GB2532483A

GB2532483A - Electrode assembly, electrode assembly product, electrode assembly system and method for installing electrode assembly

Info

Publication number: GB2532483A
Application number: GB1420651.0A
Authority: GB
Inventors: John Francis Philip Jones Colin; Lamont-Black John
Original assignee: Electrokinetic Ltd
Current assignee: Electrokinetic Ltd
Priority date: 2014-11-20
Filing date: 2014-11-20
Publication date: 2016-05-25
Anticipated expiration: 2034-11-20
Also published as: GB201706619D0; GB2532483B; GB2546444A; GB2546444B; GB201420651D0

Abstract

An electrode assembly(10, 72), for installation in a substrate (71) for use in electrokinetic treatment of the substrate(71), is described, together with an electrode assembly product and system comprising an electrode assembly and a method of installation. The electrode assembly(10, 72) comprises: a tube(12) for collecting and draining fluid from the substrate(71), said tube(12) having a sidewall comprising openings(14) for allowing fluid to enter the tube (12) from the substrate (71); a filtration membrane (16) surrounding the tube (12), for preventing at least some particulate matter from entering the tube (12) through said openings (14); and a plurality of conducting members (18) surrounding or associated with said filtration membrane (16), the electrode assembly(10, 72) is flexible. A system of electrodes(70) for electro kinetic/osmatic drainage, and a method of installing the electrodes in a curved trench are also claimed.

Description

ELECTRODE ASSEMBLY, ELECTRODE ASSEMBLY PRODUCT, ELECTRODE ASSEMBLY SYSTEM AND METHOD FOR INSTALLING ELECTRODE ASSEMBLY The present invention relates to an electrode assembly, a product and system comprising said electrode assembly, and a method for installing said electrode assembly, and relates particularly, but not exclusively, to a cathode assembly for use in an electrokinetic system for treating a ground substrate.

Electrokinetic processes can be used for ground improvement and reinforcement and slope stabilisation. In particular, electrokinetic treatments can be used to improve the strength of the soil material, reduce pore water pressure, reinforce the soil mass and provide drainage. Anode and cathode electrodes are installed into the ground and connected 15 to a power supply to set up electric fields within the soil mass. This causes water to flow away from the anodes and towards the cathodes, which collect and drain the water from the treated ground. Soft and disturbed soils may experience a large pore water suction resulting in consolidation of the soil and an increase in its cohesion. After completion of the active electrokinetic treatment, the anodes may be completed as soil nails and the cathodes may remain in the ground as drains.

Slope stabilisation is an important application of electrokinetic ground treatments. Unstable embankments and cuttings represent a major problem for railway and highway authorities. In the majority of cases slopes in soils fail or become unstable owing to a number of factors, including weak soils, excessive pore water pressures, over-steepened slopes, and excessive external loadings.

A recurrent issue in ground engineering is a generally large degree of uncertainty about the composition, distribution and engineering characteristics of the materials in the ground. Similarly, variations in groundwater composition, quantity and flow in spatial and temporal dimensions frequently introduces additional complexity and uncertainty in geomechanical, hydraulic, electrokinetic and electrical characteristics. Under such uncertainties it is necessary that any engineering intervention used to improve or stabilise the ground should be inherently adaptable to ground and groundwater conditions that may change and change rapidly with respect to space and or time.

Electrokinetic ground improvement and slope stabilisation, for example using electrokinetic geosynthetic (EKG) materials, is adaptable to a large range of ground conditions. The approach comprises up to four different treatment components, namely: (i) ground improvement by electro-osmosis, (ii) ground strengthening using reinforcement (iii) drainage and, optionally, (iv) soil modification using chemical conditioners.

In the active phase, that is, during the application of the electric field, water is transported by electro-osmosis through the soil mass towards the cathodes. In the treatment of slopes, the cathodes may be installed rising a few degrees above the horizontal in order to encourage drainage of water out of the slope. During the passive phase, that is, after the voltage has been removed from the electrodes, the installed cathodes continue to intercept and drain zones of groundwater.

Electro-osmotic flow of water and the development of increased effective stress is driven by a combination of the electro-osmotic characteristics of the ground and the electric field generated in the ground by the arrangement of the electrodes and the voltages applied to the electrodes. The functions required from anode and cathode electrodes are dissimilar and therefore their structure and deployment are different.

Preferred embodiments of the present invention seek to overcome one or more disadvantages of the prior art.

According to a first aspect of the invention, there is provided an electrode assembly, for installation in a substrate for use in electrokinetic treatment of the substrate, the electrode assembly comprising: a tube for collecting and draining fluid from the 10 substrate, said tube having a sidewall comprising openings for allowing fluid to enter the tube from the substrate; a filtration membrane surrounding the tube, for preventing at least some particulate matter from entering the tube through said openings; and a plurality of conducting members surrounding or associated with said filtration membrane; wherein said electrode assembly is flexible.

Being flexible, the electrode assembly is able to adapt to non-linear alignments in the ground. These may arise as a result of design intention, for example by the employment of directional drilling techniques, which set out with the intention of creating a curved borehole, or an anticipated deviation from linearity during service owing to ground movements caused by consolidation or shear defoimation.

For example, an electrode assembly may be installed in a trench having a rough or uneven profile as a result of obstructions such as boulders. A flexible electrode assembly may accommodate bending and flexing without cracking or fracturing when the trench is backfilled. Flexible electrodes may also bend to accommodate small ground movements without the risk of cracking or rupturing.

