为研究高填黄土明洞加筋减载的荷载传递规律，采用颗粒流软件模拟高填黄土明洞加筋减载，通过分析洞顶竖向应力、颗粒竖向位移、颗粒间的接触力、格栅的竖向变形和孔隙率等细观参数的变化，从微观角度揭示土工格栅加筋减载明洞减载规律，并进一步研究土工格栅刚度和层数对洞顶减载效果的影响。结果表明： 1）土工格栅的竖向变形和颗粒竖向位移变化形式基本保持一致，格栅的变形依赖于洞顶内外土柱的沉降差； 2）在格栅所能承受的最大变形范围内，内外土柱负的沉降差越大，格栅的拉膜效应越显著，减载效果越好； 3）格栅的刚度和层数对其减载效果均有一定的影响，应根据实际填土高度和填土性质选择适宜刚度和层数的格栅进行减载。

The reinforcement load reduction law for highfilled opencut tunnel is simulated by particle flow code(PFC) software, the microscopic parameters variations of vertical stress on the top of opencut, vertical displacement of particles, contact force, vertical deformation of geogrid and porosity are analyzed. The law of reinforcement load reduction by geogrid is revealed from microscopic aspect, and the influence of intensity and layers of geogrid on unloading effect of top opencut tunnel are further studied. The numerical simulation results indicate that: (1) The vertical deformation of geogrid is consistent with that of particles; the deformation of geogrid depends on the settlement difference between the inner and outer soil column on tunnel roof. (2) Within the maximum deformation range that the grille can withstand, the larger the negative settlement difference between the inner and outer soil column, the more significant the tension membrane effect of the geogrid and the better the load reduction effect. (3) The stiffness and the number of layers of geogrid have a certain impact on its load reduction effect, which should be considered according to height of the filled soil and the nature of the filled soil.