Influence of Discontinuous Joints on Permeability

Abstract

Extensive jointing is a fabric feature that is common to many finegrained soils with high clay content. Both naturally occurring and recompacted soil deposits have been known to exhibit extensively jointed fabrics. Jointing has been shown to dramatically influence the nature of the flow of fluids through jointed soils. Field permeability tests have demonstrated permeabilities of several orders of magnitude higher than laboratory tests of intact samples of the same material. The purpose of this study is to investigate the influence of joints on permeability in a low‐permeability matrix in which the joints are not necessarily continuously connected. This was accomplished by performing permeability tests on oriented samples of remolded fine‐grained till that had been isotropically consolidated and by comparing these results with finite element models. The soil was obtained from the Lake Michigan shoreline in the state of Wisconsin. This soil has been found to be extensively jointed, perhaps due to post‐glacial stress relief. A spherical sample of this soil was consolidated and tested at various orientations to obtain an intact matrix permeability. The specimen was then artificially jointed through the incorporation of a porous plate within the specimen. Additional permeability tests were performed at various orientations in order to investigate the influence of joint orientation on apparent permeability. The results indicated that the permeability in the direction parallel to the joint was significantly greater than the permeability perpendicular to the joint. The apparent permeability decreased rapidly as the applied gradient became more perpendicular to the joint, approaching that of the intact matrix. Similar results were obtained from a finite element model of the jointed spherical specimen.