Exploring thermo-hydro-mechanical-chemical (THMC) coupled processes during swelling of clay-sulfate rocks

尽管岩石膨胀在岩土工程应用和地质过程中很重要，但人们对岩石膨胀的认识还不够充分，而它在工程项目规模上的影响是显著的。这项联合研究将汇集法国和德国合作伙伴的实验和建模技能，以表征、理解和模拟微观过程中岩石膨胀的宏观影响。计划中的研究将集中在粘土-硫酸盐岩石上，在那里粘土膨胀和化学膨胀一起发生，并相互影响。这项研究的首要目标是产生定量描述岩石热、水、力和化学(THMC)耦合膨胀行为的实验结果，并将结果转化为用于数值模拟的本构方程。研究计划分为四项任务。前三个任务是试验性的，将用于为任务4中开发的模型提供信息。任务1包括样本的准备和表征。将进行矿物学分析(X射线衍射法、Rietveld法、薄片分析)和化学分析(X射线荧光光谱分析)。在膨胀实验期间采集的流体样本也将被分析(微波等离子体原子发射光谱分析，滴定)。我们将在任务2中进行流动膨胀实验，以观察样品在膨胀过程中如何膨胀及其渗透性如何演变。为了理解和解释任务2中观察到的宏观膨胀行为，任务3将对样品进行较小规模的高级成像。我们将使用X射线计算机显微断层扫描(XRCT)和磁共振成像(MRI)直接观察孔结构和流体流动，以及它们在膨胀过程中的变化。此外，通过观察孔隙空间、密度和含水率的变化，可以在空间和时间上跟踪与膨胀同时发生的化学反应。这些实验还将得到扫描电子显微镜(SEM)、压汞孔隙度(MIP)和核磁共振低温疏松测量的补充。结果将使我们能够告诉我们流体流动(例如，岩石基质与结构面)和化学膨胀(转化的位置和时间)在哪里以及何时发生，以及它们与机械参数(例如密度/体积)和水力参数(例如孔隙度、流量)的关系。任务1到任务3中收集的数据将作为任务4中模型开发、校准和验证的基础。THMC本构关系将基于任务2和任务3中获得的数据推导，并通过快速傅立叶变换根据任务3中执行的微观结构观测进行预测。本构定律将在两个开源的THMC耦合有限元程序(BIL和OpenGeoSys)中实现，并在实验上进行验证。对这两种数值方法进行了比较。

Despite the importance in geotechnical applications and geological processes, the swelling of rocks is still insufficiently understood, while its effects at the scale of engineering projects are significant. This joint research will bring together the experimental and modeling skills of French and German partners to characterize, understand and model the macroscopic effects of rock swelling from microscale processes. The planned research will focus on clay-sulfate rocks, where clay swelling and chemical swelling occur together and influence each other. The overarching goal of the proposed research is to generate experimental results that quantitatively characterize the thermal, hydraulic, mechanical and chemical (THMC) coupled swelling behavior of rocks, and translate the results into constitutive equations for numerical simulations. The research plan is structured into four tasks. The first three tasks are experimental and will be used to inform the models developed in Task 4. Task 1 includes the preparation and characterization of the samples. Both mineralogical analysis (X-ray diffraction, Rietveld method, thin section analysis) and chemical analysis (X-ray fluorescence spectrometry) will be performed. Fluid samples taken during the swelling experiments will also be analyzed (microwave plasma atomic emission spectrometry, titration). We will perform flow-through swelling experiments in Task 2 to observe how samples swell and how their permeability evolves during swelling. To understand and interpret the macroscopic swelling behavior observed in Task 2, advanced imaging of the samples at a smaller scale will be performed in Task 3. We will use X-ray computed microtomography (XRCT) and magnetic resonance imaging (MRI) to make direct observations of pore structure and fluid flow, and their changes during swelling. Moreover, chemical reactions can be tracked in space and time contemporaneous with swelling by observing changes in pore space, density and water content. These experiments will be complemented by scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and NMR cryoporometry. The results will enable us to tell where and when both fluid flow (e.g., rock matrix versus discontinuities) and chemical swelling (location and time of conversion) occur, and how they are related to mechanical (e.g., density/volume) and hydraulic (e.g., porosity, flow rate) parameters. Data gathered in Tasks 1 to 3 will be the basis for model development, calibration, and validation in Task 4. THMC constitutive laws will be deduced based on the data obtained in Tasks 2 and 3, and predicted by Fast Fourier Transform from the microstructural observations performed in Task 3. The constitutive laws will be implemented in two open-source THMC-coupled finite elements codes (Bil and OpenGeoSys) and validated on the experiments. The two numerical approaches will be compared with each other.