Determination of consolidation parameters based on the excess pore water pressure measurement using a newly developed U-oedometer: Fid-Bau Portal

Determination of consolidation parameters based on the excess pore water pressure measurement using a newly developed U-oedometer

Chow, Jun Kang / Wang, Yu-Hsing / Lui, Hoi Lun / Huang, Erwin

Abstract

In this study, the U-oedometer, a novel modified oedometer cell equipped with tailor-made needle probes, is developed to easily and accurately measure the excess pore water pressure (Δu) during 1D consolidation tests and to determine the coefficient of consolidation (cv). The 3D printing technique is applied to make simple yet robust modifications to the conventional oedometer cell for facilitating the installation of the needle probes. The tailor-made needle probes are designed in such a way that the volumetric compliance is lowered to avoid measurement bias. Subsequently, the Δu-based method is proposed to determine cv, with the target of avoiding the intervention of human judgement and therefore minimizing the degree of subjectivity. The experimental results demonstrate that the measured Δu matches the theoretical values of the Terzaghi 1D consolidation theory, showing that the estimated cv is sufficiently reliable. In addition to the determination of cv, the U-oedometer allows additional measurements of other soil properties during consolidation, including the coefficient of permeability (k) and the coefficient of earth pressure at rest (K0). It is observed that k decreases with the reduction in void volume, due to the increase in the effective vertical stress (σv′). Further, the secondary compression seems to be a continuation of the primary consolidation, where the soil sample continues to deform at a relatively slower rate, associated with the slight decrease in k. A constant value of K0 is observed at any value of σv′ in the loading path, while during secondary compression, K0 slightly increases with time.