Woodman James, Ougier-Simonin Audrey, Stavrou Anastasios, Vazaios Ioannis, Murphy William, Thomas Mark E, Reeves Helen J
University of Leeds, School of Earth & Environment, West Yorkshire, UK.
Present Address: Jacobs Engineering Group Inc., 1 City Walk, Leeds, UK.
Geotech Geol Eng (Dordr). 2021;39(7):4795-4815. doi: 10.1007/s10706-021-01794-z. Epub 2021 Apr 1.
Thermo-mechanical loading can occur in numerous engineering geological environments, from both natural and anthropogenic sources. Different minerals and micro-defects in rock cause heterogeneity at a grain scale, affecting the mechanical and thermal properties of the material. Changes in strength and stiffness can occur from exposure to elevated temperatures, with the accumulation of localised stresses resulting in thermally induced micro-cracking within the rock. In this study we investigated thermal micro-cracking at a grain scale through both laboratory experiments and their numerical simulations. We performed laboratory triaxial experiments on specimens of fine-grained sandstone at a confining pressure of 5 MPa and room temperature (20 ), as well as heating to 50 , 75 and 100 prior to mechanical loading. The laboratory experiments were then replicated using discrete element method simulations. The geometry and granular structure of the sandstone was replicated using a Voronoi tessellation scheme to produce a grain based model. Strength and stiffness properties of the Voronoi contacts were calibrated to the laboratory specimens. Grain scale thermal properties were applied to the grain based models according to mineral percentages obtained from quantitative X-ray diffraction analysis on laboratory specimens. Thermo-mechanically coupled modelling was then undertaken to reproduce the thermal loading rates used in the laboratory, before applying a mechanical load in the models until failure. Laboratory results show a reduction of up to 15% peak strength with increasing thermal loading between room temperature and 100 , and micro-structural analysis shows the development of thermally induced micro-cracking in laboratory specimens. The mechanical numerical simulations calibrate well with the laboratory results, and introducing coupled thermal loading to the simulations shows the development of localised stresses within the models, leading to the formation of thermally induced micro-cracks and strength reduction upon mechanical loading.
热机械载荷可能出现在众多工程地质环境中，其来源既有自然的，也有人为的。岩石中不同的矿物和微缺陷会在晶粒尺度上导致非均质性，从而影响材料的力学和热学性能。暴露在高温下会导致强度和刚度发生变化，局部应力的积累会在岩石内部产生热致微裂纹。在本研究中，我们通过实验室实验及其数值模拟，在晶粒尺度上研究了热致微裂纹。我们在围压为5MPa、室温（20℃）下，以及在机械加载前加热至50℃、75℃和100℃的条件下，对细粒砂岩试样进行了实验室三轴实验。然后使用离散元方法模拟复制了实验室实验。使用Voronoi镶嵌方案复制砂岩的几何形状和颗粒结构，以生成基于颗粒的模型。将Voronoi接触的强度和刚度特性校准到实验室试样。根据对实验室试样进行定量X射线衍射分析获得的矿物百分比，将晶粒尺度的热学特性应用于基于颗粒的模型。然后进行热机械耦合建模，以再现实验室中使用的热加载速率，然后在模型中施加机械载荷直至破坏。实验室结果表明，随着室温至100℃之间热加载的增加，峰值强度降低了高达15%，微观结构分析表明实验室试样中出现了热致微裂纹。力学数值模拟与实验室结果校准良好，在模拟中引入耦合热加载表明模型内部出现了局部应力，导致热致微裂纹的形成以及机械加载时强度降低。
