浅埋隧道围岩压力计算模型修正及应用

Modification and application for ground pressure calculation model in shallow tunnels

以现行规范中浅埋隧道围岩压力计算的力学模型为基础,引入潜在滑移面偏移角的概念,提出潜在滑移面可随岩土体参数变化而偏转的修正计算模型;同时利用水平条分法引入地表边界条件,通过图解法可准确求得滑移角、破裂角、侧阻力与竖向围岩压力。对不同围岩条件下进行算例分析,并通过敏感性分析探讨岩土体抗剪强度指标对块体体积、侧阻力及其分布模式、竖向围岩压力的影响。研究结果表明:在计算假定完全相同情况下,修正模型即蜕化为传统模型;而围岩等级较低时,二者计算结果相近。随着黏聚力和摩擦角的增加,岩土体整体自稳能力增强,可滑动三角形块体体积减小,使其提供的侧阻力合力降低;侧阻力分布模式受重度影响减弱,受抗剪强度指标的影响相对增强,故其分布曲线形心上移;下沉梯形块体体积增大,与减小的侧阻力协同作用,使得竖向围岩压力增加。黏聚力和摩擦角对围岩压力计算结果的影响一致,因此运用修正模型时,也可采用计算摩擦角的等效方式估算浅埋隧道的围岩压力。

Based on the calculation diagram specified by the current codes, the slip angle was introduced and the modified calculation model was proposed, in which the potential slip plane deflects along with the change of parameters. The surface boundary condition was considered by using the horizontal slice method, so that the slip angle, the fracture angle, the lateral resistance and the vertical ground pressure were calculated in a more accurate way by graphical method. The case with different ground conditions was studied. Furthermore, the influences of anti-shear indices on the block volume, the lateral resistance and its distribution pattern, and the vertical ground pressure were discussed through sensitivity analysis. The results show that the calculation results from traditional model and modified model fit each other well. The modified model can be degenerated into the traditional model on the same calculation assumptions. The ground stability is enhanced with the increase of cohesion and friction angle, which reduces the volume of triangle block and the lateral resistance. Meanwhile, the influence of gravity on the distribution pattern of lateral resistance is weakened, and the influence of anti-shear indices is relatively enhanced, which makes the centroid of distribution curve move up. Therefore, the synergistic effect provided by the decreased lateral resistance and the increased volume of trapezoidal block enhances the vertical ground pressure. Cohesion and friction angle affect the calculation of ground pressure in an identical mechanism, so that the equivalent friction angle can also be adopted to calculate the ground pressure of shallow tunnel.