百丈隧道穿越流塑状富水破碎带施工措施及其安全性评价

百丈隧道左洞ZK152+433~ZK152+463段穿越流塑状富水破碎带施工时反复出现变形侵限、塌方等情况,给工程施工带来前所未有的挑战。文章详细阐述了施工过程中采取的各种处治措施,总结了不同处治方案和效果,并采用数值分析方法对隧道结构安全性进行了分析。结果表明:(1)对于流塑状富水破碎带,加密超前支护是防止开挖时围岩出现较大变形或者坍塌的最有效措施。百丈隧道流塑状富水破碎带最终采用了每榀钢架(钢架间距50 cm)都打设一环3.5 m长?51自进式锚杆的超前支护方式,即每个断面都有7层超前支护,最终有效控制了开挖后围岩变形,避免衬砌侵限与塌方;(2)对于流塑状富水破碎带,加固围岩尤其是边墙与基底处围岩非常重要,可有效减少开挖过程中衬砌的整体式下沉。采用抛石挤淤+注浆的方式进行边墙与基底围岩加固,其效果比采用单纯注浆方式好得多;(3)对于外部荷载较明确的隧道,采用计算分析结合工程经验的方式确定衬砌支护参数,既能保证隧道结构安全,又使其经济合理;(4)在双车道隧道施工中,采用三台阶法施工,应尽量缩短台阶长度,使初期支护及时封闭成环,从而可以较好地控制围岩变形。

Engineering Measures and Safety Evaluation of Baizhang Tunnel Passing through Flow Plastic Water-rich Fracture Zone

Collapse and clearance invasion events occurred repeatedly during the construction at the section of ZK152+433-ZK152+463 of left tube of Baizhang tunnel passing through a flow-plastic fracture zone with abundant water,which brought unprecedented challenges to the engineers.The various measures adopted in the construction are described in detail,and an analysis on structure safety is conducted by numerical method.The results show that:(1)as for the flow-plastic water-rich fracture zone,dense advance support is the most effective measure to prevent large deformation or collapse of surrounding rocks during excavation,a ring of ?51 self-drilling anchor bolts with unit length of 3.5 m are installed between steel arches(with the steel arch interval of 50 cm),that is to say there are 7 layers of advance support for each tunnel section,effectively controlling the rock mass deformation after excava tion,avoiding collapse and clearance invasion of tunnel lining;(2)it is significant to reinforce the surrounding rocks,especially at sidewall and tunnel floor,since it can effectively decrease the integral subsidence of tunnel lining during construction.A combination of jackstone treatment and grouting is adopted to reinforce the surrounding rocks at sidewall and tunnel floor and the effect is much better than that only with grouting;(3)as for the tunnel with explicit external load,the parameters of lining support should be determined by both calculation analysis and engineering ex perience,which will guarantee the safety of tunnel structure and also make it economical and reasonable;(4)as for the two-lane tunnel,three-bench method is taken and the bench length should be shortened as much as possible in order to form an enclosure of primary support in time so as to control the deformation of surrounding rocks better.