落石冲击下拱形明洞结构受力的模型试验研究

为研究落石冲击下拱形明洞结构的受力特点，通过改变落石质量及回填土厚度，利用1∶30缩尺模型试验分析了结构落石冲击所在断面不同部位的横向应变、轴力及弯矩等内力响应最大峰值的大小及分布特征，对各内力最大峰值随回填土厚度的变化趋势进行了分析，最后利用结构变形、弯矩及轴力图，对落石冲击下有回填土拱形明洞结构受力模式进行了总结. 研究结果表明:拱顶部位力学响应最显著，拱肩次之，拱腰及仰拱最小；结构受力形态可描述为拱顶部位轴向受拉、拱肩及以下部位为轴向受压的力学模式；与静力学分析隧道或明洞衬砌结构的荷载-结构模式不同，现行隧道设计规范中按素混凝土偏心受压构件对拱顶结构进行安全检算的方法并不适用于落石冲击工况；回填土厚度的增大有利于结构拱顶、拱肩及仰拱结构的受力，但对拱腰部位影响复杂，在设计时需结合落石规模、边墙形式及回填方式等进行具体分析. 

Experimentation on Stress Analysis of Arch-Shaped Open Tunnel Structure under Rockfall Impaction

In order to study the stress characteristics of the arch-shaped open tunnel structure under rockfall impaction, the magnitude and distribution characteristics of crosswise strain, axial force and moment in different parts of the impaction cross-section of the structure were analysed by a 1∶30 reduced scale model test, with changes of the rockfall mass and the backfill thickness. The trend of maximum internal force peak with backfill thickness was also analysed. Finally, the stress pattern of arched open tunnel structure covered with backfill under rockfall impaction was summarized, in terms of the deformation, moment and axial force of the structure. The results indicate that the mechanical response of the vault is the most significant, followed by the spandrel, inverted arch and the hance. The stress pattern of the structure for the vault is axial tension, and for the spandrel and the lower part is axial compression.This is different from the load-structure mode of the static analysis lining-structure of the tunnel or the open tunnel. Hence safety check and computation of the vault structure cannot be carried out according to the eccentric compression component of plain concrete in the tunnel design code, and other solutions should be devised. The increase of backfill thickness is beneficial to the structure of vault, spandrel and inverted arch, but is not necessarily good for hance, and it needs to be analysed by combining the size of rockfall with the form of side wall and backfill way in the design.