Using shear wave velocity and microstructure for investigation of Champlain clay anisotropy

Abstract

Shear wave velocity measurement is a powerful tool to study the dynamic behavior of soils, including maximum shear modulus (elastic stiffness). Understanding the relationship between elastic stiffness, shear wave velocity, effective stress and void ratio enhances the reliability of seismic design and interpretation in geotechnical practice. The laboratory measurements of shear wave velocity allow parallel monitoring of mechanical characteristics by means of conventional geotechnical apparatuses like a standard oedometer device. This dissertation focuses on the investigation of directional properties of the Champlain soft marine clay under 1D-consolidation testing. Naturally occurring cohesive soil deposits exhibit anisotropy ranging from slight to pronounced degrees. To characterize the anisotropic nature of soft marine clay deposits, a novel laboratory method was developed and employed to enable directionality measurements. Using a transducer system, shear wave velocities were measured on undisturbed specimens within an instrumented oedometer equipped with lateral strain gauges for K0 stress measured, while applying effective vertical stresses up to 1000 kPa. The shear wave velocities increased with stress level, reaching up to 200 m/s in the verticalhorizontal plane and 220 m/s in the horizontal-horizontal plane at maximum applied stress. These measurements were used to calculate cross-anisotropic stiffness at different stress levels. The results revealed that intact Champlain clays exhibit low to moderate anisotropy ratios (1.10-1.30), with higher variations observed at lower stress levels, particularly below the preconsolidation pressure. The effect of bedding layer characteristics was also studied through trimming and preparing specimens at different angles from 90 to 0 degrees. Results demonstrate a consistent pattern where anisotropy values at intermediate angles bridge the gap between vertical and horizontal directions. Another point of interest in this study was to develop the anisotropy investigations of these clay samples on a microscale. The clay platelets position and their rearrangement were studied in intact and consolidated specimens, respectively. Scanning electron microscopy as an imaging technique was conducted to take high-quality digital images from the clay surface utilized in 1D-consolidation tests. A MATLAB-based script was developed to quantify clay fabric orientation using SEM images, applying two different methods of quantification (FOCM-I and FOCM-II). Intact Champlain clay samples show a randomly oriented to loworiented association based on the anisotropy classification (anisotropy index ranges around 0.145 and 0.17). Initially random particle orientations in intact samples progressively align perpendicular to the vertical applied stress through 1D-consolidation process. A parametric study was conducted to examine the effects of key SEM parameters, including accelerating voltage (10-30 kV) and magnification (1000-7000x), on clay fabric anisotropy calculations discrepancies. An imaging technique was employed to enhance the reliability of anisotropy quantification through SEM image analysis while minimizing uncertainties in directionality calculations. A comparison of anisotropy determination with published data in both macro- and microscale revealed the relationship and dependency of anisotropy on overconsolidation ratio and stress history of marine and glacial clays.

Date	30 Nov 2025
Original language	American English
Awarding Institution	École de technologie supérieure
Supervisor	Yannic A. Éthier (Supervisor) & Mourad Karray (Co-supervisor)