边坡岩体内部岩桥对边坡稳定性起控制作用,而边坡岩桥破坏由于受开挖速度的影响会产生加载速率效应,探究边坡内部岩桥在加载速率影响下的变形破坏特征和裂隙扩展机制具有重要意义。通过对类岩石材料试样端部预制裂隙以形成中部岩桥,结合数字图像相关技术,分析了不同加载速率下不同岩桥长度试样破坏特征和裂隙起裂、扩展、贯通规律,并利用断裂力学理论揭示了岩桥裂隙扩展机理。结果表明:应力-应变曲线呈现“峰后波动”和“应力陡降”特征;随加载速率的增加,峰值强度增大,峰值位移减小;得出5种裂隙扩展破坏类型,分别是①上裂隙贯通下端面、②岩桥贯通、③下裂隙贯通左端面、④下裂隙贯通下端面、⑤下裂隙贯通上端面;试样破坏时裂隙数量随加载速率的增大而减少,且试样裂隙首先从下部裂隙尖端起裂;推导了单轴压缩条件下考虑闭合效应的裂隙尖端应力强度因子表达式,起裂角理论计算与试验实测结果在误差允许范围内;岩桥试样表面应变场的变化随加载速率的增大而增大,且试样破坏是由前期损伤累积所导致的。研究成果可为揭示不同加载速率下岩质边坡内部的变形破坏机制、分析围岩稳定性提供理论依据。

The rock bridge in rock mass controls the stability of slope. The failure of rock bridge generates loading rate effect due to the influence of excavation speed. It is of great significance to explore the deformation and failure characteristics and crack propagation mechanism of rock bridge in slope under the influence of loading rate. By prefabricating cracks at the end of rock-like material, we prepared test specimens with middle rock bridge and examined the failure characteristics, crack initiation, propagation and penetration laws of specimens with different rock bridge lengths under varying loading rates with the aid of digital imaging. The crack propagation mechanism was also revealed in line with the theory of fracture mechanics. Results manifested that: (1) The stress-strain curve displayed post-peak fluctuation and stress slump characteristics. With the rising of loading rate, peak strength swelled whereas peak displacement shrinks. (2) Five patterns of crack propagation were identified: the upper crack ran through the lower end face; the rock bridge penetrated through; the lower crack ran through the left end face; the lower crack ran through the lower end face; and the lower crack ran through the upper end face. (3) During the failure of specimen, the number of cracks declined with the rising of loading rate. Cracks started from the tip of the lower crack. (4) The expression of stress intensity factor at crack tip considering closure effect under uniaxial compression was derived, and the theoretical calculation and experimental results of crack initiation angle were both within the allowable range of error. (5) The change of surface strain field of specimen intensified with the rising of loading rate, and the failure of sample was caused by the accumulation of damage in the early stage.