Advanced Interaction Analysis for Foundation Design and Coastal Cliff Stability

Abstract Background Coastal cliff environments present complex geotechnical and structural challenges arising from the combined effects of soil behaviour, wave loading, and progressive cliff erosion. The stability of these areas is critical for the safety and sustainability of coastal infrastructure. Current approaches often fail to fully integrate the coupled effects of hydrodynamic forces, soil response, and structural interaction. This research addresses this gap by developing an integrated analytical and numerical framework capable of simulating fluid-cliff interaction (FCI) and fluid–cliff–foundation interaction (FCFI) and identifying the critical zones in failure and critical construction distance from the cliff crest, beyond which the impact of wave action on foundation performance becomes negligible. Methodology A comprehensive mixed-method approach was adopted, combining advanced numerical modelling, experimental investigation, and field data analysis. The research was conducted through three complementary studies: 1)Structure–Soil–Structure Interaction (SSSI): Finite element modelling was used to evaluate how adjacent buildings affect one another’s foundations under varying subgrade reaction modulus (Ks), as outlined in chapter 3. 2)Wave–Cliff Interaction: The mechanisms driving cliff instability under wave impact were examined using an experimental wave flume, supported by three-dimensional numerical models incorporating fluid–structure interaction (FSI) principles. This phase, presented in chapter 4, identified the critical cliff profiles most prone to wave-induced failure. 3)Cliff–Foundation Interaction and Critical Distance: The final component, detailed in chapter 5, developed a methodology to quantify the critical distance from the cliff crest by coupling hydrodynamic loading, soil deformation, and structural response. Model validation was achieved through comparison with field data from Sidmouth, UK. Parametric and sensitivity analyses using the Random Parameters Method (RPM) and Strength Reduction Method (SRM) were employed to identify the most influential soil and material parameters affecting overall stability. Key Findings Incorporating variable subgrade reaction moduli (Ks) in foundation design allows for a more realistic representation of soil–structure interaction. By assigning different Ks values to different regions of the foundation, designers can account for spatial variability in soil stiffness, improving load distribution and minimizing potential settlement or localized overstressing. The experimental and computational results identified soil density, cohesion, and internal friction angle as the dominant parameters influencing cliff retreat and failure modes. Moreover, SSSI exhibited a dual role: it reduced stability in soft soils but contributed positively to stiffness and stress redistribution in hard soils. This finding underscores the importance of site-specific soil characterization in foundation design for coastal regions. The research established that, for the Sidmouth cliff profile examined in this study, wave action significantly amplifies deformation and stress within foundations located within approximately 12 m of the cliff crest, identifying this distance as the critical threshold for safe construction under the given geological and hydrodynamic conditions. Beyond this range, wave-induced and hydrodynamic effects were found to diminish markedly. Contributions This thesis delivers a novel, validated, and adaptable framework that integrates SSI, SSSI, FSI, and FCFI within a unified analysis platform. The key contributions include: •Establishing a quantitative critical distance from the cliff crest to guide safe building placement. •Demonstrating the interactive effects of wave energy, cliff morphology, and soil–foundation behaviour. •Introducing an optimised design approach using variable subgrade stiffness to enhance the accuracy of foundation modelling. •Providing a scientific basis for coastal planning and setback policy formulation. Collectively, the findings advance understanding of coupled geotechnical–hydrodynamic–structural interactions in coastal environments. The developed framework supports the design of resilient coastal infrastructure, promotes sustainable urban planning, and informs evidence-based coastal management strategies for erosion-prone regions.<p></p>

Author dc:creator

• Ali Khosravifardshirazi (21060026)

• Structure-Soil-Structure Interaction (SSSI)
• Fluid-Structure Interaction (FSI)
• Fluid-Cliff-Foundations Interaction (FCFI)
• subgrade reaction modulus
• foundation design
• finite element method
• cliff analysis
• critical zone of failure

Statement dc:rights

• All rights reserved

Identifier

10779/exe.31611463.v1

OAI identifier oai:identifier

oai:figshare.com:article/31611463