粒料材料颗粒破碎导致的颗粒形态和回弹模量演变机理研究

Unbound granular materials (UGM) have been widely used as pavement base/subbase and railroad ballast because of their high shear resistance, high permeability and low permanent deformation characteristics. Particle breakage of UGM can lead to significant changes of materials’ skeleton, gradation and morphological features, which can adversely affect their engineering properties including mechanical properties, permeability, and freeze-thaw durability. The biggest change of current research on the related topic is how to accurately quantify particle morphology and resilient modulus evolutions of UGM under simulated compaction and traffic loading conditions. Therefore, the proposed study aims at exploring the scientific reasons of the “particle breakage” and “resilient modulus reduction” of UGM under dynamic compaction and traffic loads based on the quantitative analysis of evolution of particle macroscopic and microscopic morphological features. In this study, I propose to develop a new 3D image analysis algorithm to accurately segment image with a large number of particles in contact with each other and quickly calculate the micro and macro morphological features of each particle. In addition, based on the field-measured traffic loading data and previous research results, I propose to improve the laboratory resilient modulus testing method and equipment, and conduct both the improved resilient modulus and the laboratory Aggregate Abrasion and Image Analysis (GAIA) test, which is developed by the applicant to evaluate the breakage and abrasion characteristics of UGM under simulated field compaction loads, to comprehensively study the rule of different UGM’s gradation, particle morphology, and resilient modulus evolutions under dynamic compaction and traffic loading conditions.

粒料类材料具有抗剪强度高、透水性强、永久变形小的工程特性，被大量用于修筑公路和铁路基层。累积脉冲荷载能够导致粒料材料颗粒破碎，改变其骨架结构、颗粒形态、耐久性，从而导致材料回弹模量降低、永久变形增大。现阶段相关科学研究面临的主要问题是难以真正定量分析粒料材料在压实和车辆脉冲载荷下的颗粒宏细观形态和力学性能演变规律。因此，申请人拟通过定量分析颗粒宏细观形态变化探索粒料材料在压实和车辆脉冲荷载下的“颗粒破碎规律”和“回弹模量演变规律”两个关键科学问题。通过研发大量颗粒在相互接触情况下的3D图像重构和几何形态算法，并基于申请人之前研究成果对室内回弹模量室内试验方法及设备进行优化改进，结合申请人提出的用于测试粒料材料在不同压实荷载下磨耗和破碎特性的GAIA试验方法，对常用粒料材料在不同压实和车辆脉冲载荷下的材料级配、颗粒宏细观形态以及力学性能演变机理开展系统研究。

本项目针对路面基层粒料由于施工压实和车辆荷载导致的颗粒形态和力学性能演变规律的关键科学问题开展研究。本研究基于Watershed（分水岭）图像分析算法研发了的大量相互接触颗粒图像接触点快速识别和分割算法和颗粒粒径、球度、棱角度参数的计算几何图像分析算法，为快速定量化分析粒料试件级配和粒形参数分布范围提供了快速、简单且准确的测试技术；基于该技术，提出了考虑粒料级配、球度和棱角度在室内试验前后变化情况的粒料破碎评估参数；针对粒料室内回弹模量试验方法，定量分析了试验规程和设备参数对试验结果重复性的影响，为探索粒料回弹模量影响因素和变化规律提供了更加准确的试验方法；基于前述研究成果，本研究将图像分析技术与传统室内压实和回弹模量试验方法相融合，探索了粒料在施工压实和车辆荷载作用下的颗粒形态和力学性能影响因素和规律。研究结果显示：（1）所研发的粒料图像采集设备和级配分析方法能够快速（约10分钟）确定粒料级配，试验结果准确（误差-2~4%），且受人为因素影响小，满足相关规范要求；（2）验证了所研发的基于图像分析的颗粒球度和棱角度参数的准确性，并提出了考虑颗粒宏细观形态分布情况的粒料破碎评估方法及参数；（3）针对粒料回弹模量试验方法，研究发现回弹模量试验设备导致的结果可重复性误差为0.8~5.6MPa，使用内置式LVDT代替外置式LVDT作为粒料室内回弹模量试验的应变测量手段可行且更为真实；路面基层粒料回弹模量试验规程要求的0.1s加载时长过短，无法模拟真实车速和车辆荷载，导致测试结果偏高；（4）基于大量室内试验结果分析，粒料在振动压实荷载作用下会产生粒径和形态变化，但单个颗粒的变化将具有很大的不确定性，材料粗颗粒含量和含水率越低，破碎磨损越明显；室内回弹模量试验导致的试件颗粒破碎远小于振动压实试验；粒料级配对回弹模量有着显著的影响，但其影响效果远小于应力水平；NCHRP 1-28A预测模型对粒料回弹模量预测效果最好，且拟合度随试件中粗集料含量的增大而增加。