考虑主应力偏转的土体浅埋隧道支护压力研究

传统方法计算浅埋隧道支护压力时,未考虑上覆土体主应力偏转过程,与实际情况不符且计算结果不准确。为真实分析和计算浅埋隧道支护压力,以砂土为研究对象,首先概括浅埋隧道围岩破坏模式,在此基础上分析隧道上覆土体主应力偏转过程和应力状态,得到水平微分土层平均竖向压力与侧向压力和层间平均剪切力的定量关系,进而建立水平微分土层受力平衡方程求解上覆土体竖向压力。最后以隧道侧面滑移土体为对象,通过受力平衡方程求解获得支护压力表达式。新方法考虑了上覆土体主应力真实偏转过程,较传统方法更符合实际,研究结果表明:距离隧道顶部中心线越远,水平正应力与大主应力比值越小;随着土体内摩擦角的增大,竖直正应力与大主应力比值呈现先减小后增大的规律。与模型试验结果对比表明:当隧道埋深较浅时,新方法计算所得支护压力与模型试验结果高度吻合,优于不考虑主应力偏转方法计算结果和半经验性的Terzaghi方法计算结果,从而验证了该方法的有效性,可为浅埋隧道支护设计提供一定理论依据。

Theoretical study on earth pressure on shallow tunnel considering principal stress rotation

The traditional analytical methods for calculating the earth pressure on shallow tunnel are irrespective of the principal stress rotation, and do not reveal the real stress state of soils, and thus result in inaccurate values. A new quantitative method is proposed to acquire the earth pressure on shallow tunnel in sandy soil considering the principal stress rotation. The rotation process and the stress state are firstly analyzed based on the generalized collapse mode for surrounding soil. To obtain the vertical pressure on overlying soil, the equilibrium equation for the horizontal differential layer is established, considering the corresponding relationship among the lateral interlaminar stress, average interlaminar stress and average vertical stress. Eventually the earth pressure is derived by the equilibrium equation for the lateral soils of tunnel. The results show that the ratio of vertical to major principal stress decreases with the increase of the distance to center line, and it presents a decreasing-to-increasing trend with the increase of the internal friction angle. The values of earth pressure calculated by the proposed method fit well with the experimental results when the tunnel is shallow. The new method is even superior to the method irrespective of the principal stress rotation and Terzaghi’s semi-empirical method. The accuracy of the proposed method is validated. It may provide a theoretical basis for the design of shallow tunnel.