衬砌背后双空洞影响下隧道结构的安全状态分析

衬砌背后多空洞的存在使隧道结构受力状态更加复杂,极易引起结构开裂并直接影响到隧道结构的安全性。针对Ⅳ级围岩两车道公路隧道,采用数值模拟和模型试验分别研究拱顶或拱肩背后存在双空洞条件下隧道结构的安全状态。数值模拟结果表明:衬砌背后双空洞的存在,显著改变了隧道结构内力分布,恶化了结构受力状态;空洞尺寸增大会导致隧道结构轴力整体降低,并使空洞范围内及两空洞之间的隧道结构弯矩明显增大;两空洞间隧道结构各截面安全系数较无空洞时显著降低,并表现出随空洞尺寸增加而逐渐降低的趋势,该区域也是隧道结构安全性评价重点部位;拱肩衬砌背后存在双空洞时,其对结构截面安全系数的影响较拱顶和拱肩分别存在空洞的情况更大。模型试验得到的空洞对衬砌结构安全系数影响规律与数值模拟结果基本一致,并获得了双空洞作用下衬砌结构的破坏演化规律。研究成果可为隧道衬砌背后空洞的致灾机制和灾变控制研究提供参考和借鉴。

Effect of double voids behind lining on safety state of tunnel structures

The existence of multiple-voids behind the lining leads to a more complicated stress state of the tunnel structures, which can easily cause the structural cracking and directly affect the safety of the tunnel structures. Based on a two-lane highway tunnel with the IV-class surrounding rock, numerical simulations and model tests are performed to study the safety state of tunnel structures under the influence of double voids behind the lining. The results of numerical simulation indicate that the existence of the double voids significantly changes the distribution of the internal forces in the tunnel structures, and worsens the stress state of the structures. The increase of the range of the void leads to the decrease of the axial forces of the whole tunnel structures, and makes the bending moments of the tunnel structures near the two voids obviously increase. The safety factor of each cross section of the tunnel structures between two voids obviously decreases compared with that in the situation without void. And it presents the trend that the safety factors gradually decrease with the increase of the range of the void. The region between two voids is the key part for security evaluation and improvement of the tunnel structures. When the double voids exist behind the lining of tunnel shoulders, it has a larger influence on the structural safety factors than the situation that the vault and shoulder of tunnel have the voids behind the lining respectively. The effects of voids on structural safety factors obtained by model tests agree well with the results of numerical simulation, and the failure evolution processes of the tunnel structures affected by double voids are also acquired by model tests. The results obtained in this study may provide useful reference for studying the failure mechanisms and safety control techniques of tunnel structures with voids behind the lining.