Anisotropy in permeability of peats in context of vacuum consolidation by vertical drains

Publication Title
Anisotropy in permeability of peats in context of vacuum consolidation by vertical drains

Abstract

Computing the ground settlement due to consolidation assisted by vertical drains involves using horizontal coefficient of consolidation, c_h, which couples vertical compressibility, m_v, with horizontal permeability, k_h. These coefficients reflect dominant modes of deformation (vertical) and seepage (horizontal), respectively. However, the deformation is not simply vertical when the applied load comes not just from the overburden pressure but also from the negative water pressure induced in the ground, as happens with the vacuum consolidation with vertical drains. Detailed analysis of multi-modal consolidation deformation requires an independent value of k_h, decoupled from m_v. A variety of attempts, such as horizontally (radially) drained isotropic loading, turned out to have their own shortcomings in determining the k_h values at different levels of stresses. This led the authors to turn back to a simpler constant-head permeability test, but with a number of improvements to the conventional method, including accurate cross-sectional area updating with image analysis and use of a flexible side boundary (rubber membrane) to prevent the preferential flow along the soil specimen surface. The results on two peats indicated that, evaluated at an identical void ratio, the horizontal permeability is greater than the vertical permeability by a factor of roughly two a ratio which agrees with our experience from back analysis of field observation. Interestingly, the initial permeability was not as variable as the initial density. It was also found that the difference in density due to the inherent non-uniformity and that caused by mechanical compression has very different impacts on the permeability.

Authors
Satoshi Nishimura; Shuntaro Tada; Nobutaka Yamazoe

Published In

International Conference on Advances and Innovations in Soft Soil Engineering (ICAISSE2026)

Theme

Multiphysics Behaviour

DOI
https://doi.org/10.53243/ICAISSE2026-45