为解决大亮山隧道穿越高地应力膨胀性软岩地层时出现的底鼓灾害和二次衬砌持续压溃问题，采用现场调研、监测试验与数值模拟等手段，开展大变形隧道支护破坏演化机制分析和支护方案优化设计研究。根据隧道病害特征、现场测试试验，提出加深仰拱+打设钢花管+增厚二次衬砌的支护优化方案；结合数值模拟验证支护优化方案的可行性，并将优化后的支护方案在试验段开展工程应用。主要结论如下： 1）隧道底部围岩遇水软化后承载能力显著降低，在未被水侵蚀的拱脚位置产生应力集中现象，上覆围岩压力传递至拱脚的向下荷载与隧道底部围岩膨胀产生的向上荷载在拱脚附近交汇，从而诱发局部剪切隆起破坏； 2）仰拱单侧隆起破坏削弱了二次衬砌水平支撑力，在围岩水平构造应力作用下隧道两腰向洞内挤入变形，二次衬砌内表面压应力较大的拱肩至拱顶范围内出现混凝土压溃和钢筋挤出破坏，二次衬砌破坏后对围岩的水平约束能力进一步丧失，导致塑性区范围显著增大并向仰拱隆起侧的拱肩位置发展，加剧了仰拱隆起变形和二次衬砌破坏趋势； 3）支护方案优化设计主要发挥增强围岩承载能力和改善二次衬砌内力分布的作用，与优化前相比围岩塑性区拉剪破坏范围明显减小，由于水侵蚀隧道底部造成的底鼓和二次衬砌压溃灾害得到有效控制。
When the Daliangshan tunnel
crosses through expansive soft rocks with high geostress, the tunnel bottom
uplifted and the secondary lining continuously collapsed. To address these
issues, field investigation, monitoring experiment, and numerical simulation
methods are employed to analyze the support failure evolution mechanism of
large deformation tunnel and optimize the design of the support scheme. A
support optimization scheme of deepening the inverted arch + laying the steel
flower pipe + thickening the secondary lining is proposed according to the
tunnel disease characteristics and the field test. The feasibility of the
support optimization scheme is validated through numerical simulation, and the
optimized support scheme is applied in the experimental section. Main findings
are as follows: (1) The water-softened
surrounding rock at the arch bottom experiences a marked decline in its bearing
capacity, while stress concentration emerges at the non-eroded arch foot. The convergence of downward loads transmitted from
overburden pressures and upward expansion forces originating from the softened
rock base at the arch bottom culminates in localized shear bulge failure at the
arch foot. (2) The unilateral bulge of the inverted arch diminishes the
horizontal restraint provided by the secondary lining. Consequently, under the
horizontal stress imposed by the surrounding rock, the tunnel′s lateral flanks are compressed inward, leading to concrete crushing
and steel extrusion failures within the arch shoulder to arch crown region,
where internal compressive stresses are relatively high. The subsequent loss of
horizontal confinement in the surrounding rock enhances the plastic zone
extent, particularly towards the arch shoulder on the side of the inverted arch′s uplift, exacerbating both the arch bulge and the failure of the
secondary lining. (3) The optimized support design fundamentally strengthens
the load-bearing capacity of the surrounding rock and
refines the internal force distribution within the secondary lining. After
optimization, a notable reduction is observed in the extent of tensile and
shear failures within the plastic zone of the surrounding rock. Furthermore,
disasters such as bottom bulge and secondary lining collapse, triggered by
water erosion at the arch bottom, are effectively contained, demonstrating the
efficacy of the proposed support enhancement measures.
