Strength reduction method and its applications to collapse problems in geomechanics

This thesis presents a comprehensive study on the stability analysis of retaining structures and slope stabilization systems by integrating the Strength Reduction Method (SRM)—redefined in this thesis as the Resistance Reduction Method (RRM)—with Finite Element (FE) analysis. The research focuses on three critical systems: gravity retaining walls, embedded cantilever retaining walls (ECR walls), and pile-reinforced slopes (PRSs). By addressing limitations of traditional design methods—which often rely on predefined failure mechanisms and simplified material models—this work aims to provide a more accurate assessment of structural stability.

In the first part, the stability and factor of safety of gravity retaining walls are investigated using SRM-based FE analysis with advanced Two-Surface Plasticity (TSP) constitutive models. The study evaluates the minimum backfill relative density and wall width required for stability across various wall heights. The analyses do not presume specific failure modes; instead, collapse mechanisms emerge naturally from the simulations. Factors of safety calculated are compared with those from traditional limit equilibrium methods, revealing differences and offering practical implications for design.

In the second part, the stability analysis of ECR walls is conducted using the Resistance Reduction Method (RRM), which we introduce in this part to distinguish our approach from the traditional SRM. The RRM entails reducing the system's overall resistance by modifying soil properties, structural geometry, or other factors contributing to system stability. This underscores the comprehensive nature of our method, which addresses multiple aspects of soil-structure interaction to more accurately assess stability. Using RRM on ECR walls employs the TSP model to calculate the minimum embedment depth required for wall stability, considering various retained soil heights and soil relative density profiles. Comparisons with limit equilibrium analysis results and experimental data demonstrate the applicability of the method. The findings aim to assist in optimizing embedment depths, enhancing both safety and cost-effectiveness in design.

The third part explores the stability of PRSs using the RRM-FE approach. The study investigates soil-structure interaction across various pile spacing-to-diameter (s/D) ratios. The research provides a comprehensive validation strategy for RRM-based FE analysis through comparisons with conventional methods, offering insights into PRS mechanics and informing design strategies for slope stabilization projects.

Overall, this thesis applies numerical methods to analyze the stability of retaining structures and slopes, offering a more realistic assessment without relying on predefined failure modes. The findings have implications for the design and construction gravity retaining walls, ECR walls, and PRSs, with potential improvements in structural stability and design optimization.