基于离散元模拟和透明土模型试验的圆柱快速贯入颗粒材料过程动力分析

The engineering applications of rapid penetration into granular materials, e.g., pile driving, dynamic penetration testing, projectile impact, can be simplified as the dynamic problem of rapid penetration of cylinders into granular materials. The shape and breakage of granular particles under impact loading greatly influences the dynamic response, granular flow, energy dissipation, penetration depth, cavity formation during the object’s rapid penetration into granular media. Therefore, to describe the shape of sand particle and breakage under dynamic loading, this project is first to create the irregular and crushable discrete element by bonding spherical particles together, meanwhile establishing the failure criterion of bond between particles. Based on this model, discrete element simulations are performed on the rapid penetration of cylinders into granular media to investigate the micromechanical response of granular particles in this dynamic event. Further to develop the laser speckle image measurement technique in transparent soil model, conduct experiments on the rapid penetration of cylinders into transparent soil, and accomplish the 3D visualization of this process and mesoscale measurement of particles’ movement and deformation. Then to discuss the influences and mechanisms of the micro, meso parameters and particle breakage on the rapid penetration event. This project is to conduct discrete element simulation and transparent soil model experiments on the cylinders’ rapid penetration into granular media, which helps to reveal the micromechanical evolution of this dynamic process and provide scientific basis for the related engineering applications。

颗粒材料中快速贯入的工程应用如打桩、动力贯入试验、弹体冲击等可简化为圆柱快速贯入颗粒材料的动力问题。颗粒的几何形态和冲击破碎特性对贯入过程的动力响应、颗粒流动、能量耗散和传播、贯入深度、孔洞形成等有重要影响。为此，本项目针对砂土颗粒的几何形态和冲击荷载下的破碎特性，粘结组合颗粒单元构造考虑应变率效应的非规则、可破碎的颗粒单元模型，并建立粘接颗粒间的破坏准则；基于这一模型进行离散元模拟，研究颗粒介质在圆柱快速贯入过程中的细观力学响应；发展透明土中激光散斑成像测量方法，进行圆柱快速贯入透明土的模型试验，实现圆柱快速贯入的三维可视化及颗粒运动和变形的介观尺度测量；探讨颗粒材料的细观、介观结构参数和颗粒破碎对圆柱快速贯入过程的影响机理。本项目通过对圆柱快速贯入颗粒材料开展离散元模拟和透明土模型试验研究，有助于揭示这一动力过程的细观力学演变规律，为颗粒材料中物体快速贯入相关的工程应用提供科学依据。

颗粒材料中快速贯入的工程应用如打桩、动力贯入试验、弹体冲击等可简化为圆柱快速贯入颗粒材料的动力问题。为此，本项目针对砂土颗粒中圆柱体快速贯入的问题开展了一系列的研究工作。采用室内模型试验试验研究了不同长宽比，不同头部形状的圆柱时间快速贯入颗粒材料的动力过程，建立了圆柱试件快速贯入颗粒材料的基于能量的动力方程，开发了磁性构建基于电磁原理的加速下落试验装置，开发了透明土模型试验中三维图像测量的层析装置和重构方法。采用DEM 数值方法模拟了桩基础贯入的过程并提出了不同粒径分区的建模方法，加快了计算的速度。另外研究了颗粒冲击荷载下的破碎分形规律，构建了考虑应变率和颗粒破碎的本构模型。本项目的研究结果，可以帮助人们进一步更好的认识物体动力贯入颗粒材料过程和规律，并为实际工程应用如打桩分析，海洋工程中的动力锚的安装分析等提供科学的依据，具有重要的工程应用价值和科学意义。