巨型溶洞回填处置与超厚回填体沉降机制研究

黔张常铁路高山隧道施工时揭露一处巨型溶洞,溶洞体量巨大、发育复杂、围岩稳定性差且落石风险高,隧道穿越距离长(影响区总长145 m),悬空高度大(隧道底板下净空30～55 m),施工处置难度高;通过综合比选,采用了"洞砟回填+上部注浆"的综合处置方案。针对超厚回填体可能产生的沉降问题,采用现场监测、数值模拟和理论分析的方法,对回填体静载作用下和动载作用下的沉降规律进行综合研究。施工期表层沉降和分层沉降监测表明,超厚回填体表层沉降主要受回填洞砟自身重力及上部新增结构荷载的影响,沉降收敛速度快,沉降主要来源于下部未注浆回填体和溶洞底部堆积体的表层部分。通过有限元软件建立三维数值仿真模型,模拟列车动载作用对超厚回填体的影响,分析表明有砟轨道和3 m厚钢筋混凝土路基板大幅降低了列车动应力向下部回填体的传递,再经过回填体上部注浆层阻断,回填体未注浆层基本不受列车动载影响,即列车动荷载不会造成回填体新增沉降量。工程实践表明黔,张常铁路高山隧道巨型溶洞回填处置可靠,工后沉降可控,满足设计要求,可为其他类似工程提供参考。

Study on backfill treatment of huge karst caves and settlement mechanism of super thick backfill

Gaoshan tunnel of Qianjiang-Zhangjiajie-Changde railway goes through a huge karst cave with a long crossing distance(the affected area of the cave up to 145 m)and a large suspended height(the clearance under the tunnel floor up to 30-55 m),and the cave has unfavorable conditions including large volume,complex structure,poor stability and high risk of falling rock,which makes the construction and treatment of the tunnel to be very difficult.In order to overcome the above-mentioned issues,a treatment scheme of"backfill with tunnel ballast+upper grouting"was proposed through comprehensive comparisons,and the settlement pattern of the backfill under static and dynamic loads was comprehensively studied by using field monitoring,numerical simulation and theoretical analysis.The monitoring results during the construction period show that the surface settlement of the super thick backfill-body is mainly affected by the gravity and the load of the upper structure and the convergence rate of the settlement is fast.The settlement is mainly resulted from the lower un-grouted backfill and the surface part of the deposit at the bottom of the karst cave.A 3D numerical simulation model was established based on finite element method to simulate the influence of the dynamical load of trains on the super thick backfill-body.The simulation results show that,due to that the transfer of the dynamical stress of the train to the super thick backfill is largely reduced because of the exist of the ballast track and the 3 m-thick reinforced concrete subgrade and further blocked by the upper grouting layer of the backfill body,the un-grouted layer of the backfill body is nearly not affected by the dynamic load,that is,the dynamic load of the train will not cause an additional settlement value of the backfill.The engineering practice shows that the backfill treatment of the huge karst cave in Gaoshan tunnel of Qianjiang-Zhangjiajie-Changde railway is reliable,that the settlement after the construction is under control and meets the design requirements.The proposed technology can be adopted as a reference for other similar kind of projects.