大断面隧道仰拱底鼓破坏模式

仰拱作为隧道重要的组成部分，其底鼓变形是影响路面及轨道平顺性的关键因素，与车辆的安全运行息息相关，为确定大断面隧道仰拱底鼓的基本破坏模式，弄清仰拱底鼓产生机理，采用室内模型试验与扩展有限元数值模拟相结合的方法，对不同加载模式下仰拱底鼓的基本破坏模式进行研究，将试验结果与扩展有限元结果进行比较，验证试验中破坏模式的准确性。将围岩压力分为底部受力占优，侧面受力占优以及底部和侧面受力同时占优3种情况，以确保模型试验加载方式的可靠性，并对其破坏机理进行分析。研究结果表明：大断面隧道仰拱底鼓破坏的基本模式可以分为U-W形破坏、U-LJ形破坏以及U-H形破坏3种；U-W形底鼓时仰拱底部承受较大的顶升力，引起仰拱隆起变形，以仰拱中心受弯破坏为主，仰拱两侧拱腰处与上部衬砌相连，对其隆起有一定的阻碍作用，导致中心部位隆起速度明显高于两侧，最终形成W形的破坏形态；U-LJ形破坏时仰拱承受较大的水平轴力，导致仰拱出现剪切破坏，最终形成W形的破坏形态；U-H形破坏时仰拱在底部和侧面荷载的挤压下，仰拱与边墙的连接部位受剪破坏，无法有效传递轴力，最终导致仰拱与边墙脱开；仰拱中心以及仰拱与边墙连接部位为仰拱的易损薄弱位置；研究成果可为隧道仰拱结构的设计和施工提供理论依据，对保证隧道的安全运营具有重要意义。

Failure Modes of Floor Heave in Large Section Tunnel Invert

An invert is an important part of a tunnel, and the deformation of the tunnel invert is a key factor that affects track regularity and is closely related to the safety of tunnel operations. To determine the failure modes of floor heave in a large section tunnel invert and its mechanism, model tests and extended finite element method analyses were conducted for different loading methods. The surrounding rock pressure was divided into three components for analysis:dominant forces in the bottom, dominant forces in the flank, and simultaneous dominant forces in the bottom and flank. This guaranteed the reliability of the loading mode in the model test. The results show that the basic failure modes of floor heave of the invert in the large section tunnel are of the U-W, U-LJ, and U-H crack types. The U-W crack type is mainly characterized by bending failure in the middle span. The bottom is subjected to a large supporting force that leads to uplift deformation, and the sides of the tunnel are connected to the lining, which has an inhibition effect on the uplift deformation, eventually leading to the U-W crack type. In the U-LJ crack type, the large section tunnel invert receives a large horizontal axial force, which leads to shearing failure of the tunnel invert. The U-H crack type generally emerges when the tunnel invert is subjected to simultaneous bottom and side loading; the connection between the tunnel invert and side wall is broken by the shearing and cannot effectively transmit axial force, thus causing the tunnel invert and side wall to eventually disengage. It is found that the center of the tunnel invert and the connection between the invert and side wall are the weak portions of the invert. Furthermore, the accuracies of the basic failure modes are verified by comparisons of the calculated results with those from the extended finite element analyses. The research results in this study can provide a theoretical basis for the design and construction of tunnel inverts and may be of great significance to ensure the safety of tunnel operations.