Development of pore pressures by nonuniform electroosmosis in clays

A theory is presented for the development of nonuniform pore pressures during electrokinetic treatment caused by local deviations in the electric field intensity and soil surface chemistry. The electric field intensity and surface (zeta) potential are the driving parameters for electroosmosis in any local soil region; when these parameters vary with space, there is a nonuniform driving force that must be balanced by a decrease or increase in local pore pressure. The theory is derived for the case of a rigid capillary, and is based on the assumptions of incompressible flow, negligible consolidation, the Helmholtz-Smoluchowski equation, and constant hydraulic conductivity. Comparisons of the theory with laboratory measurements made by Eykholt in 1992 are presented for one-dimensional electroosmotic flow through saturated kaolinite plugs. Measurements of the net electroosmotic flow rate, pore pressure and electrical potential profiles, and hydraulic conductivity, can be used to assess, at least qualitatively, the relative contributions to electroosmosis in soil regions along the profile. The k(eo) profile simulations provided here did not correlate well with measured chemical profiles. Future success of the simulation strategy will likely depend on two factors: accurate electric field measurements and electrokinetic characterization of soil sections. (C) 1997 Elsevier Science B.V.