基于裂纹扩展模型的脆性岩石破裂特征及力学性能研究

为了探究初始微裂纹参数分布对岩石破裂特征及力学性能的影响，进一步系统地了解脆性岩石破裂演化过程，依据线弹性断裂力学理论，建立了非均质性二维细观弹性损伤模型，并运用FLAC^2D数值分析软件，数值模拟研究了单轴压缩条件下不同形态岩石试样的破裂过程。研究结果表明，当初始微裂纹长度和角度服从不同的随机分布时，岩石材料表现出不同的破裂特征，其中初始微裂纹长度和角度均服从正态分布时，岩石破裂区域较完整；初始微裂纹长度或角度服从均匀分布和指数分布时，岩石破裂区域较分散；初始微裂纹角度对于解释脆性岩石单轴抗压试验时岩石试样出现剪切破坏和劈裂破坏的原因具有一定的指导意义，且当初始微裂纹角度均值ɑ=45°时，模型具有最小的峰值强度和轴向最大应变。模型还模拟了脆性岩石单轴抗压试验、巴西劈裂试验和断裂韧度试验的演化过程，模拟结果与试验结果具有较高的一致性。

Study on Fracture Characteristics and Mechanical Properties of Brittle Rock Based on Crack Propagation Model

In order to study the influence of initial microcrack parameter distribution on fracture characteristics and mechanical properties of brittle rocks and further understand systematically the fracture evolution of brittle rocks， a two-dimensional mesoscopic elastic damage model of heterogeneity was established based on the theory of elastic fracture mechanics.The proposed model scheme was implemented through the two dimentional finite difference program FLAC^2D.The zones in the model behave elastically before failure occurs, and lose tensile or shear load bearing capacity at corresponding mode of failure.Microcracks with different length and orientation distributions were defined in the zones of the model.The failure of the zone was controlled by the fracture propagation status of the microcrack inside.A failure criterion was adopted based on the stress intensity factor of the microcrack in each zone.The fracture process of rock specimens with different morphologies under distinct loading conditions was simulated using the proposed numerical model.The influence of the microcrack distributions on both the macroscopic fracture pattern and the mechanical response of the numerical model was analyzed.The results show that when the microcrack lengths and orientations are defined by different distributions，the different macroscopic fracture modes can be resulted.When the microcrack lengths and orientations are defined by normal distribution， failure band with clear shape can be formed.Failure zones are relatively dispersed if the microcrack lengths or orientations obey uniform or exponential distributions. For the reasons of shear failure and splitting failure of rock samples during the uniaxial compression test of brittle rock， the initial microcrack orientation was of guiding significance.When the mean initial microcrack orientation ɑ=45°， the minimum peak strength and axial maximum strain of model were obtained.The fracturing process of brittle rock uniaxial compression test， Brazilian splitting test and fracture toughness test were simulated.Good consistency was obtained with respect to both the mechanical response and fracture patterns.The model is valuable in rendering reliable results for rock mechanical tests which are difficult to realize in the laboratory. The inclusion of the influence of microcracks in simulating mechanical behavior of rock material also provide important insights into the failure process of rock under external load.