荷载作用下多裂隙煤体力学特性与起裂角研究

Mechanical properties and crack initiation angle of multi-fractured coal under load

为研究静态加载条件下裂隙几何位置及相互作用机制对煤体力学行为的影响,采用数字图像相关方法作为全场观测手段,以原煤预制不同位置分布下的三裂隙试样为研究对象,利用MTS816岩石伺服试验机进行单轴压缩试验,并结合颗粒流程序研究了裂隙不同位置分布状态下多裂隙煤体的力学特性、裂纹演化规律及破坏特征。与此同时,基于断裂力学理论讨论了T应力对煤体多裂隙尖端的影响形式及适用性。研究结果表明:当裂隙由平行共线分布向平行重叠分布过度时,煤样的宏观强度具有逐渐增强的现象;裂隙的分布形式会影响煤体的承压状态,当裂隙间距离较远时,应力场中应力薄弱区会独立存在,并随着压力增加逐渐扩展融合;而当裂隙趋于重叠分布时,应力集中区和薄弱区都会各自形成统一的受力整体,相互影响。多裂隙共线或偏置分布时,裂隙面以剪应力为主,拉应力为辅的驱动方式导致煤样发生拉剪复合破坏,而当多裂隙趋于重叠分布时,裂隙面上的剪应力转化为岩桥区拉应力,从而形成以拉应力为主导的方式驱动试样发生拉伸破坏。考虑T应力影响时,包含3个T应力分量(Tx,Ty和Txy)的起裂角理论预测值更适用于压剪应力状态下有限板多裂隙尖端裂纹扩展角度方面研究。

This study investigates the influence of fracture geometry and interaction mechanisms on the mechanical behavior of coal under static loading conditions.The digital image correlation method is used as a full-field observation technique,and uniaxial compression tests are conducted on three-crack samples of raw coal prefabricated at different positions using an MTS816 rock servo testing machine.The mechanical properties,crack evolution,and failure characteristics of multi-fractured coal under different position distribution conditions are studied by combining particle flow simulations.Based on the fracture mechanics theory,the influence and applicability of T stress on the multi-fracture tip of coal are discussed.The results show that as the fractures transition from parallel collinear distribution to parallel overlapping distribution,the macroscopic strength of coal samples gradually increases.The distribution form of the fracture affects the pressure state of the coal body,where widely spaced fractures create independent stress weak zones that expand and coalesce as stress increases.Conversely,when fractures tend to overlap,stress concentration areas and weak areas form a unified force system that influences each other.When multiple fractures are collinear or offset distributed,shear stress dominates the fracture surface,and the driving mode supplemented by tensile stress leads to tensile-shear composite failure of coal samples.However,when fractures tend to overlap,shear stress on the fracture surface converts to tensile stress in the rock bridge area,resulting in tensile failure dominated by tensile stress.When considering the influence of T stress,the theoretical prediction value of the crack angle containing three T stress components(Tx,Ty and Txy)is found to be more suitable for studying crack growth angle of multiple fracture tips of finite plate subjected to compression shear stress.