Effect of Swelling during Specimen Preparation on Shear Behavior of Overconsolidated Onsøy Clay

ABSTRACT The integrity of an intact sample significantly depends on maintaining the water content of the extracted soil until laboratory testing. Particularly, when exposed to water, overconsolidated clays tend to absorb and volumetrically swell. Traditional methods, such as using wet porous disks, allow specimens to rapidly absorb available water upon contact, potentially altering the intact soil structure and thus its mechanical behavior. This means that unnecessary swelling of the clay specimens should be avoided during specimen preparation for soil element testing. This paper investigates the influence of cell pressure confinement during the introduction of water to drainage lines and initially dry filter stones on subsequent shear behavior through a series of controlled laboratory experiments that were conducted using reconstituted Onsøy clay specimens following ASTM D4767-11, Standard Test Method for Consolidated Undrained Triaxial Compression Test for Cohesive Soils guidelines. Various confining stresses were applied during initial flushing of the drainage lines: the swelling pressure inhibiting specimen expansion (120 kPa for OCR2 and 355 kPa for OCR4 specimens) and 5 kPa of mean effective stress allowing the specimen swelling. After consolidation, undrained shear compression tests were conducted, and the mechanical behavior was recorded, including stiffness, strength, and excess pore water pressure. Results revealed significant differences in mechanical behavior among specimens, suggesting that allowing free swelling of intact specimens could have detrimental effects on soil properties. This study underscores the importance of controlling swelling of overconsolidated specimens due to absorption and highlights the potential impact on soil shear behavior.