Integrated Apparatus for Measuring the Coefficient of Earth Pressure at Rest with Frictional Effects Analysis

The coefficient of earth pressure at rest K0 is a crucial mechanical parameter in geotechnical engineering analysis and calculations. Conventional oedometers make it difficult to measure radial stress and lack experimental testing of the friction between the instrument’s sidewall and the soil specimen. In this study, an integrated apparatus was developed, including a novel oedometer apparatus and an interface shear apparatus. The novel oedometer apparatus is a tall oedometer and the friction between the specimen and the sidewall of the oedometer was evaluated using the interface shear apparatus. This allowed for the derivation of a stress expression at any height within a dry soil specimen under lateral confinement conditions. Based on the stress-reduction relationship at different heights of the specimen, a testing expression for K0 was obtained. The impact of varying height-to-diameter ratios of the specimen and self-weight stress on the stress state profile in dry soil specimens was also investigated. The test results indicate that the friction coefficient between the sand and the sidewall is independent of the stress state, and K0 remains essentially constant throughout the loading process. For dry sand, variations in stress distribution along the height of the specimen are attributed to sidewall friction. The earth pressure coefficients obtained using the novel oedometer apparatus and the strain path-controlled triaxial apparatus in this study align closely with Jaky’s theoretical formula.