Undrained shear strength of clays as modified by pH variations

The undrained shear strength of clays is an important geotechnical parameter used during construction processes. Several laboratory tests were performed on kaolinite and smectite mixed with pore fluids with different pH values. Vane shear tests were carried out and it was found that the undrained shear resistance for clays increased considerably if the pore fluid had a high or a low pH. A possible explanation could be the dissolution of Al3+ which acts as a coagulant, increasing the internal shear resistance. Geochemical computations, Al measurements and ζ-potential experiments were performed to confirm this theory. The research suggests varying the pH may make a useful contribution to soil improvement techniques.