Evaluation of Double-Vacuum Saturation in Triaxial Testing of Compacted Clay: A Comparison with Back-Pressure Methods
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Achieving full saturation in consolidated triaxial testing is challenging, especially for compacted and residual soils with low water content and complex microstructures. Conventional back-pressure saturation can cause disturbance and leaching, leading to unreliable results. This study evaluates the double-vacuum (DV) method to reduce sample disturbance and better preserve microstructure during testing of compacted kaolin clay. Two methods—back pressure (NV) and double-vacuum (DV)—were compared using the consolidated undrained triaxial test and micro-CT imaging. The DV method reached a Skempton B-value ≥ 0.95 at lower pressure (150-200 kPa) in 8 hours, while NV needed up to 450 kPa and 50 hours. The DV approach halved axial and radial deformation and resulted in lower changes in void ratio (De/e0 ≈ 0.055), indicating improved sample integrity. Micro-CT showed a more uniform pore distribution and lower residual porosity (0.43%) versus NV (1.04%). These results suggest the DV method is a more reliable, less intrusive way to prepare fine-grained soils for triaxial testing, with significant implications for geotechnical labs, especially where high-pressure systems are limited.
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