粒间摩擦对岩土颗粒材料三维力学行为的影响机制

Mechanism of inter-particle friction effect on 3D mechanical response of granular materials

颗粒间摩擦是影响岩土颗粒材料力学特性的重要因素之一,现有研究主要集中在粒间摩擦对颗粒集合体堆积、宏观剪切强度等的影响,而其在复杂应力路径下对岩土颗粒材料的影响机制尚不明确。采用离散单元法(DEM)进行了颗粒材料的真三轴加载路径数值试验,通过改变颗粒间摩擦系数μ来研究粒间摩擦对颗粒材料宏观力学特性的影响。对比了4种三维强度准则,发现当0.2<μ≤0.5时,Lade-Duncan和Matsuoka-Nakai准则能较好地拟合不同加载路径下的数据点。采用平均接触力将颗粒体系的接触网络划分为强、弱两个子网络,分析了强、弱接触网络的配位数分布、接触力和组构各向异性等。结果表明在峰值剪应力状态,随着颗粒间滑动摩擦系数μ的增加,强接触网络中参与形成"力链"的颗粒数目基本不变,但强接触网络中颗粒间法向接触力明显增加以及法向接触力各向异性加强,这是导致宏观抗剪强度增大的主要原因。而弱接触网络的配位数分布随μ值明显变化,其对颗粒体系剪胀程度的增加贡献显著。

The inter-particle friction is regarded as an important factor that affects the stress and deformation characteristics of granular materials.The existing researches mainly focus on the influences of inter-particle friction on the accumulation characteristics and the macro shear strength,but the mechanism of its influences on the granular materials under the complex stress path has not yet been clarified.A series of true triaxial tests on granular materials are carried out by using the discrete element method(DEM),and the friction coefficientμis changed to reflect the effects of inter-particle friction on the macro-mechanical properties.The prediction capability of four three-dimensional strength criteria under different inter-particle frictions is discussed,and it is found that the Lade-Duncan and Matsuoka-Nakai criteria have better prediction capability when 0.2<μ≤0.5.In addition,the stress tensors,the distribution of coordination numbers and the fabric tensors of strong and weak contact networks(divided by average contact force)are also studied.The results show that with the increase of inter-particle frictionμ,the number of particles forming"force chains"in the strong contact network is basically unchanged,but the normal contact force and normal contact force anisotropy in the strong contact network increases significantly,which mainly causes the enhancement of the macro shear strength.The distribution of coordination numbers of the weak contact network changes greatly with the value ofμ,which contributes significantly to the increase of the dilatancy of the particle system.