A new flexible-wall triaxial permeameter for localized characterizations of soil suffusion

Suffusion involves the migration of fines within the soil matrix, which may cause many types of geohazards. Localized characterization of suffusion is necessary because suffusion is inhomogeneous. However, existing studies on localized characterization have primarily relied on rigid-wall permeameters, which prevent lateral soil deformation and might introduce preferential flow, biasing the experimental results. In this study, a new flexible-wall triaxial permeameter was developed for the localized characterization of suffusion. The permeameter testing system has four modules: a loading and permeating module, a pressurized water supply module, an outflow-collecting module and a back pressure supply module. The local porewater pressure was captured by an invented perforation socket that connected transducers to the specimen through the flexible wall without water leakage. The local deformation was measured by photography. Three repeated suffusion tests on complete decomposed granite were carried out using the new permeameter. The results show that the maximum coefficients of variation of the initial seepage velocity, clogging hydraulic gradient, critical hydraulic gradient and total loss of fine particles were less than 4.9%, demonstrating satisfactory reliability. Soil suffusion can be better characterized and understood when a localized indicator and a precursor for suffusion-induced failure are considered.