Kaolin Response to Ionic Concentration Cycles at Zero Lateral Strain

Natural and engineered geosystems experience cyclic changes in pore fluid chemistry, which can alter the fabric and engineering properties of sediments. This study explored the macroscale response of remolded kaolin specimens subjected to ionic concentration cycles under constant vertical effective stress and zero lateral strain conditions and monitored the ensuing time-dependent changes in void ratio, shear wave velocity, electrical conductivity, and hydraulic conductivity. The complete test sequence lasted 17 months for each test, resulting in a total of six full cycles. The sediment response after fluid replacement was exponential over time; the characteristic response time was longer for electrolyte invasion than for deionized water freshening. Global trends across all cycles showed the accumulation of volume contraction, increased skeletal stiffness, and a decrease in permeability toward asymptotic trends. However, distinct changes occurred within each concentration-freshening cycle. In particular, the longitudinal permeability increased during electrolyte injection despite sediment contraction, suggesting the enlargement of preferential flow paths during high-concentration invasion. Volume contraction and stiffening resembled the effect of mechanical stress; the equivalent change in effective stress scaled with the square root of the electrolyte concentration. A first-order, macroscale analysis indicated that chemically induced strains scaled with specific surface area, were inversely proportional to the applied effective stress, and were reduced by diagenetic structuration. Specific surface area and liquid limit can serve as indicators of a multimineral soil’s sensitivity to changes in pore fluid chemistry.