The development of stagnant pore water pressures due to non-uniform and non-steady distribution of voltage gradients were investigated in high water and salt content clay slurry using a floor-scale apparatus. The experiment was intended to simulate electrically enhanced dewatering of sea harbor sediments by horizontal drainage towards vertically installed electrodes. The scale of the test apparatus allowed for accurate measurements of the spatial and temporal variations of water pressure head, temperature, electrical potential and current throughout the test duration of 5 weeks. The pore water pressure dissipation measured at one-third the depth of the clay bed from mud-line appeared to alternate in rate and magnitude between the equally separated adjacent probe-stations, before it ceased completely. The voltage gradients between these stations fluctuated in the similar alternating manner indicative of significant variations in the local electro-osmotic water mass transport: rates among the regions. It is postulated that the non-uniform voltage gradients give rise to competing pressure gradients: and the electrical potential applied orthogonal to the settling direction polarize clay particles hence disrupting the dewatering process by pore water pressure dissipation and compaction in high salt content clay sediments. (C) 2011 Elsevier B.V. All rights reserved.