Changes in the Permeability and Permeability Anisotropy of Reconstituted Clays under One-Dimensional Compression and the Corresponding Micromechanisms

It is important to assess the permeability characteristics of clays in the prediction of the postconstruction settlement of geotechnical projects on clay grounds. The coefficient of permeability in the vertical direction (k(v)) and horizontal direction (k(h)) of clays under different vertical effective stresses were measured using newly developed permeability test equipment to investigate the variations in the permeability and permeability anisotropy of reconstituted clays and their influential factors under one-dimensional (1D) compression. The evolution of the pore sizes and pore orientations was also investigated to clarify the corresponding micromechanisms. The test results showed that the permeability of the reconstituted clays was related to the mineral composition, clay content, void ratio, and clay fabric. The variations in k(v) and k(h) with the void ratio could be represented in terms of a linear e-log(k) relationship. Under the same strain, the values of k(h) were obviously larger than those of k(v), and the permeability anisotropy ratio (k(h)/k(v)) values increased from 1 to 2 with increasing vertical strain. For all the tested reconstituted clays, both k(v) and k(h) generally decreased linearly with decreasing cumulative pore volume. For different clays with the same cumulative pore volume, k(v) and k(h) decreased with an increase in the plasticity index. In general, the anisotropy index of the pores increased, and the main orientation angle of the pores decreased with increasing vertical effective stress. For a certain clay, the increase in permeability anisotropy with vertical strain resulted from the gradual development of microstructural anisotropy. The findings of this study may assist in the accurate prediction of the consolidation behavior of reconstituted clays with vertical and horizontal drainage.