Electro-osmotic properties and effects of pH on geotechnical behaviour of peat

Peat is an accumulation of partially decayed vegetation matter with high non-crystalline colloid which is formed in wetland systems. Using electro-osmotic techniques to improve peat entails developing a fundamental understanding of the electro-osmotic environment in peat which is an excellent context for this study. Electro-osmotic properties, electro-osmotic experiments, and the physicochemical effects on the peat due to electro-osmotic treatment were investigated. In addition, chemico-geomechanical sensitivities of peat to pH gradients were examined. The electro-osmotic properties of peat in the presence of different cations were also modeled by means of artificial neural networks. Soil samples were collected to evaluate the correlations between electro-osmotic parameters. Electro-osmotic apparatus were designed and developed specific to provide conditions to get a good quality of undisturbed non-homogeneous samples. Electro-osmotic experiments were then conducted on the peat. To determine the physicochemical effects on the peats due to electro-osmotic treatment, different undisturbed specimens were treated for short and long periods of time in the presence of peat water. Since the foremost effective mechanism during electro-osmotic treatment was electrolysis reactions at the electrodes, chemico-geomechanical sensitivities of peat to pH gradients were also investigated in the process. A backpropogation neural network was applied to model the electro-osmotic properties. The results of the study showed that the zeta potential, specific surface area, water contents, and liquid limit increased as the organic content increased. The negative charge in peat was highly pH-dependent and surface charge dropped to zero at pH 2.3 to 3.5. The zeta potential of the peat was affected by the type of cations, the pH, the valance of cations, the concentration of the cations, degree of humification, and hydrated radius of the cations. The greater degree of humification resulted in the higher zeta potential. The trivalent cations showed a higher power in decreasing the zeta potential. The lower hydrated radius when the cations had the same valance showed a higher power in the decrease of the zeta potential. The higher concentration of the cations resulted in the lower zeta potential. The peat with the higher water content, temperature, and porosity showed the lower resistivity, while the higher organic content showed a contrary effect. The resistivity decreased as the degree of humification increased. The study revealed that the greater degree of humification resulted in higher electro-osmotic permeability. The electro-osmotic treatment strengthened the peat at the anode. The undrained shear strength and liquid limit of the peat were improved and the cation exchange capacity and zeta potential decreased as the pH decreased. The undrained shear strength and liquid limit decreased and the cation exchange capacity and zeta potential increased in the vicinity of the cathode. Chemico-geomechanical effects of peat water pH gradients on peat revealed that in both fibrous and amorphous peat, the permeability and coefficient of volume compressibility increased and optimum moisture content decreased because of the acidic conditions, while the basic conditions had a contrary effect. The peats did not show any positive surface charge even at very low pH. The sensitivity of the amorphous peat to the electro-osmotic environment was higher than the sensitivity of the fibrous peat to the pH gradients. Electro-osmotic environment resulted in the charge neutralization, and increased the potential ability of the peats for a mechanical densification. The artificial neural networks results were found to be close to test values.

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