基于裂纹扩展模型的深部硐室围岩致裂规律

根据岩体的非均匀性和存在初始裂纹的特征,在二维有限差分程序中建立了非均质体二维模型,并在模型中考虑初始裂纹的影响,利用程序中的自带编译语言,实现了服从不同分布的初始裂纹的长度和角度的赋值。在模型中,利用亚临界裂纹扩展理论描述与时间相关的裂纹亚临界扩展过程,计算过程可体现裂纹扩展的时间效应,从而实现对所模拟结构的寿命预测。模型中裂纹的扩展方式假定为形成翼型裂纹的形式,利用翼型裂纹的简化模型对裂纹的扩展尺寸,应力强度因子等参数进行计算。在每一计算步中,每个单元中的裂纹扩展方向与该时刻单元所受应力情况相关,应力强度因子与该单元所受应力大小及翼型裂纹简化长度相关。利用该模型对高地应力条件下孔洞开挖卸荷导致围岩破坏的过程进行模拟,分析了深部岩体开挖导致的围岩破坏规律,对不同的孔洞形状和初始裂纹的分布情况分别进行了分析,计算结果显示了非连续破裂的形成与初始裂纹角度分布的关系:分区破裂的表现形态与初始裂纹和最大压应力的夹角相关,并且不同初始裂纹角度均值也会导致围岩破裂时间不同。通过建立的多种孔洞形状开挖模型,对不同孔洞形状围岩破裂形态及破坏时间的规律进行总结,发现相同计算步数内方形孔洞周边围岩处破坏单元数量最多,圆形孔洞周边围岩破坏单元数量最少。研究结果证实了裂纹的分布对孔洞周边围岩破坏形态的影响,对裂纹扩展的时间效应的分析可实现对围岩破坏程度和范围的预测,可为深部高地应力条件下诱导致裂非爆连续开采的实施时间和方式提供指导。

Fracture patterns induced by deep underground excavation based on a crack propagation model

A two-dimensional model is established considering the heterogeneity and the existence of initial cracks of rock materials based on a two dimensional finite difference code.Using the inherent compiling language,the different distributions of the initial cracks’ lengths and orientations are implemented in each zone of the numerical model.The crack propagation rate is described by the subcritical crack growth theory,thus allowing for the analysis of the time effect of the crack propagation and lifetime prediction of the model.It is assumed in the model that the crack propagates forming wing crack.And a simplified wing crack model is adopted for the calculation of the crack length and stress intensity factors.In each calculation step,the crack propagation direction is influenced by the stress condition the zone is subjected to,and the stress intensity factor of the crack is controlled by the stresses and the length of the simplified wing crack.The model is used to simulate the failure process of surrounding rock under unloading of high geo-stress due to excavations.The fracture pattern in the surrounding rock due to excavations is analyzed,and the influence of different shape of the excavation and initial crack distributions is also discussed.The simulation results present the relation between the formation of non-continuous disintegration and the initial crack orientation distributions.The fracture pattern is affected by the angle between the initial crack and the maximum compressive stress.The fracture time of surrounding rock is also influenced by the mean value of initial crack orientations.The fracture patterns and failure time of surrounding rock with different excavation shapes are studied using the numerical model.According to the model with the different shapes of the excavation,within the same calculation stages,the most failure zones are found around square shaped excavations and the lease failure zones are found around circle excavations.The calculation result verified the influence of the distribution of the initial cracks on the fracture patterns of the surrounding rock of excavations,and the time effect in the crack propagation process can allow for the prediction of the extend and scope of failure of the surrounding rock.The results can provide information and guide the applications of the induced fracturing and non-explosive continuous mining in deep excavation sites under high geo-stresses.