Field Applications of Electroosmosis To Increase Offshore Pile Driveability
Authors: Rose W.L. , Grubbs B.R. 
Published: December 2007

To reduce pile-driving resistance, electroosmosis has been employed successfully on driving various steel pipe piles for marine facilities. The method used was simply applying an electrical charge to the pile tip so that the surrounding water migrates to the tip for lubrication during driving operations. Observations, data, applicability, and cost-saving information are presented.

Introduction

Electroosmosis is defined as the movement of water through a porous medium, such as soil, by the application of an externally applied electrical potential. Negatively charged soil particles are surrounded by pore-water fluid that lies within the double layer pore-water fluid that lies within the double layer and/or in the unbound or free-water zone. Application of a direct current moves a portion of the pore water in the double layer and any free water pore water in the double layer and any free water toward the negatively charged electrode. The method is most effective in fine-grained, cohesive (clay) sediments because of their physiochemical characteristics.Foundation engineers have taken advantage on a limited basis of the electroosmosis phenomena to alter the engineering properties of soils. Primary uses have been in dewatering excavations, improving slope stability, and increasing bearing capacity. Dewatering applications involve placing a series of metal rods and perforated pipes vertically in the soil and connecting one or more DC generators to these "electrodes." The positive terminal is connected to the rods, known as anodes, and the negative terminal is connected to the perforated pipes, referred to as cathodes. Application of a DC potential forces the water in the soil voids to migrate toward the cathodes, where it is collected and pumped away. There is a consequent increase in soil moisture content at the cathode and a decrease at the anode.It was experience with electroosmostic dewatering that led to considering the process for driving piles. By making a pipe the cathode during driving, skin friction could be reduced; after driving, the skin friction could be restored by either turning off the current and waiting a sufficient time or by reversing the polarity and speeding up the natural "setup" process. Experimental field and laboratory tests process. Experimental field and laboratory tests using electroosmosis for pile driving have been demonstrated by Begemann and Nikolaev.As noted previously, the main problem with the potential of electroosmosis for offshore pile driving is the insulation required for piles installed through surface water. Surface water presents a path of least resistance that can short out a system with uncoated piles, with the result that very little, if any, piles, with the result that very little, if any, benefit is achieved in pile driving or pile setup. The method moves water through the soil vertically rather than horizontally.In Fig. 1, a steel pipe pile is shown that has an insulating coating on the outside surface. During driving, the negative lead from the DC source is attached to the top of the pile, and the positive lead is attached to an anode lying in the surface water at the mudline and near the pile. The interior of the steel piling and the uncoated pile tip are negatively piling and the uncoated pile tip are negatively charged. The tendency is for surface water and soil pore water to migrate down the pile exterior toward pore water to migrate down the pile exterior toward the tip.

JPT

P. 563