某运营高铁隧道上部大型溶洞演化致灾与处置方案研究

Research on disaster caused by evolution of large karst caves in the upper part of an operating high-speed railway tunnel and its disposal scheme

针对某运营高铁隧道2019年6月因强降雨后在施工期揭示上部有大型溶洞的段落发生灾害的工程实际,介绍施工期揭示溶洞及变更对策、运营期灾害及应急措施的主要情况,通过对勘察、设计和施工各阶段的检视,分析溶洞演化致灾的机制,并在指出两次泄水洞整治方案存在不足的基础上提出"护拱+强堵+预留疏排+固结和轻质密实回填"相结合的咨询方案,再与泄水洞方案在可行性、工作条件、工期、投资、风险、环境影响及效果预测等方面进行比对,并采用FLAC3D建立三维模型对其安全性进行检算。研究成果表明:在季节性强降雨时,雨水经地表与溶洞间的溶隙、溶槽、管道形成径流,流入因修建隧道使充填型转型为充水和过水型的溶洞,溶洞与隧道间介质在季节性溶洞充水和过水甚至短期承压的作用下形成径流场水力通道,携带泥沙的溶洞充水和过水进入隧道内形成灾害;以"护拱+强堵+预留疏排+固结和轻质密实回填"为主的咨询方案在环境保护、投资控制、工期、施工风险等方面比泄水洞方案具有显著优势;以施工期地下水观测及其水量估算作为处置大型溶洞的依据,忽视工程活动对地下水力场的诱导性演化预判,必将导致在隧道建成后一定的时段内演化致灾,工程中未维持和(或)构建具有维护功能的地下水人工排泄通道,使灾害仅运营一年半就出现;并建议新建隧道时对富水段或潜在富水段实施单元区隔防排水的特殊措施。

This paper was based on the engineering practice of a large karst cave(this cave was revealed during the construction period)in the upper part of a high-speed railway tunnel in June 2019.The main situation of revealing karst cave and its change countermeasures,disasters and emergency measures during the operation period was introduced,and the mechanism of karst cave evolution disaster was analyzed through the inspection of each stage during investigation,design and construction.A consultation scheme combining“arch protection+strong blocking+reserved drainage+consolidation and lightweight compact backfilling”was put forward,which was on the basis of pointing out the shortcomings of the two drainage tunnel renovation schemes.The feasibility,working conditions,construction period,investment,risks,environmental impact and effect prediction was compared with the drainage tunnel scheme.A three-dimensional mode was established by FLAC3D to check the safety of tunnel.The research results were as follows:The karst cave with filling type was changed into water-filled and water-flowing type due to the construction tunnel.And water flowed into the karst cave by the type of runoff,which was formed by the dissolution gap,dissolution tank,pipeline between the surface and the karst cave during seasonal heavy rainfall.The disaster was formed by sediment entering the tunnel with the karst cave water-filled and water-flowing;the runoff field hydraulic channel was formed by the medium between the karst cave and the tunnel under the action of seasonal karst cave water-filled and water-flowing or even short-term pressure.The consultation scheme of“arch protection+strong blocking+reserved drainage+consolidation and lightweight compact backfilling”had significant advantages over the drainage tunnel scheme in terms of environmental protection,investment control,construction period and construction risks.It would necessarily lead to the evolution of disasters within a certain period of time after the completion of tunnel,by taking groundwater observation and water quantity estimation during the construction period as the basis for disposal of large karst caves and ignoring the induced evolution prediction of groundwater force field caused by engineering activities.So the disaster was appeared only after one and a half years of operation because of failure to maintain and construct the artificial drainage channel of groundwater with maintenance function.In addition,it was suggested that special measures of unit separation water prevention and drainage should be implemented for water-rich sections or potential water-rich sections when new tunnels were built.