Basal Stability of Braced Circular Excavations in Isotropic and Anisotropic Clays

This study provides a comprehensive numerical analysis of the stability of basal heave in braced circular excavations in undrained soft clays. This analysis was conducted using the finite element method, focusing on both isotropic and anisotropic strength conditions. The initial study utilized the classic Mohr-Coulomb elastic-perfectly plastic constitutive model for isotropic, homogeneous strength conditions. This phase investigated the influence of excavation depth-to-width ratio (H/B), wall embedment depth (D), clay thickness (T), and soil-wall interface roughness (Rint) below the excavation. In the next phase of the study, the NGI-ADP anisotropic strength model was utilized. In this set of analyses, the anisotropy ratio (SuP/SuA), strength gradient (kH/Suo), initial mobilization ratio (τ₀/SuA) and Rint were identified as the key factors. Across a broad range of H/B ratios, both analyses show that narrower excavations exhibit superior resistance to basal heave, with failure mechanisms adopting different forms of localization for different conditions. The stability factor Nc was found to vary from 7.15 to 95.88 for the different analyses. Increased wall embedment depth and rougher interfaces provide more stabilizing, constraining failure surfaces, thereby, enhancing the factor of safety. Under anisotropic conditions, lower SuP/SuA ratios are associated with reduced stability, whereas higher kH/Suo ratios are indicative of stiffer profiles, which contribute to improved stability. The integration of these analyses, supported by the observed failure mechanisms and stability charts, elucidate the detailed relationships between the governing parameters and the basal stability. As part of this study, regression-based equations were derived, which can be employed as quick and reliable engineering tools for estimating basal stability.

Name thesis:degree_name

M Eng Sci

Discipline thesis:degree_discipline

Civil and Environmental Engineering

Grantor dc:publisher

The University of Western Ontario

Year dc:date.issued

2025

Author dc:creator

• Ara, Sabrin

Advisor dc:contributor.advisor

• Newson, Timothy, A.

• Basal heave stability
• Parametric analysis
• Stability factor
• Finite element method
• Shear strength reduction
• Regression-based equations.

Language dc:language.iso

en

Handle dc:identifier.uri

https://hdl.handle.net/20.500.14721/38564

OAI identifier oai:identifier

oai:uwo.scholaris.ca:20.500.14721/38564