为控制梦笔山隧道施工过程中围岩的大变形，避免出现掌子面垮塌、围岩变形侵限、初期支护开裂掉块、钢架扭曲失效等问题，总结梦笔山隧道围岩大变形的发展特征，深入分析围岩大变形的作用机制和产生原因，结合隧道地质条件和变形特征，分别从超前预报和超前支护、隧道开挖方法、合理的预留变形量以及隧道支护参数等方面提出相应的控制措施，并通过隧道变形监测验证控制措施的有效性。研究结果表明： 1）梦笔山隧道围岩大变形主要表现为掌子面垮塌、围岩变形发展迅速、水平收敛显著、进出口段围岩变形突出等特征，特殊的地质构造、软弱的岩性和局部发育的地下水环境是导致梦笔山隧道围岩大变形的主要原因； 2）根据围岩变化特征和实际施工情况，采用上下台阶预留核心土法能够尽量减小隧道开挖扰动，并充分释放围岩内部应力，配合合理的预留变形量和恰当的隧道支护结构，能够将隧道水平收敛和拱顶沉降累计值分别控制在400 mm和100 mm以内，[JP2]大大降低围岩侵限的风险； 3）隧道围岩大变形的控制应当在工程实践中找到合理的施工方法、适当的预留变形量以及适宜的支护结构和支护时机。
The large deformation of the surrounding rocks during
the construction of Mengbishan tunnel led to collapse of the tunnel face,
deformation of the surrounding rock that intruding limit, cracking and falling
of the primary support, and twisting and failure of steel frame. Therefore, the
development characteristics of large deformation of the surrounding rocks in
Mengbishan tunnel are summarized, and the mechanism and causes of large deformation
of the surrounding rocks are analyzed. Furthermore, countermeasures for
controlling large deformation of surrounding rocks are proposed from the
aspects of advance geological prediction, advance support, excavation measures,
rational reserved deformation, and support parameters based on tunnel
geological conditions and deformation characteristics. These countermeasures
are validated through field monitoring. The results reveal the following: (1)
The large deformation of the surrounding rock in Mengbishan tunnel is mainly
characterized by collapse of the tunnel face, rapid development of the
surrounding rock deformation, significant horizontal convergence, and prominent
deformation of the surrounding rock in the entrance and exit sections, which is
mainly inducted by special geological structures, weak lithology, and developed
groundwater. (2) According to the characteristics of the surrounding rock and
the actual construction conditions, the two-bench reserved core soil method can
minimize the disturbance of tunnel excavation and fully release the internal
stress of the surrounding rock. A reasonable increase in the amount of reserved
deformation and proper tunnel support structure can control the tunnel
horizontal convergence and arch settlement cumulative value within 400
mm and 100 mm, respectively, greatly reducing the risk
of the encroachment of the surrounding rock. (3) The control of large
deformation of tunnel surrounding rock should focus on reasonable construction
methods, appropriate amount of reserved deformation, appropriate support
structure, and support timing in engineering practice.
