The contact mechanics of sand and rock grains

砂石颗粒的接触力学在需要离散而非连续方法的土木或石油工程问题中至关重要，例如泥石流，油井行为，但颗粒土力学的最新技术在于颗粒的实验（x射线CT）和数值（离散元- dem）研究，其中通常假设简单，光滑的形状和简单的接触规律。很可能在很长一段时间内，随着计算机能力的提高，所有岩土工程模型都将是离散的。主管目前对压舱物的拨款旨在为DEM重建现实粒子，但为粒子间接触制定本构律将需要另一个纯粹基本的项目。地质成因颗粒表面凹凸不平（0.1 ~ 10 m），形状复杂。唯一可用的接触模型是在20世纪70年代为工程表面、正常载荷和许多接触模型导出的。在现有的粗糙表面模型中，要么假设凹凸不平的变形是弹性的，要么是塑性的，或者两者兼而有之，没有共识，但两者都不适用于土壤/岩石颗粒。人们需要退后一步，以便能够为土/岩石颗粒之间的接触产生适当的本构律。这需要设计颗粒对颗粒的测试，以研究接触行为的特定方面，表征接触表面，并从弹性和塑性理论发展本构定律，但由这些结果提供信息。Baudet基于先进的分形理论，提出了一种量化颗粒表面粗糙度及其随载荷变化的新方法。她打算与Murthy博士合作，Murthy博士是著名的印度科学研究所的摩擦学家/土壤力学家，伦敦大学学院全球参与办公室鼓励与该研究所合作。她和穆尔蒂通过皇家学会和双印度奖学金计划建立了牢固的联系。UCL土壤实验室拥有独特的颗粒间测试设备，由Coop建造（图1），能够控制和分辨载荷（1-1,000N，分辨率为0.01N）和位移（0-5mm，分辨率为0.02m），用于正常和切向载荷，以及先进的光学剖面仪，用于粗糙度测量。

The contact mechanics of sand and rock grains can be critical in civil or petroleum engineering problems that require a discrete not continuum approach e.g. debris flow, oil well behaviour, but the state-of-the-art in particulate soil mechanics lies in experimental (x-ray CT) and numerical (discrete element-DEM) studies of grains where simple, smooth shapes and simplistic contact laws are often assumed. It is probable that in the very long term, as computer power increases, all geotechnical modelling will be discrete. The supervisors' current grant on ballast aims at recreating realistic particles for DEM, but developing constitutive laws for the inter-particle contact would require another, purely fundamental, project. Grains of geological origin have surface asperities (0.1-10 m) and complex shapes. The only contact models available were derived for engineered surfaces, for normal loading and many in the 1970s. In available models for rough surfaces, it is either assumed that asperities deform elastically, or plastically, or both, without consensus, but neither works well for soil/rock grains. One needs to take a step back to be able to generate the appropriate constitutive laws for contact between soil/rock grains. This requires designing particle-to-particle tests to investigate specific aspects of contact behaviour, characterising the contact surfaces and developing constitutive laws from elastic and plastic theory but informed by these results. Baudet has developed a novel method to quantify grain surface roughness and its evolution with loading based on advanced fractal theory. She intends to involve Dr Murthy, tribologist/soil mechanics from the prestigious Indian Institute Science with which collaboration is encouraged by UCL Global Engagement office. She and Murthy have established strong links through Royal Society and DUO-India Fellowship schemes. UCL soil laboratory possesses a unique apparatus for inter-particle testing, built by Coop (fig.1), able to control and resolve loads (1-1,000N with 0.01N resolution) and displacements (0-5mm with 0.02m resolution) for normal and tangential loading, and an advanced optical profilometer for roughness measurements.