Multi-scale testing and modeling particle size effects on primary and secondary compressibility of crushable granular materials

散粒体填料在土木工程中应用广泛，对其力学性能的了解至关重要。在应力-应变行为中的一个关键问题是颗粒破碎。简而言之，当颗粒间接触力超过颗粒强度时，一部分颗粒可能破碎，从而使粒度分布朝向更细和更多分散的材料改变。因此，对于给定的应力状态，可压缩性增加。此外，颗粒破碎是颗粒材料中的尺寸效应和蠕变应变的来源，这在工程和地质科学问题中可能是重要的，涉及高堆石坝、桩贯入、岩体不连续性中的颗粒填充、风化引起的岩石破碎、破碎岩石沉积物的沉降等。 基于破碎量与可压缩性之间的关系，根据宏观力学观测，通过拟合参数，建立了几种可破碎颗粒材料的唯象本构模型。然而，颗粒破碎的来源来自单个颗粒的断裂力学。换句话说，它取决于单个颗粒的几何和矿物学特征，通过颗粒接触的负载条件和环境条件。因此，为了开发基于物理的方法，多尺度方法似乎是合适的，但在这个问题上只进行了一些尝试，实验数据也非常缺乏。 在这项研究计划中，提出了一个全面的实验工作和理论的发展，以研究涉及的多尺度机制的颗粒尺寸对初级和次级可压缩性的可破碎颗粒材料的影响。该计划将允许通过微观，中观和宏观尺度进行广泛的分析。这项研究的实际应用将对岩土工程以及处理颗粒材料力学的其他学科产生极大的兴趣，例如陶瓷，制药，食品和采矿行业的粉末技术。

Granular fills are widely used in civil engineering and the understanding of their mechanical properties is essential. A key issue in the stress-strain behavior is particle breakage. Briefly, when intergranular contact forces exceed particle strength, a fraction of the particles could crush, changing the grain size distribution towards a finer and more polydisperse material. Consequently, the compressibility increases for a given stress state. Furthermore, particle breakage is the source of size effects and creep strains in granular materials, which could be significant in engineering and geoscientific problems, involving high rockfill dams, pile penetration, granular fills in discontinuities of rock masses, rock fragmentation by weathering, subsidence of fractured rock deposits, among others. Several phenomenological constitutive models for crushable granular materials have been developed according to macro-mechanical observations, based on relationships between the amount of breakage and the compressibility through fitted parameters. However, the source of grain crushing comes from the fracture mechanics of individual grains. In other words, it depends on geometrical and mineralogical characteristics of individual grains, on their loading conditions through particle contacts and on environmental conditions. Therefore, in order to develop physical-based methods, multi-scale approaches seem appropriate, but only a few attempts have been made on this subject and experimental data is quite scarce. In this research program, a comprehensive experimental work and theoretical developments are proposed in order to study the multi-scale mechanisms involved in particle size effects on primary and secondary compressibility of crushable granular materials. The program will allow a broad analysis through micro, meso and macro-scales. Practical applications of this research will be of great interest for geotechnical engineering, as well as other disciplines dealing with the mechanics of granular materials, such as powder technology in the ceramic, pharmaceutical, food and mining industries, for instance.