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

碳酸盐土壤覆盖了世界40%以上的海床，海上结构物、管道、人工岛和其他海洋结构物都是在这里建立的。在大多数情况下，碳酸盐土壤是生物起源的，包括小型生物的骨架和外壳，即贝壳碳酸盐砂体。这些土壤是一种复杂且鲜为人知的材料，80年代平台安装过程中发生的一些事故就证明了这一点。因此，在大多数设计指南中，雪利砂都被归入了“问题土壤”这一特殊类别。虽然现在失败的情况相对较少，但通常使用保守的方法和高的安全系数。了解壳状碳酸盐砂岩的特性对于设计近海结构的基础是至关重要的。特别是，理解微观尺度上发生的物理现象有可能刺激稳健计算方法的发展，将其整合到新的或现有的设计方法中。基于图像的地质力学是一个迷人的研究领域，有可能改变土壤的研究和建模方式。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。这项研究利用四维同步辐射x射线成像和后处理技术研究了壳状碳酸盐岩砂体在压缩条件下的运动学和应变图。这一结果将有助于科学地理解壳碳酸盐岩砂岩的多尺度行为。这将形成开发织物信息本构模型的基础，以更好地预测土体响应，从而改进海上结构物基础的设计实践。该项目的目标是促进更安全、不那么保守和更可持续的地面结构，并减少在建造海上基础期间因不可预见的地面反应而产生的财务风险。这里开发的这种多尺度方法和图像算法，将对广泛的颗粒媒体社区模拟添加剂制造、采矿、食品和制药行业的机械过程具有重要价值。

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.