单轴压缩条件下锚杆影响脆性岩体破裂的细观机制

锚杆支护系统是控制深部脆性围岩动力灾害的重要措施,但锚固理论研究仍滞后,锚杆支护下的脆性岩体破坏问题困扰着深部岩体工程实践。根据实际工程中锚杆支护下脆性围岩的浅表局部破坏特点,通过室内相似模型试验研究单轴压缩条件下锚杆杆径影响完整脆性岩体的破坏特性,试验表明,锚杆杆径对脆性岩体弹性模量和强度的提升存在最优匹配的特点,一味强调增大锚杆直径并不能达到理想的围岩控制效果;锚杆改变了脆性岩体单轴压缩破坏模式,宏观上由劈裂破坏转为剪切破坏,杆径对试样剪切破坏的程度有所影响。从细观角度,建立了含两条固有主裂纹的裂纹扩展分析模型,加锚试样单轴压缩破裂模式的改变,可以归结为锚杆锚固止裂效应对试样内部裂纹扩展的抑制作用,使翼裂纹与主裂纹长度比η变小。根据最易开裂角度ζ的计算结果,翼裂纹较长时,翼裂纹朝外载作用方向扩展,产生劈裂破坏,翼裂纹较短时,翼裂纹偏离外载作用方向扩展,产生剪切破坏。从细观上很好地解释了锚杆改变脆性岩体破裂模式的作用机制。

Meso-mechanism of rock failure influenced by bolt anchorage under uniaxial compression loading

As an important support method, the bolt anchoring system is widely used to control the dynamic disasters of deep brittle surrounding rock, but deep rock engineering practices have been beset by the failure of brittle rock with bolt support because the researches on anchorage theories still lag behind. Based on the failure characteristics of brittle surrounding rock with bolt support in practical engineering, such as shallow surface damage and local damage, uniaxial compression fractures of intact brittle specimens influenced by bolts with different diameters are studied by means of laboratory similarity model tests. The test results show that the relationship between bolt diameters and the promotion of the elastic modulus and strength of brittle rock should be matched optimally, and only increasing the bolt diameter can not control ideally the brittle surrounding rock. Also, bolt anchorage can change the uniaxial compression failure mode of brittle specimens, macroscopically, the splitting failure can be transformed into shear one, and the extent of shear failure is determined by the bolt diameters as well. From the angle of meso-scale mechanism, the crack propagation model with two main internal cracks is established to analyze the fracture change of anchored specimens, and its main factor can be attributed to the inhibition effect on the propagation of internal cracks influenced by the bolt anchorage which decreases the length ratio η of the wing crack to the main crack. According to the calculated results of most-easily-cracking angle ζ, the long wing crack wing extends towards the loading direction which mainly induces its splitting failure, conversely, the short wing crack deviates from the loading direction which mainly causes its shear failure. The fracture mechanism of anchored brittle specimens can be revealed preferably in the view of meso-scale.