Direct and Indirect Permeability of Fissured Tills

Comparison of direct and indirect measurements of water permeability on relatively large undisturbed and compacted Scottish till specimens in rigid-wall (Rowe cells) and flexible-wall (triaxial cells) permeameters shows the interaction of macro-fabric, test method, evaluation basis, effective stress, and possibly sidewall leakage. At low stresses, the sidewall leakage in a Rowe cell is the most likely cause of the directly measured permeability, k_d, and pore-pressure-dissipation-based permeability, k_p, becoming higher than settlement-based permeability, k_s. Similarly, fissures raise permeability measured in both permeameters. Generally, k_p is higher than k_s (or volume-change-based k_v from triaxial cells) with k_a in between but closer to k_s (or k_v). The differences decrease with increasing stresses; the reduction rate for fissured specimens is dependent on fissure coating thickness and permeability.