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Discrete element modelling of clay

粘土的离散元建模

基本信息

批准号：
EP/S016228/1
负责人：
Glenn McDowell
金额：
$ 64.74万
依托单位：
University of Nottingham
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2019
资助国家：
英国
起止时间：
2019 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FS016228%2F1
关键词：
Discrete element modelling clay

项目摘要

The aim of this project is to use the Discrete Element Method to explain the particle-scale origins of the mechanical behaviour of clay. Clays, like all soils, are granular materials composed of solid particles and fluids. Yet clays exhibit the most complex behaviour and remain the least understood. The Critical State Soil Mechanics framework has been used to describe and predict the general behaviour of soils for around 60 years, but the origins of this behaviour have rarely been investigated. Within this guiding framework, all soils (i.e. both sands and clays) exhibit the same general patterns of behaviour. For example, when a soil is sheared, it will dilate or contract, depending on the stress level and how dense or loose the initial soil is. If a soil is compressed under increasing isotropic stress, after a high enough stress is reached, a permanent decrease in volume occurs. For sands, this is known to be due to particle crushing. In fact, the normal compression line, which is a line in volume-stress space, which a sample of soil follows when subject to compression, has been shown recently by McDowell and de Bono (2013) to be solely a function of the particle strengths (specifically, the rate at which the average particle crushing strength increases with decreasing particle size). This therefore provides a micro mechanical explanation for a well-known and fundamental feature of soil behaviour.For clays on the other hand, the underlying mechanisms which control the bulk behaviour remain unknown. This is due to difficulty in observing or measuring particle interactions due to their small size. The individual particles in clays are too small to be seen with the naked eye, and are so small that the interactions between these particles are controlled by molecular forces rather than mechanical forces. Clay particles also have more complicated shapes when compared with sand, such as hexagonal platelets or cylindrical tubes. The inter-particle forces acting between clay particles are highly dependent on the environmental conditions (e.g. pH, salinity, etc.). These forces can be attractive or repulsive, and different forces may exist between the different parts of clay particles (e.g. the 'edges' and 'faces'). The variety of different combinations of forces between particles leads to many different geometrical arrangements of particles in real clays. Just how the particles interact during engineering applications (i.e. loading/unloading) and how their geometrical arrangement changes or controls the macroscopic behaviour remain speculative, and the particles are presently impossible to observe experimentally due to the small size.There is therefore no fundamental understanding as to what causes or leads to observed phenomena such as a decrease in volume when subjected to increasing (e.g. isotropic) stress, or volume change during shearing. These phenomena will be explained by using the Discrete Element Method (DEM) to model and investigate the behaviour of clays with varying inter-particle forces. DEM is a numerical tool which computes the interactions and motion of a large number of discrete particles. By default, the majority of DEM simulations are typically only concerned with mechanical contacts between entities, which are easily calculated; yet it is possible to implement any number of custom, more complex interaction laws. DEM simulations have been typically limited by the computational hardware available, and to date clay has rarely been modelled. This ambitious project will use DEM to 'look inside' a numerical clay sample with a large number of particles and realistic particle interactions as it undergoes a variety of stress path tests, changing the way we understand (and teach) clay behaviour.Revealing the underlying origins of clay behaviour will allow engineers and researchers to develop more accurate models and ultimately will lead to safer, more economic designs of foundations and underground structures.

这个项目的目的是使用离散单元法来解释粘土力学行为的颗粒尺度起源。粘土和所有土壤一样，是由固体颗粒和流体组成的颗粒状物质。然而，粘土表现出最复杂的行为，仍然是最不了解的。近60年来，临界状态土力学框架一直被用来描述和预测土壤的一般行为，但这种行为的起源却很少被研究。在这一指导框架内，所有土壤（即砂和粘土）表现出相同的一般行为模式。例如，当土壤被剪切时，它会膨胀或收缩，这取决于应力水平和初始土壤的密度或松散程度。如果土壤在增加的各向同性应力下被压缩，在达到足够高的应力之后，体积发生永久性减小。对于砂，已知这是由于颗粒破碎。实际上，法向压缩线是体积应力空间中的一条线，土样在受到压缩时遵循该线，最近McDowell和de Bono（2013）已经表明，法向压缩线仅是颗粒强度的函数（具体而言，平均颗粒压碎强度随颗粒尺寸减小而增加的速率）。这为土壤行为的一个众所周知的基本特征提供了一个微观力学解释。另一方面，对于粘土，控制整体行为的潜在机制仍然未知。这是由于难以观察或测量粒子的相互作用，因为它们的尺寸很小。粘土中的单个颗粒太小，肉眼无法看到，并且这些颗粒之间的相互作用是由分子力而不是机械力控制的。与沙子相比，粘土颗粒也具有更复杂的形状，例如六边形片状物或圆柱形管。作用于粘土颗粒之间的颗粒间力高度依赖于环境条件（例如pH、盐度等）。这些力可以是吸引力或排斥力，并且在粘土颗粒的不同部分（例如“边缘”和“面”）之间可以存在不同的力。颗粒间力的不同组合导致了真实的粘土中颗粒的许多不同的几何排列。在工程应用中粒子是如何相互作用的（即加载/卸载）以及它们的几何布置如何改变或控制宏观行为仍然是推测性的，由于颗粒尺寸小，目前不可能通过实验观察到。因此，对于什么原因或导致观察到的现象，例如当受到增加的压力时体积减小，没有基本的理解。（例如，各向同性）应力或剪切期间的体积变化。这些现象将解释通过使用离散元法（DEM）建模和调查的粘土与不同的颗粒间的力的行为。DEM是一种数值工具，它计算大量离散颗粒的相互作用和运动。默认情况下，大多数DEM模拟通常只关注实体之间的机械接触，这很容易计算;但可以实现任何数量的自定义，更复杂的相互作用定律。DEM模拟通常受到可用计算硬件的限制，迄今为止，粘土很少被建模。这个雄心勃勃的项目将使用DEM来“查看”具有大量颗粒和真实颗粒相互作用的数字粘土样本，因为它经历了各种应力路径测试，改变了我们的理解方式揭示粘土行为的潜在起源将使工程师和研究人员能够开发更准确的模型，并最终导致更安全，更经济的基础和地下结构设计。