滚刀作用下双向应力岩体表面裂纹演变及破岩机理

Chips between cutters are formed by surface and internal crack propagations of the rock in biaxial states. The rock breakage mechanism, considering internal crack propagation, has been comprehensively studied. However, the surface crack propagation and the corresponding rock breakage mechanism lack systematic study. Therefore, the proposed project aims to study the characteristics of the rock breakages affected by the surface crack propagation, and to investigate the conditions for the effective breakages, caused by surface crack propagation, when various external or internal factors are considered. The evolution characteristics of the surface cracks are obtained by conducting indentation tests in biaxial states, then, with the spatial morphologies of the chips and the grooves between cutters, we study the relation between the surface crack propagation and chip formation. In addition, we obtain the stress distributions of the crushed and the plastic zones under the cutters, using theoretical and numerical methods. Then, the evolution of the mechanical field and the law of the energy release will be clarified by analyzing the dynamic stress evolution at crack tips. With the above analyses, we establish a compounded rock breakage model, considering surface crack propagation and characterized by compressive-shear and tensile-shear failures. Moreover, we study the main influencing factors and the effective rock breakage conditions by analyzing the surface crack propagation and breakage characteristics when various internal and external factors are considered. The results of the proposed project may further contribute to understanding rock breakage mechanism, simultaneously, may provide guidance for the designs of cutters and cutterheads.

处于双向应力条件下的岩体，在滚刀作用下形成的破碎体由表面及内部裂纹共同决定。目前，基于内部裂纹演变的破岩机理已有深入研究，而对表面裂纹演变及其破岩机理缺乏系统研究。本项目围绕表面裂纹空间扩展演变形成破碎体的过程特性和岩体内、外部因素影响下表面裂纹有效形成破碎体的条件两个科学问题展开。通过试验研究捕获双向应力条件下表面裂纹的演变扩展特性，结合破碎体及破碎坑三维形貌，研究表面裂纹扩展演变形成破碎体的机理；采用理论分析与数值模拟获得滚刀下方密实核与塑性区的应力分布特性，分析表面裂纹扩展过程中尖端应力动态演变，阐明岩体破碎过程中各物理场力学演变和裂纹能量释放规律，构建双向应力条件下考虑岩体表面裂纹的压剪，拉剪复合断裂破岩模型；获得各类岩体内、外部因素作用下表面裂纹演变及岩体破碎特性，研究主要影响因素及有效破碎的条件。该项目结果能进一步揭示滚刀破岩机理，同时可为TBM滚刀及刀盘设计提供参考。

常截面（CCS）滚刀是安装在隧道掘进机（TBM）刀盘上的主要破岩构件，但在复杂地质条件下，CCS滚刀常出现磨损大，破岩效率低等问题，导致各类隧洞掘进速度缓慢，换刀工程费用极大增加。为此，本项目围“绕表面裂纹空间扩展演变形成破碎体的过程特性及岩体内、外部因素影响下表面裂纹有效形成破碎体的条件”这两个关键科学问题，首先对不同截面形式滚刀作用下裂纹扩展演变与其密实核及塑性区外边界应力集中，消散规律进行研究。其次，预制了以CCS滚刀为主体的含切削齿的组合滚刀，研究组合滚刀作用下岩体表面裂纹起裂，扩展形成刀间破碎体的过程特性。第三，开展室内试验探究了刀间距，侵深等因素对组合滚刀作用下岩体表面裂纹扩展演变及破碎体形成的影响机制。关于不同截面形式滚刀致裂机理研究表明楔形截面滚刀有利于平行于侵入方向的中间裂纹产生，而球形及常截面滚刀易于形成侧向裂纹。其次，含不同切削齿的组合滚刀破岩试验表明，切削齿在破岩过程中易于形成刀间表面裂纹，而该表面裂纹与内部裂纹的相互切割可以提升滚刀间岩体破碎程度。第三，刀间距及侵深等因素直接影响CCS及含切削齿滚刀作用下表面裂纹的形成，较大侵深有利于切削齿形成表面裂纹与岩体内部裂纹的相互切割，刀间破碎程度能得到较大提升，但破岩能量增幅较小，因此，破岩效率提升平均值达27%。该项目研究结果能为滚刀设计提供一定指导，能有助于解决TBM滚刀破岩效率低下，磨损高等工程问题。