成贵高铁玉京山隧道巨型溶洞顶板防护技术研究

Roof Protection Technology for Giant Karst Cave in Yujingshan Tunnel of Chengdu-Guiyang High-Speed Railway

成贵高铁玉京山隧道穿越巨型溶洞,溶洞顶板处有大直径不稳定楔形体,为防止施工过程中隧道顶部出现掉块和坍塌,提出采用涨壳式中空注浆锚杆与低预应力全黏结型锚索联合加固溶洞顶板的治理措施。采用有限元软件分别建立顶板无支护、仅设置锚杆支护及锚杆和锚索联合支护3种工况下围岩的三维数值模型,同时考虑支护滞后时顶板围岩的加固效果,通过数值模拟结果对比分析不同工况下锚杆、锚索轴力的变化规律及围岩位移、塑性区的分布规律,并提出一种有效的顶板防护措施。结果表明:1)锚杆和锚索及时支护可以有效控制顶板不稳定围岩的位移、塑性区发展,达到较好的加固效果;2)在仅设置锚杆的基础上及时施加锚索结构可以显著降低锚杆的轴力,避免锚杆因轴力太大而破坏;3)采用涨壳式中空注浆锚杆与低预应力全黏结型锚索结构对玉京山隧道溶洞顶板进行加固可以保障隧道施工安全。

The Yujingshan tunnel of Chengdu-Guiyang high-speed railway passes through a giant karst cave.There is a large-diameter unstable wedge-shaped body at the roof of the karst cave.To prevent the tunnel roof from falling off and collapsing under this working condition,a joint reinforcement of the roof with an expanded shell hollow grouting anchor rod and a low prestressed fully bonded anchor cable is proposed.Furthermore,three-dimensional numerical models of the surrounding rock with no roof support,only bolt support,and combined support with bolts and anchor cables are established using the finite element software.Meanwhile,the reinforcement effect of the roof surrounding rock when the support is lagging is considered.A comparative analysis is conducted on the variation rules of the anchor rod,the axial force of the anchor cable,the displacement of the surrounding rock and the plastic zone.Finally,an effective roof protection measure is found.The results show the following:(1)The timely bolt and cable support can effectively control the displacement of unstable surrounding rock and the development of plastic zone,achieving good reinforcement effect.(2)The axial force of anchor rod can be significantly reduced by applying anchor cable structure in time,so as to avoid the failure of anchor rod due to over-large axial force.(3)The application of expanded shell hollow grouting anchor and low prestressed fully bonded anchor cable structure can guarantee the safety of the Yujingshan tunnel.