单轴压缩条件下含双圆孔类岩石试样力学特性的细观研究

圆孔作为一种典型的岩石缺陷,对岩石的力学特性具有重要影响。采用室内试验及PFC2D程序,构建含双圆孔类岩石试样并对其进行单轴压缩试验,研究其不同圆孔间距、倾角组合条件下的强度、裂纹模式及破裂孕育演化特征。研究表明:(1)当间距不变时,随倾角的增大,试样单轴抗压强度呈先减小后增大的趋势,且在倾角为45°~60°时达到最低单轴抗压强度;当倾角为90°恒定时,随间距的增大,试样单轴抗压强度呈先增大后减小的趋势,且在间距为40 mm左右时达到最大单轴抗压强度。(2)试样产生的裂纹类型可分为I型(张拉型)裂纹、II型(剪切型)裂纹、III型(混合型)裂纹等三类。当孔距较近时,随倾角的增大,圆孔间裂纹类型逐渐由III型裂纹转变为II型裂纹,两圆孔靠近加载端部一侧的孔壁逐渐产生I型裂纹,靠近试样两侧边界处的孔壁始终会产生II型裂纹。当倾角为90°恒定时,随间距的增大,两孔间相互作用减弱,但两圆孔靠近加载端部一侧及靠近试样两侧边界处的孔壁,始终分别产生I型裂纹和II型裂纹。(3)两孔间岩桥连线上的II型裂纹首先产生,其次在圆孔靠近加载端部一侧的孔壁产生I型裂纹,最后在圆孔靠近试样两侧边界处的孔壁产生II型裂纹。通常构成II型裂纹的声发射事件破裂强度,高于构成I型裂纹的声发射事件破裂强度。

Mesoscopic mechanical properties of rock-like material containing two circular holes under uniaxial compression

As a kind of typical flaw，circular hole plays a significant role on the mechanical properties of rock. Specimens containing two circular holes were constructed and subjected to uniaxial compression based on lab experiment and two dimensional particle flow code(PFC2D). The effect of the distance between holes and the dip angle on the strength，fracture mode and crack development of rock were investigated in detail. With the increase of the dip angel，the uniaxial compressive strength of specimens decreases first then increases. The uniaxial compressive strength reaches the minimum value when the dip angle equals to 45° to 60°. When the dip angle equals to 90°，the uniaxial compressive strength of specimen increases first and then decreases with the increase of the distance between the holes，and reaches the maximum value when the distance between holes equals to 40 mm approximately. The fractures generated in the specimen can be classified into three modes，namely mode I (tensile fracture)，mode II (shear fracture) and mode III (mixed fracture). When the distance between the holes is small，with the increase of dip angle，the fracture mode between the holes changes from mode III to mode II gradually, while on the hole walls adjacent to loading part, mode I fracture occurs. However，mode II fracture always occurs on the hole walls adjacent to the side boundaries of specimen. When the dip angle equals to 90°，the interaction between two holes weakens with the increase of the distance between holes，however，the mode I fracture occurs on the hole walls adjacent to loading part and the mode II fracture occurs on the hole walls adjacent to the side boundaries all the time. The mode II fracture firstly initiates on the rock bridge between two holes，and then mode I fracture generates on the hole walls adjacent to loading part，and finally mode II fracture occurs on the hole walls adjacent to the side boundaries. Generally，the magnitude of acoustic emission (AE) from the mode I fracture is higher than that from the mode II fracture.