为解决高地应力偏压断层隧道建设过程中初期支护非对称大变形问题，依托云南省孟勐高速公路南朗山一号隧道开展大变形灾害处置控制技术研究，根据现场监测数据及掌子面揭露情况分析隧道偏压大变形原因，提出采用双层初期支护控制隧道非对称大变形，利用数值模拟对双层初期支护施作时机进行优化设计。研究结果表明： 1）由现场监测数据和初期支护破坏情况可知，隧道采用原支护方案无法抵抗不均匀且巨大的围岩压力，围岩软弱夹层滑移致使隧道发生偏压大变形灾害，滑移主要在软弱夹层完全暴露时发生，导致隧道左肩发生局部弯曲破坏，右侧拱腰出现局部剪切变形破坏； 2）采用双层初期支护方案时，适当推迟第2层初期支护的支护时机，可以有效改善隧道偏压问题，但是第2层初期支护滞后距离过大也会导致隧道变形收敛过大、初期支护屈服失效等问题，建议第2层初期支护滞后第1层初期支护2 m施作； 3）优化后的双层初期支护有效控制了围岩的剪切滑移破坏，隧道拱顶沉降和水平收敛均满足变形要求，隧道两侧变形差异明显减小，围岩偏压问题得到显著控制。
The primary supports of
tunnels crossing asymmetrical-pressurized
faults are prone to asymmetric large deformation during construction. In this
study, a case study is conducted on the Nanlangshan No.1 tunnel of the Menglian-Menghai expressway in Yunnan, China, and large deformation
treatments and control measures are analyzed. Further, the causes for
asymmetric large deformation of the tunnel are determined according field
measuring data and revealed tunnel face conditions, and the double-layer primary support is proposed to control asymmetric large
deformation. Finally, the operation timing of the double-layer primary support is optimized using numerical simulation
method. The results reveal the following: (1) The on-site
monitoring data and the primary support failure situation show that the
original support method cannot withstand the great and uneven surrounding rock
pressure, and the slip of the weak interlayer of surrounding rock causes
asymmetric large deformation to the tunnel. The slip mainly occurs when the
weak interlayer is completely exposed, resulting in local bending failure of
the tunnel′s left shoulder and local shear deformation
failure of the right arch waist. (2) When applying double-layer primary support, properly delaying the timing of the second-layer primary support effectively lowers the tunnel asymmetrical
pressure. However, excessive lag distance of the second-layer primary support will lead to excessive tunnel deformation
convergence and yield failure of the primary support. A 2 m lag distance is
recommended for the second- and the first-layer primary supports. (3) The optimized double-layer primary support effectively controls the shearing slip failure
of surrounding rock, the tunnel arch settlement and horizontal convergence are
controlled within required values, and the deformation difference between the
two sides of the tunnel is significantly reduced, showing that the asymmetrical
pressure of surrounding rock is significantly minimized.
