Permeability anisotropy of natural clays as a function of strain

Abstract

Seven series of tests have been performed on specimens from five natural soft clay sites to determine the variation of the vertical and horizontal permeabilities when the soil is unidimensionally compressed. The results show that the permeability anisotropy does not increase significantly with compression up to strains of 25% for marine clays. In varved clays, mostly because the clay laminae are more compressible than the silty laminae, the anisotropy increases with vertical compression. Key words: permeability, clay, anisotropy, laboratory, compression.

Muds and mudstones: physical and fluid-flow properties

“…Anisotropies are less than 3 for natural clays and kaolinite, but is 8 at a porosity of 60% for pure Ca montmorillonite. These values are similar to previously published values (Tavenas et al 1983;INTRODUCTION A1-Tabbaa & Wood 1987;Leroueil et al 1990), but much less than those predicted from models in which clay plates become increasingly aligned with increasing stress (up to 100; Arch & Maltman 1990). Photomicrographs suggest that compaction-driven reorientation of clay plates is not easy and that directional permeability is not simply controlled by levels of average particle orientation.…”

Permeability anisotropy and resistivity anisotropy of mechanically compressed mudrocks

“…Some have found that mudrocks can remain isotropic (rk = kh/kv = 1) despite increasing compression (e.g. Clennell et al, 1999, Dewhurst et al, 1996, Basak, 1972, Leroueil et al, 1990 whereas other experiments showed permeability anisotropy develops with increased compression (e.g. Clennell et al, 1999, Basak, 1972, Leroueil et al, 1990) and with shear (e.g.…”

“…Clennell et al 1999, Leroueil et al 1990, Basak 1972and Yang and Aplin 1998. These studies used a variety of measurement techniques to measure the permeability anisotropy development in either resedimented, remoulded or intact mudrocks with increasing mechanical compression.…”

“…Leroueil et al 1990;Basak 1972) or a constant flow test (e.g. Clennell et al 1999, Dewhurst et al 1996, Bolton et al 2000 performed on two specimens of the same material oriented in different directions.…”

“…Leroueil et al, 1990, Dewhurst et al, 1996 suggested that small measured permeability anisotropy increases or decreases may in fact be due to specimen variability stemming from measurement techniques requiring the use of two separate specimens. Two studies applied experimental techniques requiring only 1 specimen.…”