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临界状态通常作为砂土等颗粒材料本构模型中的一种参考状态,是经典土力学框架的一个重要组成部分。根据砂土的细观结构特性,一些学者提出了描述砂土内部结构特性的状态参量,建立了状态相关的剪胀模型。然而受试验条件的限制,目前多采用常规三轴试验研究颗粒材料的临界状态和剪胀特性,未考虑中主应力因素。已有研究表明加载路径对颗粒材料的力学特性有一定影响,本文采用离散单元法模拟了颗粒材料真三轴应力路径试验,分析了加载过程中颗粒材料的应力应变特性及中主应力对临界状态的影响。结果表明:颗粒材料的临界状态线(CSL)在e-lg p平面内是唯一的,与中主应力系数无关。临界状态应力比与应力罗德角的关系可以采用角隅函数近似表达。基于状态相关的剪胀理论,采用Lode角的函数(角隅函数)表示模型参数,提出一个新的应力-剪胀模型。数值试验结果表明,本文采用的三维剪胀模型能够较好地反映了离散元数值模拟中颗粒材料在三维应力路径下的剪胀特性,然而公式的适用性需要更多的试验验证和理论研究。
Critical state is usually used as a reference state in the constitutive model of sand and other granular materials and is an important part of classical soil mechanics framework. According to the mesostructural characteristics of sand, some scholars have proposed the state parameters describing the internal structural characteristics of the sand, and established a state-dependent dilatancy model. However, due to the limitation of the experimental conditions, the critical state and dilatancy characteristics of the granular materials are mostly studied by the conventional triaxial tests. The main stress factors are not considered. Previous studies have shown that the loading path has some influence on the mechanical properties of granular materials. In this paper, the true triaxial stress paths of granular materials were simulated by discrete element method. The stress-strain characteristics of the granular materials and the influence of the principal stress on the critical state Impact. The results show that the critical state line (CSL) of the granular material is unique in the e-lgp plane, independent of the principal stress coefficient. The relationship between critical state stress ratio and stress Rhode angle can be approximated by corner function. Based on the state-dependent dilatancy theory, a new stress-dilatancy model is proposed using the Lode angle function (corner function) as a model parameter. The numerical results show that the three-dimensional dilatancy model used in this paper can well reflect the dilatancy behavior of granular materials under three-dimensional stress path in discrete-element numerical simulation. However, the applicability of the formulas requires more experimental verification and theoretical research.