旋转与挤压荷载作用下散粒介质宏细观力学机理研究

Based on the previous research,present study plans to reveal the mechanical mechanism of granular medium under the complex loading of rotation and extrusion from the macro-meso scale by means of the self-developed visualization interface test, as well as laboratory model tests and 3D discrete-continuum coupling numerical simulation. The main study contents include as follows.(1)The meso-mechanics mechanism of nonlinear contact characteristics between granular and structure under the coupling condition of shearing and compressing is revealed by analysis of interface meso-fabric evolution. The meso damage interface model is established based on visual contact test by revealing the meso mechanism of nonlinear interaction mechanics characteristics.(2) The model tests verify the meso damage interface model and reveal granular meso-fabric evolution and macro mechanical characteristics during the loading process of rotary-extrusion in the scale physical condition.(3)The discrete-continuum coupled analysis module of considering interface micromechanics contact characteristics is established by implanting the meso damage interface model into the program.The cylinder expanding problem under loading of rotary-extrusion is simulated at full size. The macro and micro mechanics characteristics of granular under loading of rotation with the extrusion from mesoscopic level is revealed by verification of numerical analysis and model test. This study can provide micromechanics basis for soil and structure interaction mechanism research under complex loading conditions, but also theoretical basis for the evaluation of the deep foundation bearing capacity.

本申请项目在前期研究基础上，利用可视化接触试验、室内模型试验和离散-连续耦合数值模拟，从宏细观双尺度揭示散粒介质在旋转与挤压复杂荷载作用下力学机制。主要研究包括：（1）分析接触面颗粒在切向滑移与径向挤压耦合接触作用过程中颗粒细观组构演化，揭示接触作用的非线性力学特征的细观机理，建立界面细观损伤接触模型；（2）通过模型试验，验证所建立的细观接触模型的正确性，揭示缩尺物理状态下旋转与挤压加载过程散粒体的细观组构演化规律和宏观力学特性；（3）将细观接触模型植入离散－连续耦合程序，建立复杂荷载作用下考虑界面细观接触特性的离散－连续耦合分析模块，进行实际尺度旋转与挤压加载形式的挤土扩孔问题模拟，通过与模型试验验证，从细观层面揭示数值实际尺度状态下旋转与挤压荷载作用下散粒体的宏细观力学机理。本研究可为复杂加载条件下土与结构物相互作用机制的深入研究提供细观力学基础，还可为深基础承载力评价提供理论依据。

本项目采用纳米压痕、单颗粒接触试验、复杂应力条件接触试验、模型试验和离散元数值模拟从微观到宏观研究散粒介质在旋转与挤压复杂荷载作用下力学响应，揭示了散粒介质多尺度力学作用机理。取得的主要研究成果有：（1）发现了石英砂纳微观硬度规律，揭示了不同尺度粒径的石英砂破碎机制，粗粒破碎兼有解理断裂和贝壳状断裂，细粒主要为解理断裂；（2）单颗砂颗粒接触为非线性接触弹性段和非线性接触塑性段，弹性接触段符合Hertz弹性接触模型，屈服点受接触点两物体屈服应力较小者控制；（3）建立了散粒体最小孔隙比的计算模型，揭示了不同细粒含量的微观结构演化机制，细粒含量40%左右时，密实度最大，颗粒结构最稳定；（4）揭示了复杂应力条件的散粒体宏观接触力学特性；（5）开发了两种离散元大尺度建模方法，环向周期边界法和变粒径法；（6）揭示了螺旋挤扩钻具旋转与挤扩成孔机制，存在过度旋转和旋转不足两种成孔机制；（7）螺旋挤扩钻具挤扩对散体土体宏观产生孔隙比变化，细观上造成接触组构变化，这将影响土体的力学特性。本项研究为散粒介质力学特性研究提供了新方法，取得的研究成果有助于形成散粒介质体系多尺度研究体系。