Electro kinetic geosynthetic structure

Details Electro kinetic geosynthetic structure Electro kinetic geosynthetic structure

2001-09-25

2004-05-18

Sandy, Robert J. (Department: 3677)

Hydraulic and earth engineering

Drainage or irrigation

Porous or apertured pipe, flume, or tileway

C405S036000, C405S015000, C405S129450, C405S129750

Reexamination Certificate

active

06736568

ABSTRACT:

The present invention relates to an electrokinetic geosynthetic structure, the use of the electrokinetic geosynthetic structure as an electrode and methods of improving consolidation and reinforcement of substrate and removal or electro-sorption, -adsorption or absorption of contaminates, from substrates or adding materials to substrates under the action of an electric field using an electrokinetic geosynthetic structure.
The use of geosynthetic materials for reinforcement or drainage purposes is established practice. The materials used are generally non-metallic and can take any form, the most common being strips, sheets and grids. They can be manufactured by any suitable method, such as knitting, weaving or needle punching. Geosynthetics, also known as and sometimes referred to as geotextiles, are typically referred to by their principle function for any particular application and since there are essentially five principle functions there are five types of geosynthetics. These are filtration, separation, membrane, drainage and in plane flow, and reinforcement geosynthetics.
Geosynthetics may also provide any combination of the above functions and the present invention can be used for all of these functions, for example in drainage and reinforcement of substrate material in the construction industry, and thus has numerous industrial applications
Electrokinetic geosynthetics (hereinafter referred to as EKGs) are electrically conductive geosynthetic or geotextiles. EKGs have an enhanced performance over non-conductive geosynthetics. EKGs, in addition to providing filtration, drainage and reinforcement can be enhanced by electrokinetic techniques for the transport of water and chemicals species within fine grained low
There is thus a need for an alternative EKG structure which is easy to manufacture, durable and has a wide variety of applications. This need is satisfied by the present invention.
According to a first aspect of the invention there is therefore provided an EKG structure comprising geosynthetic material associated with at least one conducting element wherein the structure comprises at least one core element substantially enclosed by at least one sheath, one or both comprising the geosynthetic material.
The geosynthetic may be suited as at least one reinforcement and/or drainage/in plane flow and/or filtration and/or separation and/or membrane element.
The sheath serves to protect the structure by increasing its durability and can facilitate transport and manufacture.
Reference herein to a geosynthetic sheath is to any substantially closed or enclosing structure such as a container or tube suited to contain or retain within it one or more core elements and which is suitably at least partially porous, discontinuous or comprises apertures for passage therethrough of charged fluids, particles and the like.
The core element may be of any configuration retained within the geosynthetic sheath. Preferably, the at least one core element is or comprises a continuous, ideally solid, monolithic or divided element. The core may comprise additional elements or components suited to the desired function, such as drainage or in plane flow channels, spacers, voids, reservoirs of or for materials substrate and the like. permeability substrates, which are otherwise difficult or impossible to deal with. In addition to conductivity, transivity, absorption, wicking, hydrophilic and hydrophobic tendencies may also be incorporated in the geosynthetic.
The ability of electrokinetic phenomena to move water, charged particles and free ions through fine-grained low permeability substrate is established. There are five principle electro kinetic phenomena: streaming potential, migration potential, electro osmosis, ion migration and electrophoresis. The first two of these phenomena are concerned with the generation of electrical potential due to the movement of charges and charged particles respectively. The remaining three are concerned with the transport mechanisms developed upon application of an electrical field across a substrate mass.
In practice, an electrical field is applied across a substrate mass using EKG or conventional electrodes. Cations are attracted to the cathode and anions to the anode. The three transport mechanisms are explained below.
In electro-osmosis, as the ions migrate they carry their hydration water with them and exert a frictional force on the water around them. Hence, there is a flow of water at both the anode and the cathode. In order to maintain a charge neutrality however, there are more cations than anions in the pore fluid of the substrate containing negatively charged particles. Therefore there is a net flow of water to the cathode. This electro osmotic flow depends upon the applied voltage gradient and the electro osmotic permeability of the substrate.
The application of an electrical field across a substrate mass causes migration of the free ions and ion complexes, which are present within the pore fluid, to the appropriate electrode. The average mobility of ions in substrates may be of the order of 5×10
−8
m
2
/Vs, which is an order of magnitude greater than the electro osmotic permeability. Hence, anions can usually overcome the electro osmotic flow and migrate towards the anode; this movement being known as electro migration or ion migration.
When a DC electric field is applied across a particulate suspension, (colloids, clay particles, organics) charged particles in suspension are electrostatically attracted to one of the electrodes and are repelled from the other. Positively charged particles are attracted to the cathode and negatively charged particles are charged to the anode. Most colloids are negatively charged and are therefore attracted to the cathode. This electrophoresis has found applications in the densification of sludges and mine tailings.
EKGs can take the form of single materials, which are electrically conductive, or composite materials, in which at least one element is electrically conductive, such that the EKG can function as an electrode. They can be of the same basic form as present day filter, drainage, separator and reinforcement materials, but offer sufficient electrical conduction to allow the application of electro kinetic techniques for ground improvement.
There are a number of materials which can be used to produce electrically conductive geosynthetics, such as carbon materials, conductive composites, polymers and metals in the form of fibres, strips, wires, elements, stitching.
GB 2 301 311 relates to improvements in geosynthetics and introduces EKGs. This prior art document discloses EKG structures including layers of drainage and reinforcement geosynthetics stitched together with conductive fibres. The reinforcement and/or drainage material may also be conductive.
Such layered designs, although suitable for many applications, can be limiting in some applications.
The core and sheath may comprise the same or different materials and may both comprise a mixture of materials. In the case where both are formed from substantially the same material, they simply provide an outer portion and solid body portion, portions distinguished by their respective functions.
In an EKG as hereinbefore defined the core element may comprise any functional element required for the EKG, whereby the EKG is suited to be (partially) immersed within the substrate to be treated, or it may comprise or (partially) enclose a substrate to be treated or other material for treating the substrate. For example the core element may provide any or all of the five principle geosynthetic functions, and additionally or alternatively may provide a conducting element and/or sorbing, adsorbing, absorbing or decontaminating element.
Reference herein to substrate is to soil, loam, earth, sod and other ground material including mixed ground material and waste material or a mix of ground material and any other material, sewerage, sludge, or other substance or mixture of substances to be treated.
The at least one conducting element may be provided in any conduct

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