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Abstract An experimental apparatus affecting the expandability of montmorillonitic soft rock particles under electrochemical treatment has been developed；experimental study of the subsidence and expandability of soft rock particles affected by distilled water，NaCl solutions，NaCl electrolyte concentrations and electric gradients is carried out. The experimental results are as follows：the treatment of direct current can change subsidence rate of soft rock particles in distilled water but its volume expandability is not affected when the subsidence is in stable state. With increasing in NaCl electrolyte concentrations，the subsidence rate of soft rock particles increased and then the swelling ratio declined of negative index while the subsidence was finished. On the basis of the stabilization and then addition of the electric gradient of 0.5 V/cm，sample volumes decrease，and the swelling ratio of soft rock particles has the same variation with above mentioned. It seems that the electric gradient of 0.5 V/cm can provide sufficient electromotive force for the subsidence and the expandability of soft rock particles. Increment of electric again gradient can not affect the volume expandability of samples in stable state after the electric gradient of 0.5 V/cm applied. With the increment of electrolyte concentrations，both electrical currents of soft rock particles and temperatures of the experimental system increased with the treatment time，both electrical currents and temperatures reduced because electrolyte concentrations weakened. During the electrochemical treatment，electrode reactions and electrolysis have been observed. It caused the variance of pH values of soft rock particles. pH value decreases in the anodic region which is acid while pH value increase in the cathodic region which is alkaline.
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Received: 14 January 2009
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