主应力轴旋转下尾砂"强非共轴性"的宏细观力学机制与本构描述

The influence of particle shape and internal structure on the mechanical behavior of tailing sands is very significant. In classical soil mechanics theory, the influence of the meso-structure on non-coaxiality of tailing sands under principal stress rotation cannot be studied, which is the major problem restricting the reliability of safety evaluation of tailings structures. In this project, preliminary tests on tailing sands under principal stress rotation have been done and the scientific phenomenon-strong non-coaxiality appeared as expected. Based on this phenomenon, by breaking through limitation of the traditional equivalent continuum and coaxial theories, a hypothesis that there is a function correlation between the meso-structure parameters and the non-coaxial angle of tailings is proposed. High performance particle imaging analysis, hollow cylindrical torsion shear apparatus tests and three-dimensional discrete element simulations will be used to study the strength and non-coaxial deformation characteristics, the evolution of particle contact, arrangement, spatial distribution, and the contact force of tailing sands with various particle morphologies, and the gradations and densities under the rotation of principal stress axis. In order to verify the hypothesis of function correlation, find out the main controlling factors of non-coaxial angle and reveal macro-meso mechanics of strong non-coaxiality of tailing sands, a new homogenization method for non-convex granular material will be developed to study the meso-structure of tailing sands, and the multi-scale correlation between the micro properties and the macro non-coaxiality will be established. Eventually, a novel non-coaxial elastoplastic constitutive model of macro-meso-incorporation of tailing sands will be establishe. This study will be helpful to improve the safety assessment and disaster prediction of tailings structures, and providing a new theory and method for the decision-making of disaster prevention and mitigation.

尾砂极具特殊性的颗粒形貌与细观结构对其宏观力学行为，尤其是主应力轴旋转下的非共轴变形特性影响巨大，经典土力学理论无法对此进行量化描述，是制约尾矿构筑物安全评价可靠性的关键瓶颈。项目从预试验中发现的尾砂“强非共轴性”特征科学现象出发，突破传统连续介质和共轴理论的局限，提出尾砂细观结构参量与宏观非共轴角存在函数相关性的科学假说；利用高精度颗粒图像分析、空心圆柱扭剪试验及三维离散元模拟，研究不同颗粒形貌、级配和密实度的尾砂在主应力轴旋转下的强度与变形特性，解译颗粒接触、排布和粒间作用力等细观演化规律；通过发展符合尾砂细观特征的非凸颗粒散体结构均匀化方法，构建尾砂结构参量与非共轴角的多尺度关联，找出主控影响因素，验证并明确假说中的函数关系；最终揭示尾砂强非共轴性的力学机制，建立新的宏细观结合的尾砂非共轴弹塑性本构模型。本研究有助于提高尾矿构筑物安全评价和灾害预测水平，为防灾决策提供新理论和新方法。

（1）开展了尾矿砂定向剪切应力路径下的空心扭剪试验，探究了初始各向异性对尾矿砂强度及非共角变化规律的影响。研究表明：试样破坏时的强度随主应力方向角的增大先减小后增大，最小的破坏强度在α=75°时取得。非共轴角在加载初期最大（最大值小于15°），临近破坏时最小。综上所述，尾矿砂的破坏强度受各向异性影响显著且具有一定的非共轴变形特性。.（2）开展了尾矿砂主应力轴纯旋转的空心扭剪试验，探究了不同条件下，尾矿砂试样的非共轴变形特性。研究表明，试样内部孔隙率越大，试样的非共轴角平均值越小，非共轴角变化规律与偏应力水平及中主应力系数的相关性较小。随着主应力轴的旋转，非共轴角呈现出先减小后增大的规律，且最小值几乎都出现在旋转角为40°- 45°范围内。.（3）开展了尾矿砂联合荷载作用下的空心扭剪试验，探究了联合荷载作用下试样的非共轴变形规律。研究表明：主应力方向角与非共轴角呈反比关系，在试样临近破坏时非共轴角几乎为0。.（4）开展了聚丙烯纤维加筋尾矿砂的常规三轴试验，分别探讨了纤维掺量、初始相对密实度及有效围压对尾矿砂和加筋尾矿砂的强度、变形和颗粒破碎的影响规律。研究表明：相比素尾矿砂，加筋土的强度显著提高，最理想的纤维掺量应在0.3%左右。纤维形成的空间网状结构抑制了试样的变形。.（5）开展了聚丙烯纤维加筋尾矿砂不同应力路径下的空心扭剪试验，探究了掺入一定量的纤维后，不同应力路径下试样的强度及非共轴变形特性。研究表明：掺入纤维后，试样的破坏强度得到一定的提高。在纯主应力轴旋转应力路径下，纤维的掺入对非共轴角的影响最为显著。