为解决横断山区软岩隧道的大变形问题,本文以云南省昌宁至保山高速公路昌宁隧道为工程背景,采用理论分析、现场试验等方法,从作用机理、支护方案、施工工艺等方面对软岩隧道开展了高预紧力恒阻大变形(NPR)锚索主动支护及关键技术研究。结果表明:被动支护下,隧道围岩节理裂隙发育、黏土矿物含量高、围岩强度低、微观结构存在细小溶蚀孔、结构疏松等是昌宁隧道围岩发生变形破坏的主因;提出了“NPR锚索+PR锚索+“W”钢带+高强柔性网”主动支护技术,并通过现场松动圈测试等试验,确定了NPR锚索、PR锚索等的支护参数;针对极破碎围岩及含水软岩的特殊环境,提出了“先喷后支+复喷”和“锚固端下缘封堵+钢绞线端头加丝”NPR锚索主动支护优化技术;现场试验结果表明,NPR锚索主动控制技术能够有效控制软岩隧道围岩大变形,最大变形量由原来的2 125 mm控制到300 mm以内,保障了隧道支护结构的安全。
To solve the problem of large deformation of soft rock tunnel in Hengduan Mountains, Changning Tunnel of Changning-Baoshan Expressway in Yunnan Province is taken as the engineering background, and adopts the methods of theoretical analysis and field test to carry out the research on active control key technology of NPR cable in soft rock tunnel from the aspects of action mechanism, support scheme and construction technology. The results show that under passive support, the main causes of deformation and failure of surrounding rock in Changning tunnel are the development of joint fissures, high clay mineral content, low strength of surrounding rock, small dissolution pores in microstructure and loose structure. The active support technology of “NPR anchor cable + PR anchor cable + “ W” steel belt + high strength flexible net” is put forward, and the support parameters of NPR cable and PR cable are determined by field loose circle test. Aiming at the special environment of extremely broken surrounding rock and water-bearing soft rock, the optimization technology of NPR cable active support of “spray before support + re-spray” and “lower edge sealing of anchorage end + wire adding of steel strand end” is put forward. The field test results show that the NPR cable active control technology can effectively control the large deformation of soft rock tunnel, and the maximum deformation is controlled from 2 125 mm to 300 mm, which ensures the safety of tunnel support structure.
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