Electro-osmosis experiments were conducted on rigid cylindrical samples containing 0.01 M NaCl-water saturated Speswhite kaolinite. It is experimentally found that the electro-osmotic permeability is pH-dependent. It is also experimentally found that time and spatial variations of the sample pH and of the pore water pressure correlate. This is qualitatively confirmed by a simple analysis that couples the electro-osmotic and hydraulic flows through the pH-dependent electro-osmotic permeability. However quantitative agreement between the experimental and numerical values of the pore water pressure is not obtained throughout the whole sample. This suggests that the hydraulic permeability may also depend on the pH.