颗粒状岩土材料在临界状态下的剪切机理与抗剪强度研究

Granular soil, as a typical kind of discrete media, exhibits rather complex shear and dilatancy behaviors. Nevertheless, conventional studies which are founded upon continuum mechanics theories have led to misunderstandings among researchers, in respect of the special dilatancy state－critical state and its related theories. In particular, there remain some evident divergences in understanding the essential shearing mechanism and shear strength at critical state for granular soil. By focusing on the discrete nature of granular soil, this research project presents an investigation into the effect of basic particle attributes which primarily refer to particle size, particle shape, inter-particle friction, etc., on the mechanical behavior and shear strength of granular soil at critical state. The main research works include: (1) the experimental study on the effect of basic particle properties on the macroscopic shear behavior and shear strength at critical state; (2) the numerical examination from a microscopic perspective into the influence mechanism of basic particle attributes on the microstructures and microscopic particle motions at critical state; (3) the establishment of a micromechanical model of critical state and the derivation of a mathematical expression of critical state shear strength. These investigations are aimed at: (a) exploring the fundamental shearing mechanism at critical state for granular soil, (b) clarifying the physical meaning of critical state shear strength, (c) providing precious experimental and theoretical evidences for the enrichment and improvement of the current critical state theories as well as shear strength theories, and (d) building up a solid foundation for the formulation of macroscopic constitutive model at a microscopic level.

颗粒状岩土材料作为一种典型的离散介质，其剪胀行为相当复杂。基于连续介质力学的传统研究使学者们对其特殊剪胀状态－临界状态及其相关理论产生了不同的理解，尤其对颗粒状岩土材料在临界状态的剪切机理与抗剪强度的认识还存在明显的分歧。本项目拟针对颗粒状岩土材料的离散性，研究颗粒基本性质，如颗粒大小、形状、颗粒间摩擦等，对其在临界状态下的力学行为和抗剪强度的影响，主要研究包括：（1）通过试验研究颗粒基本性质对临界状态下的宏观剪切行为和抗剪强度的影响；（2）通过数值模拟从细观上分析颗粒基本性质对临界状态下细观结构和颗粒细观运动的影响规律；（3）建立临界状态细观力学模型并推导临界状态抗剪强度表达式。本项目旨在通过这些研究来从根本上揭示颗粒状岩土材料在临界状态的剪切机理，阐明临界状态抗剪强度的物理意义，为丰富和完善土的临界状态理论与抗剪强度理论提供重要的试验与理论支持，为土的宏观本构模型微观化奠定坚实的基础。

颗粒岩土材料由于其离散性，整体的力学行为十分复杂。学者们虽然通过大量的试验、理论和数值方法来研究颗粒岩土材料的力学行为和特征，并得到了较为全面的认识，但对其在临界状态的剪切行为和抗剪强度的认识仍存在一定的分歧。本项目紧紧围绕颗粒岩土材料的离散性这一本质属性，通过试验、数值和理论的方法来研究颗粒基本性质和组构特征对其整体力学行为，尤其对其在临界状态的剪切行为和抗剪强度的影响，获得了一系列的研究成果和发现：（1）通过直剪试验发现颗粒基本性质如摩擦和大小，显著影响颗粒材料的剪胀和临界状态剪切行为，并提出了考虑颗粒基本性质影响的剪胀关系式，阐明了颗粒基本性质对临界状态摩擦角的影响机理；（2）通过数值模拟研究发现细颗粒能引起颗粒岩土材料的反常剪切行为，其宏观的剪胀和剪缩行为都与细颗粒在土骨架中的分布形态和运动紧密相关，揭示了颗粒级配特征对临界状态下细观结构和颗粒细观运动的影响规律；（3）颗粒岩土材料在不排水状态下的宏观剪胀行为以及在临界状态下的剪切行为和细观力学响应不受初始结构各向异性的影响，论证了宏观尺度上临界状态线的唯一性；（4）提出了考虑土体离散特性的临界状态细观力学理论模型，通过数学推导建立了反映细观剪切机理的临界状态抗剪强度的理论表达式，揭示了临界状态抗剪强度的物理意义。这些研究成果为丰富和完善土的临界状态理论与抗剪强度理论提供了重要的试验与理论支持，为土的宏观本构模型微观化奠定了坚实的基础。