New technology from Electrokinetic has delivered significant benefits in terms of both efficiency and cost when applied to historically difficult ground engineering and dewatering problems.
The patented technology, electrokinetic geosynthetics (EKG), has numerous applications across a range of industries including stabilisation of embankments and cuttings; dewatering of wastes such as sewage sludge and mine tailings; and sports turf management.
With the advent of EKG, active geosynthetics are now a viable tool for design and process engineers and manufacturers.
Traditional geosynthetics and industrial textiles are used in the civil, mining, environmental and waste engineering industries to carry out a range of functions including drainage, reinforcement, filtration, separation, containment, encapsulation and sorption.
All of these functions, in one way or another, are influenced or limited by the rate at which water is able to flow through the materials with which the geosynthetics are being used to improve or treat.
In use, most geosynthetics play a passive role for example, geomembrane barriers stop the passage of liquids; soil reinforcement provides tensile resistance, but only after an initial strain has occurred; and drains provide a passage for water but do not cause the water to flow towards the drain.
New applications for geosynthetics have been identified if they can provide an active role, initiating biological, chemical or physical change to the matrix in which they are installed as well as providing the established functions.
This can be achieved by combining the electrokinetic phenomena of electroosmosis, electrophoresis and associated electrokinetic functions such as electrolysis with the traditional functions of geosynthetics of drainage, filtration, containment and reinforcement to form electrokinetic geosynthetics (EKG).
The diagram left characterises the electrokinetic processes that are activated when ground is treated with EKG materials. These include:
• Electroosmotic flow from the anode areas towards the cathode
• Pore pressure reduction spreading out from anodes
• Cementation around the anodes
• Precipitation around the cathodes
The key consequence of harnessing these effects is the overall strengthening of the ground.
Reductions in porewater pressure and electroosmotic flow are given by equations 1 and 2.
u = - ke/kh. gw. V Equation 1 (Mitchell, 1993)
Q = ke.V/L. A Equation 2, (Mitchell, 1993)
Where: u = porewater pressure; ke = coefficient of electroosmotic permeability;
kh = coefficient of hydraulic permeability; gw = density of water; V = voltage applied between electrodes;
Q = electroosmotic water flow; L = spacing between electrodes (anode – cathode); A = area
During soil treatment, electroosmotic flow is independent of hydraulic permeability and the degree of negative porewater pressure or suction that builds up is proportional to the ratio of the coefficients of electroosmotic and hydraulic permeabilities. Therefore, electroosmosis is most effective in fine grained soils such as clays and silts.
In addition the soil between the electrodes can be further improved by the use of chemical conditioners, whose application is ideally facilitated by the design of EKGs.
All of these effects can be used in various combinations in ground engineering settings including slope stabilisation, ground consolidation, construction of reinforced soil and sports turf conditioning.
General features of EKG technology
• Active water flow through clays
• Long term (post – EK treatment) drainage
• Long term (post EK-treatment) reinforcement
• Enhanced soil –reinforcement bond
• Reduction in shrink swell behaviour
• Rapid increase in undrained shear strength
• Permanent increase in drained shear strength
• Improvement conditioning of clay minerals by electrokinetic ion migration, which achieves much higher transportation rates than either conventional hydraulic or electroosmotic flow mechanisms
Benefits of EKG technology
• No requirement for large plant
• Greatly reduced access considerations
• No need for large volume material haulage
• Require minimal levels of manning and supervision
• Rapid deployment
• Reduced overall project time
• Permits use of conventionally unacceptable material
• Lower the environmental footprint
• Reduced overall project costs
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Electrokinetic is a trading name of Central Alliance Pre Construction Services Limited, Alliance House, Junction 41 Business Park, South Park Way, Wakefield, WF2 0XJ