坑道施工中，超挖回填材料性能对衬砌的受力分布有较大影响。基于FLAC 3D有限差分数值计算软件，模拟坑道开挖施工，通过改变回填层的弹性模量和厚度，分析了不同回填介质对衬砌结构弯矩和位移的影响，并比较了不同围岩级别对衬砌结构的弯矩影响。计算结果表明： 1）拱顶、侧墙和底板的最大弯矩随弹性模量的增大而减小，弯矩开始降幅较大，但最终趋于平缓；拱顶、侧墙和底板的最大弯矩随回填层厚度的增大而增大，几乎成线性增加。2）拱顶和底板的最大位移随弹性模量的增大而增大，侧墙反之；拱顶和侧墙的最大位移随回填层厚度的增大而增大，底板则基本保持不变。

In tunnel construction, overbreak backfill material has great influence on the distribution of the internal force of the tunnel lining. In the paper, the tunnel excavation is simulated on basis of FLAC 3D finite difference numerical software and the influence of different backfill materials on the bending moment and displacement of the lining structure is analyzed by changing the elastic modulus and the backfill layer thickness. The impact of different surrounding rock grades on the bending moment of the lining structure is also compared. The results show that the maximum bending moment of the crown, sidewall and floor slab decreases as the elastic modulus increases, and it decreases dramatically at first and starts faster and smaller, and tends to decrease gently in the end; the maximum bending moment of the crown, sidewall and floor slab increases almost in linear as the thickness of the backfill layer increases; The maximum displacement of the crown and floor slab increases as the elastic modulus increases, however, the maximum displacement of the sidewall is just on the contrary; The maximum displacement of the crown and sidewall increases as the thickness of the backfill layer increases, however, the maximum displacement of the floor slab remains almost stable.