Multiscale and probabilistic modelling of progressive slope failure

在英国和全球，各种规模的斜坡坍塌正在严重影响弹性城市的可持续发展，因为它的发生会严重威胁人口、基础设施、公共服务和环境。例如，英国地质调查局估计，英国10%的斜坡被归类为中度至严重山泥倾泻风险，超过7%的主要交通网络位于这些地区。这些斜坡可能会在长时间的潮湿天气或较强烈的短期降雨事件中坍塌。到目前为止，公众对边坡失稳风险的认识很高，但对其基本失稳机理和对策的了解还很有限。这主要是由于在分析多尺度响应和表征斜坡材料特性的空间不均一性方面存在困难。用成熟的经验模型进行的实验室和数值研究可以解释某些特定的边坡失稳事件的一般特征，但不能普遍适用。一些具有挑战性的问题需要解决，例如i)如何开发具有多尺度建模能力的可靠数学模型来分析斜坡的渐进性破坏？二)如何处理真实斜坡的空间变异性和不确定性，例如材料特性、裂缝、流体渗透性？3)如何准确估计滑坡的蔓延及其对基础设施的影响？这些挑战的基本科学问题是不同尺度的不均匀斜坡的弱化机制，因为它决定了不同地质和环境条件下的斜坡响应。拟议的研究旨在通过多尺度和概率模拟的方法来探索渐进性斜坡破坏的基本机制及其对基础设施的影响。它可以方便地将边坡的大变形问题作为边值问题(BVP)进行有限元分析，而土体的局部破裂、开裂或不连续性态则可以通过DEM在较小的离散子域上通过颗粒力学来计算。DEM拼接的边界条件是由有限元网格的整体变形导出的。在分析中，土/岩石的性质(如弹性模数、摩擦系数、强度和流体渗透率)将被评估为具有空间变量的随机场。数值模拟可以有效地弥合微观材料特性与整体宏观边坡响应之间的差距。在数值模拟中，可以有效地研究材料的不均匀和不连续对边坡破坏和随后的滑坡扩展的贡献。当加载应力超过颗粒在微观尺度上的粘结强度时，内部断裂就会自然发生，这避免了在传统的连续介质模拟中使用一些唯象本构关系。作为一项多学科的研究，该项目将涉及岩土工程、计算岩土工程、地质学、统计学、土岩力学和颗粒力学等学科。拟议的数值模型将通过提供有效和可靠的数值模拟方法，使土地规划和管理方面的所有研究人员和利益攸关方受益。这将为滑坡风险评估、减灾和长期土地管理提供支持，从而实现环境、社会和经济效益。因此，决策者将对斜坡失稳风险评估更有信心，作为基础设施投资考虑的基础。因此，可以实施危险预警系统、保护措施和土地利用条例，从而可以最大限度地减少生命和财产损失，而不需要投资于长期、昂贵的地基加固项目。

In the UK and globally, the slope failures of various sizes are crucially affecting the sustainable development of resilient cities, as its occurrence can significantly threaten the populations, infrastructures, public services, and environment. For example, the British Geological Survey has estimated that 10% of slopes in the UK are classified as at moderate to significant landslide risk, with more than 7% of the main transport networks located in these areas. These slopes may fail during prolonged periods of wet weather or more intensive short duration rainfall events. To date, the public awareness of slope failure risk is high, but our understanding of its fundamental failure mechanism and countermeasures are still very limited. This is mainly due to the difficulties in analysing the multiscale responses and characterize the spatial inhomogeneity of material properties of slopes. Laboratory and numerical investigations with well-developed empirical models can explain the general features of some specific slope failure events but cannot be applied universally. Some challenging issues need to be addressed, such as i) How to develop reliable mathematical models with multiscale modelling capability to analyse the progressive failure of slopes? ii) How to address the spatial variabilities and uncertainties of real slopes, e.g. material property, fractures, fluid permeability? iii) How to accurately estimate the spreading of landslide and its impact on infrastructures? The fundamental scientific issue of these challenges is the weakening mechanism of inhomogeneous slopes at different scales as it determines the slope responses under various geological and environmental conditions.The proposed research aims to explore the fundamental mechanism of progressive slope failure and its impacts on infrastructures via a multiscale and probabilistic modelling approach. It enables the large deformation of slopes to be conveniently analysed by FEM as boundary value problem (BVP), while the local fracturing, cracking, or discontinuous behaviours of soil to be evaluated in smaller discrete subdomains through granular mechanics by DEM. The boundary condition of DEM assembly is derived from the global deformation of FEM meshes. In the analysis, the soil/rock properties (e.g. elastic modulus, friction coefficient, strength, and fluid permeability) will be evaluated as random fields with spatial variabilities. The numerical modelling can effectively bridge the gap between the microscopic material properties and the overall macroscopic slope responses. In the numerical modelling, the contributions of material inhomogeneity and discontinuity to slope failure and subsequence landslide spreading can be effectively investigated. The internal fracture would occur naturally when the loading stress exceeds the particle bonding strength at the microscale, which avoids the use of some phenomenological constitutive laws in conventional continuum modelling. As a multidisciplinary research, this project will involve the subjects of geotechnical engineering, computational geotechnics, geology, statistics, soil/rock mechanics and granular mechanics. The proposed numerical model will benefit all researchers and stakeholders in land planning and management by providing efficient and reliable numerical modelling approaches. This will support the landslide risk evaluation, hazard mitigation and long-term land management, from which the environmental, social, and economic benefits can be achieved. As a result, the decision makers would have greater confidence in slope failure risk assessments on which they are basing their infrastructure investment considerations. Consequently, hazard warning systems, protections and land utilization regulations can be implemented, so that the loss of lives and properties can be minimized without investing in long-term, costly projects of ground stabilization.