Sampling Disturbance Effects on Deformation and Strength Properties of Coode Island Silt

This study investigates sampling disturbance effects on deformation and strength properties of Coode Island Silt (CIS), a problematic soft soil in Melbourne, Australia. Samples were obtained using Shelby tube, BIT 100mm (modified fixed-piston), and Block samplers. Incremental loaded oedometer, multi-stage stepwise creep, and anisotropically consolidated undrained triaxial compression tests were conducted to quantify sample disturbance effects. Creep tests are particularly important due to limited research on sample disturbance effects on creep deformation, as CIS is prone to significant creep. Results show that sampling disturbance significantly reduces deformation parameters (compression index: 58%, yield stress: 38.6%, peak creep index: 26%) and undrained shear strength (12%) when comparing samples with the highest and lowest quality. Block samples achieved the highest quality (Good to fair), followed by BIT 100mm (Poor), and Shelby tube (Very poor), based on Lunne’s Δe/eo criterion. Using the test results and a database from reported studies, a regression model was proposed to predict sample disturbance effects on key deformation and strength parameters considering sampler geometry, soil properties, stress state, and sample quality. The model allows correction of tube/piston-sample results to equivalent Block-sample quality, providing a practical method for estimating consolidation and strength properties when high-quality Block samples are unavailable.