Multiscale modelling of shelly carbonate sands for foundation design of offshore structures (MuMShell)

碳酸盐土壤覆盖了世界上40%以上的海底，海洋结构、管道、人工岛和其他海洋结构都是在这里建造的。在大多数情况下，碳酸盐土壤是生物成因的，包括小生物的骨架体和壳，壳状碳酸盐砂。这些土壤是一种复杂且知之甚少的材料，正如80年代平台安装期间报告的许多事故所证明的那样。因此，在大多数设计指南中，贝壳砂被归入“问题土壤”的小生境分类。虽然故障现在相对罕见，但通常使用保守的方法和高安全系数。了解贝壳状碳酸盐砂的特性对于海上结构物基础设计至关重要。特别是，了解发生在微观尺度的物理现象，有可能刺激强大的计算方法的发展，将集成到新的或现有的设计approaches.Image-based地质力学是一个迷人的研究领域，有可能改变土壤的方式进行调查和建模。在微观尺度上跟踪变形的能力有助于回答有关在宏观尺度上观察到的土壤行为的基本问题。该研究采用4D同步辐射X射线成像和后分析，调查的运动学和压缩下的贝壳碳酸盐砂的应变图。研究结果将有助于对贝壳状碳酸盐砂多尺度行为的科学认识。这将成为开发织物本构模型的基础，以更好地预测土壤响应，从而改善海洋结构物基础的设计实践。该项目的目标是促进更安全、更保守和更可持续的地面结构，并减少海上基础施工期间与不可预见的地面反应有关的财务风险。本文开发的这种多尺度方法和图像算法对于广泛的颗粒介质社区模拟增材制造，采矿，食品和制药行业的机械过程将是有价值的。

Carbonate soils cover over 40% of the world's seabed, where offshore structures, pipelines, artificial islands and other marine structures are founded. For the most part, carbonate soils are of biogenic origin comprising skeleton bodies and shells of small organisms, the shelly carbonate sands. These soils are a complex and poorly understood material as evidenced by a number of accidents reported during platform installation in the 80s. As a consequence, shelly sands have been placed into a niche classification of "problematic soils" in most design guides. While failures are now relatively rare, conservative methods and high factors of safety are commonly used. Understanding the behaviour of shelly carbonate sand is critical for the design of foundations for offshore structures. In particular, understanding the physical phenomena taking place at the microscale has the potential to spur the development of robust computational methods to be integrated into novel or existing design approaches.Image-based geomechanics is a fascinating research field that has the potential to transform the way soils are investigated and modeled. The ability to follow deformation at the microscale has helped to answer fundamental questions about the soil behaviour observed at the macro-scale. The proposed research uses 4D synchrotron x-ray imaging and post analysis to investigate the kinematics and the strain maps of a shelly carbonate sand under compression. The outcomes will contribute scientific understanding on the multiscale behaviour of shelly carbonate sands. This will form the basis to develop fabric-informed constitutive models to better predict the soil response, thus improving design practices for foundations of offshore structures. The ambition of this project is to contribute towards safer, less conservative and more sustainable ground structures and reduce the financial risks associated with unforeseen ground response during construction of offshore foundations. This multiscale methodology and image algorithms here developed, will be valuable to the broad granular media community to simulate mechanical processes in additive manufacturing, mining, food and pharmaceutical industries.