基于孔隙压力黏结单元的准脆性材料水力劈裂模拟

Hydraulic fracturing modeling of quasi-brittle materials based on pore pressure cohesive interface elements

传统数值方法对水力劈裂的模拟一般采用预设裂缝扩展路径,且将水流作用等效为压力荷载,难以反映裂缝渗流-开裂耦合效应.采用自编程Python脚本程序批量插入孔隙压力黏结单元,考虑裂缝渗流-开裂耦合作用模拟准脆性材料水力劈裂随机扩展全过程.在对经典理论模型及试验结果模拟验证的基础上,开展含多裂缝均质模型的水力劈裂全过程分析,并进一步建立混凝土细观尺度水力劈裂模型,分析骨料、界面过渡区和基体渗透性对混凝土劈裂全过程的影响.结果表明,本研究模型可以有效模拟准脆性材料水力劈裂失效过程,准脆性材料多缝开裂过程伴随微裂缝的分叉扩展而非光滑的裂缝扩展路径,骨料及界面过渡区影响劈裂扩展路径造成裂缝分叉出现,混凝土基体的渗透性对其抵抗水力劈裂不利并影响失效软化过程.

In traditional numerical methods,pre-defined crack paths are often assumed and flow effects of fluids are often simplified as equivalent pressure loads on the crack when modelling hydraulic fracture,which makes it difficult to reflect the coupling effects of seepage and fracture.In this study,a highly efficient Python code was developed to insert pore pressure cohesive interface elements into the solid finite element mesh,and the coupling mechanism of seepage-fracture was considered to model the complicated hydraulic fracture process in quasi-brittle materials.The effectiveness of the model was validated by the simulations of the classic theoretical model and experimental results.Furthermore,the whole process of hydraulic fracture with multiple pre-existing cracks was simulated,the meso-scale hydraulic fracture model of concrete was established,and the influences of aggregates,interface transition zone and permeability of matrix were analyzed.Results show that the developed model can reliably simulate complicated hydraulic fracture problems of quasi-brittle materials,the multi-crack propagation is accompanied by the bifurcation propagation of micro cracks rather than smooth crack propagation trajectory.The aggregates and interface transition zone affect the fracture trajectory,and the bifurcation of crack is generated.The permeability of concrete matrix affects its resistance of hydraulic fracture and failure softening process.