加载速率对砂岩宏细观力学性质影响研究

Effects of Loading Rate on Macroscopic and Mesoscopic Mechanical Properties of Sandstone

为了研究加载速率对砂岩宏细观力学性质的影响,建立了基于平行粘结模型和加入黏性阻尼的线性接触模型的三维颗粒流模型,提出了砂岩黏性的离散单元分析方法,利用控制变量法和试错法,进行模型细观参数的标定工作,并通过自编Fish语言对颗粒流模型进行了多组不同加载速率的压缩试验模拟。研究结果表明,加载速率减小,砂岩的峰值强度、弹性模量、泊松比、内摩擦角均减小,轴向黏塑性应变和黏性越来越明显;细观分析显示随着加载速率的减小,拉裂纹和剪裂纹均增多,破坏模式由拉伸破坏向拉伸、剪切联合破坏的复合破坏转化;应用离散单元软件自编Fish语言,通过实时更新细观参数可实现压密阶段,宏观黏性性质主要由细观黏壶参数法向临界阻尼比和切向临界阻尼比影响。研究加载速率对储层砂岩宏细观力学性质的影响,可为地下储气库安全生产开采提供借鉴。

To study the effects of loading rate on macroscopic and mesoscopic mechanical properties of sandstone,a three-dimensional particle flow model(PFC3 D)that was based on parallel bond model and linear contact model with viscous damping was established,and a sandstone viscous discrete element analysis method was put forward.Mesoscopic parameters calibrations were done by control variable method and trial-and-error method.Compression test simulations with different loading rates were worked with the particle flow model through the selfmade fish language.The study suggests that the peak strength,elastic modulus,Poisson’s ratio and internal friction angle of sandstone all decrease,and the axial viscoplastic strain and the viscosity become more obvious when the loading rate decreases.The mesoscopic analysis shows that with loading rate decrease,both tensile crack and shear crack increase and the failure mode changes from tensile failure to combined failure of tension and shear.Using the fish language from the discrete element software PFC(Particle Flow Code),the compaction stage can be realized by updating the mesoscopic parameters in real time.Macroscopic parameters of the model are significantly affected by microscopic parameters,and the macroscopic viscosity is mainly affected by normal critical damping ratio and tangential critical damping ratio of mesoscopic viscosity parameters.The study on the effect of loading rate on the macroscopic and mesoscopic mechanical properties of reservoir sandstone can provide reference for safe production and mining of underground gas storage.