自然营造力作用下岩石单裂纹水力劈裂数值仿真模型

考虑水利水电工程中自然营造力作用下岩石水力劈裂特点,建立裂纹内初始含水量饱和而外界水压增大情况下,裂纹进一步发生水力劈裂的数值仿真模型。在数值模型中,通过半解析半数值方法建立裂纹内水压分布梯度与裂纹张开位移间的耦合关系,不仅简化耦合迭代分析,而且提高计算精度;断裂力学模型采用以Hillerborg黏滞区裂纹模型为基础的COD准则,并引入损伤变量对其开裂准则进行修正;裂纹的扩展采用预置零厚度接触单元的方法巧妙地解决耦合与非线性迭代中裂纹的前进与后退问题。最后,对简单的岩石试件进行水力劈裂过程数值仿真分析,得到的裂纹内水压分布规律与已有的试验结果吻合,证明所建模型是合理的,计算结果是可靠的。

NUMERICAL SIMULATION MODEL OF HYDRAULIC FRACTURING OF ROCK WITH A SINGLE FRACTURE UNDER NATURAL HYDRAULIC POWER

The hydraulic fracturing in fields of water conservancy,hydropower and mining engineering is produced by natural hydraulic power.Its boundary conditions are different from those in artificial hydraulic fracturing applied in fields of petroleum and natural gas engineering.Considering hydraulic fracturing characteristics of natural hydraulic power in the fields of water conservancy and hydropower engineering,a numerical simulation model of hydraulic fracturing of rock with a single fracture initially filled by saturation water is built.It is assumed that the flow in the fracture is the Newtonian fluid without compressibility.It is in accordance with lubrication theory.The flow pattern is one-dimensional laminar flow.The fracture flow is meshed as one-dimensional element.The differential equation of water pressure gradient of fracture inner surface and opening width is induced using semi-analytical and semi-numerical methods.This method simplifies coupling analysis iteration and improves analysis precision.The fracture propagation model employs Hillerborg cohesive zone one model COD criterion modified by damage factor.The interface elements with zero thickness are arranged in possible fracturing zone.Through adding or deducing the number of interface element,the dynamic motions of fracture and procedure iteration process are carried out.Finally,the hydraulic fracturing process of rock sample with a single fracture is simulated.The simulation results are compared with other experimental ones.The inner water pressure distribution law is consistent with experimental one.The rationality of the model and reliability of the calculation results are confirmed.