corresponding grouting materials were proposed in this paper to pre-reinforce the underwater karst region before shield tunnel passing. The karst caves in the vicinity of the tunnel body were pre-grouted by a so called vertical layered controllable grouting, which can ensured the grouted are to be easy cutting by the shield machine but possess sufficient strength to keep the stability of the tunnel. This specific field pre-grouting scheme mainly includes a waterborne construction platform and a series of anti-pollution measures. The effectiveness of field application of the proposed scheme were evaluated by a series laboratory tests taking the samples from the grouted area. The result indicates that the grouting activities not only meet the engineering requirements but they are also environmental and ecological friendly. The presented study could provide a detailed case experience and reference technology for tunnelling in underwater karst area.

中文翻译：

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长沙穿湘江盾构隧道水下岩溶区预灌浆加固

摘要 岩溶地层水下盾构隧道施工对工程技术人员来说是一个巨大的挑战，因为这样的工程案例很少见，文献中也没有经验报道。长沙地铁3号线盾构隧道穿越湘江水源涵养区水下岩溶区。因此，在盾构施工过程中，保障施工安全和保护河道水质是需要解决的主要难点。提出了一种新的可控注浆方法和两种相应的注浆材料，在盾构隧道通过前对水下岩溶区域进行预加固。洞身附近溶洞采用所谓垂直分层可控灌浆进行预灌浆，既能保证灌浆容易被盾构机切割，又具有足够的强度来保持隧道的稳定性。这个具体的现场预灌浆方案主要包括一个水上施工平台和一系列的防污染措施。通过从灌浆区取样的一系列实验室测试，评估了所提出方案的现场应用的有效性。结果表明，灌浆活动不仅满足工程要求，而且对环境和生态友好。该研究可为水下岩溶地区隧道掘进提供详细的案例经验和参考技术。这个具体的现场预灌浆方案主要包括一个水上施工平台和一系列的防污染措施。通过从灌浆区取样的一系列实验室测试，评估了所提出方案的现场应用的有效性。结果表明，注浆作业不仅满足工程要求，而且对环境和生态友好。该研究可为水下岩溶地区隧道掘进提供详细的案例经验和参考技术。这个具体的现场预灌浆方案主要包括一个水上施工平台和一系列的防污染措施。通过从灌浆区取样的一系列实验室测试，评估了所提出方案的现场应用的有效性。结果表明，灌浆活动不仅满足工程要求，而且对环境和生态友好。该研究可为水下岩溶地区隧道掘进提供详细的案例经验和参考技术。结果表明，灌浆活动不仅满足工程要求，而且对环境和生态友好。该研究可为水下岩溶地区隧道掘进提供详细的案例经验和参考技术。结果表明，灌浆活动不仅满足工程要求，而且对环境和生态友好。该研究可为水下岩溶地区隧道掘进提供详细的案例经验和参考技术。