超前区域注浆是煤层底板灰岩水害防治的有效手段，而注浆工程中的劈裂注浆过程是决定注浆效果的关键环节，但由于对受注灰岩地层裂隙起裂机制认识不清，致使劈裂注浆过程中注浆压力、浆液水灰比等参数缺少有效控制，难以保证注浆效果。针对上述问题，利用颗粒元(Particle Flow Code，PFC)数值模拟软件，考虑浆液水灰比、地应力水平、弱面和裂隙的倾角和宽度等因素，开展奥陶系灰岩顶部劈裂注浆数值模拟计算。结果表明：在弱面和裂隙条件下起裂压力均随浆液水灰比(1∶1、2∶1、3∶1)的增大而减小，随最大主应力与最小主应力差值(9、12、15 MPa)的减小而增大，随弱面或裂隙宽度(3、8、15 mm)及其与最大主应力夹角(30°、60°、90°)的增大而减小；起裂裂隙沿平行于最大主应力方向延展；起裂压力值随弱面与基质强度比(0.30、0.03)的减小而减小，当弱面强度较高时，起裂压力大于裂隙条件下的起裂压力，而且沿着基质起裂；当注浆孔置于弱面两端或裂隙中间时，起裂裂隙沿弱面或裂隙的两端起裂，当注浆孔置于弱面中间位置时，起裂裂隙沿中间位置的基质起裂。研究结果有助于底板水害超前区域改造劈裂注浆的有效控制，指导注浆参数的选取，为解放深部煤炭资源提供技术支撑。

The advanced regional grouting is an effective means to prevent and control the water hazard of limestone in coal seam floor, and the fracture grouting projects is a key link to determine the effect of the grouting in floor against water hazard. However, due to the unclear understanding of the fracture initiation mechanism of the injected limestone stratum, the grouting pressure, grout water-cement ratio and other grouting parameters in the process of fracture grouting are not effectively controlled. Thus, it is difficult to guarantee the grouting effect. In order to solve the above problems, numerical simulation calculation was conducted for the fracture grouting in top of Ordovician limestone with the Particle Flow Code (PFC) numerical simulation software, considering the grout water-cement ratio, in-situ stress, and the dip angle and width of weak surface and crack. The results show that: The fracture initiation pressure decreases with the increase of the grout water-cement ratio (1∶1, 2∶1, 3∶1), but increases with the decrease of the difference between the maximum and minimum principal stresses (9, 12 and 15 MPa) under the weak surface and fracture conditions. Besides, the crack initiation pressure decreases with the increase of the width of the weak surface or crack (3, 8, 15 mm) and the angle between the weak surface/crack and the maximum principal stress (30°, 60°, 90°). The initiated cracks propagate along the direction parallel to the maximum principal stress. The fracture initiation pressure decreases with the decrease of strength ratio of weak surface to matrix (0.30, 0.03). In case of weak surface with high strength, the fracture initiation pressure is greater than that under the fracture condition, and the cracks propagate along the matrix. When the grouting hole is located at both ends of the weak surface or in the middle of the crack, the cracks are initiated along the weak surface or at both ends of the crack. When the grouting hole is located in the middle of the weak surface, the cracks propagate along the matrix in the middle position. Generally, the research results are helpful to the effective control of fracture grouting in the advanced regional for floor reconstruction against water hazard, and guide the selection of grouting parameters, thus providing technical support for the development of deep coal resources.