The major principal stress direction of the tunnel is one of the most important factors affecting the stability of an underground tunnel. This paper is devoted to the quantitative analysis of the effect of the major principal stress direction respect to the tunnel long axis on the stability of an underground tunnel. A total of thirty-two loading levels with three physical models combined with the numerical simulation were conducted. The results indicated that, with the decrease of the angle between the major principal stress direction and the long axis of the tunnel, the tunnel becomes more stable. For the load at which cracks begin to occur in the tunnel, when the major principal stress direction is parallel to the tunnel axis, there are no cracks in the tunnel until the load reaches approximately twice as much that of perpendicular. When the major principal stress direction is perpendicular to the tunnel axis, the failure involves spalling. The cracks initially occur at the corner of the tunnel, and then propagate along the sidewall in the form of a parabola. When the major principal stress direction is parallel to the tunnel axis, the failure involves ring-like damages. Cracks appear at the top and bottom of the tunnel, and connect with the cracks on the sidewall. With the increase of the principal stress, the effect of the major principal stress direction increases.

隧道的主要主应力方向是影响地下隧道稳定性的最重要因素之一。本文致力于定量分析主要主应力方向相对于隧道长轴对地下隧道稳定性的影响。结合数值模拟，进行了总共32个载荷水平和三个物理模型的计算。结果表明，随着主主应力方向与隧道长轴之间的夹角的减小，隧道变得更加稳定。对于在隧道中开始出现裂纹的载荷，当主应力方向平行于隧道轴线时，直到载荷达到垂直载荷的两倍时，隧道中才会出现裂纹。当主要主应力方向垂直于隧道轴线时，破坏涉及剥落。裂纹最初发生在隧道的拐角处，然后以抛物线的形式沿着侧壁传播。当主要主应力方向平行于隧道轴线时，破坏涉及环状损坏。裂缝出现在隧道的顶部和底部，并与侧壁上的裂缝相连。随着主应力的增加，主主应力方向的影响增加。失败涉及环状损坏。裂缝出现在隧道的顶部和底部，并与侧壁上的裂缝相连。随着主应力的增加，主主应力方向的影响增加。失败涉及环状损坏。裂缝出现在隧道的顶部和底部，并与侧壁上的裂缝相连。随着主应力的增加，主主应力方向的影响增加。