INNOVATIONS IN ONE-DIMENSIONAL CONSOLIDATION TESTING: A REVIEW OF THE DOUBLE-ACTION OEDOMETER

This study presents an in-depth evaluation of the double-action oedometer (DAO) as an advanced testing apparatus for simulating soil compressibility under near-field conditions. Unlike the classic oedometer, which enforces full lateral confinement and single-direction loading, the DAO introduces a dual-loading mechanism. A large platen simulates preconsolidation pressure σ’p, while a concentric piston does the incremental vertical loads, which in effect allows partial lateral deformation. The objective is to reflect the in-situ anisotropic stress paths so that post-test theoretical corrections could be minimised. Silty clay samples were tested using both the DAO and the classic oedometer. Compressibility parameters Eoed, Cc, mv and av were compared. The DAO results recorded higher stiffness Eoed = 10,867 kPa, reduced strain, and more realistic ei trends. The DAO Eoed in comparison with the classic gives M0 = 1.04, which is lower than the theoretical M0 from the correction coefficient in the NP 112/2014. These outcomes could indicate the overestimation of the M0 in theoretical standards. Additionally, the lower strain and settlement yields from the DAO testing under identical stress levels indicate reduced influence of sample disturbance. The apparatus effectively simulates the natural soil stress history and void ratio evolution. This leads to improved prediction of settlement and more accurate derivation of mechanical parameters used in design. The DAO demonstrates clear benefits for geotechnical modelling, offering a cost-effective alternative to classic and modified oedometers. Its potential for standardization and integration into geotechnical codes is significant