Flexible electrode assemblies may be intentionally installed in an intentionally curvilinear arrangement, which may provide various advantages, including improving the uniformity of an electric field, generating an electric field which follows a curved shear surface or failure zone, optimisation of the self-draining function of the cathodes, and improvement of the installation process. For example, this may allow electrodes to be installed in a desired location from a position of relative ease (compared to, for 10 example, slope climbing) and thereby reduce costs.

Using flexible electrode assemblies, long electrodes may be installed as a continuous, non-modular electrode, and may be conveniently transported as a coil or on a reel.

The electrode assembly may be flexible to the extent that at least a portion of the electrode assembly is reconfigurable between a substantially straight configuration and a curved configuration having a radius of curvature substantially equal to or less than 10 metres.

Said curved configuration may have a radius of curvature 20 substantially equal to or less than 5 metres, or substantially equal to or less than 1 metre.

According to a second aspect of the invention, there is provided an electrode assembly, for installation in a substrate for use in electrokinetic treatment of the 25 substrate, the electrode assembly comprising: a tube for collecting and draining fluid from the substrate, said tube having a sidewall comprising openings for allowing fluid to enter the tube from the substrate; a filtration membrane surrounding the tube, for 30 preventing at least some particulate matter from entering the tube through said openings; and a mesh surrounding said filtration membrane, said mesh comprising a plurality of conducting members.

The mesh of conducting members surrounding the filtration membrane reduces the likelihood of puncture or other damage to the filtration membrane, which may result from interaction with roots and sharp stones or other sharp objects in the ground, particularly during the installation process or due to subsequent ground movements. Damage may allow the ingress of silt, which would clog the tube and reduce drainage.

The mesh may comprise at least one metal.

Metals advantageously provide both strength and good electrical conductivity.

The mesh may comprise two or more different metals.

This enables the individual properties of different 15 metals, for example conductivity, corrosion resistance and strength, to be combined. In particular, the metals in the mesh may be selected to achieve both the desired strength and the resistance necessary to avoid unacceptably high voltage drops.

The mesh may comprise copper.

The mesh may comprise stainless steel.

In particular, a blend of copper and stainless steel provides a mesh which is both strong and has high conductivity.

The mesh may be braided.

Braiding gives good mechanical strength, and ensures that the conducting members of the mesh are firmly associated with each other, improving voltage transmission to the distal end of the electrode.

According to a third aspect of the invention, there is provided an electrode assembly, for installation in a substrate for use in electrokinetic treatment of the substrate, the electrode assembly comprising: a tube for collecting and draining fluid from the substrate, said tube having a sidewall comprising openings for allowing fluid to enter the tube from the substrate; a filtration membrane surrounding the tube, for preventing at least some particulate matter from entering the 10 tube through said openings; and a plurality of conducting members associated with said filtration membrane; wherein said filtration membrane extends transversely away from said tube to form an extended collection region comprising two adjacent spaced-apart portions of the filtration membrane, for collecting fluid from the substrate for drainage by the tube.

The extended collection region provided by the electrokinetic filtration membrane provides a larger electrode surface area for driving electro-osmotic flow and a larger filtration surface over which fluid is collected. In use, the extended collection region extends upwardly from the tube, so that fluid entering the collection region moves downwards under gravity to the tube, enters the tube through the openings and then drains along the tube.

The electrode assembly may further comprise a spacer element located between said adjacent spaced-apart portions of the filtration membrane.

The spacer element may hold the two portions of the 30 filtration membrane apart to improve drainage from the space between them to the tube.

The collection region may be substantially planar.

The plurality of conducting members may comprise substantially transversely-oriented conducting members and substantially longitudinally-oriented conducting members.

This arrangement may improve conduction of electric current through the filtration membrane to ensure that all parts of the filtration membrane are able to act as an electrode.

The plurality of conducting members may be substantially 10 evenly spaced in the transverse and/or longitudinal directions.

The electrode assembly may further comprise a plurality of closely-spaced, longitudinally-oriented conducting members at an edge of the filtration membrane distal from the tube.

In use, these conducting members can be used to provide a relatively low-resistance path for conducting electricity to parts of the electrode assembly distant from the power supply so that the voltage drop along the electrode assembly is minimised.

The electrode assembly defined above may further comprise at least one first longitudinal section and at least one second longitudinal section, configured such that, in use, said first longitudinal section is operable for conducting electrical current to or from said substrate independently of said second longitudinal section.

According to a fourth aspect of the invention, there is provided an electrode assembly, for installation in a substrate for use in electrokinetic treatment of the substrate, the electrode assembly comprising: a tube for collecting and draining fluid from the substrate, said tube having a sidewall comprising openings for allowing fluid to enter the tube from the substrate; a filtration membrane surrounding the tube, for 5 preventing at least some particulate matter from entering the tube through said openings; and a plurality of conducting members surrounding or associated with said filtration membrane; wherein the electrode assembly comprises at least one first longitudinal section and at least one second longitudinal section, configured such that, in use, said first longitudinal section is operable for conducting electrical current to or from said substrate independently of said second longitudinal section.

By allowing operation of the first longitudinal section for conducting electrical current to or from said substrate, independently of said second longitudinal section, costs and duration of treatment may be reduced, by selectively targeting the electrokinetic treatment. For example, a voltage may be applied only to sections of the electrode assembly proximal to the slope surface, or to a weak zone of the ground, or another region where electrokinetic ground improvement is particularly beneficial. The passive drainage function of non-electrified sections of the electrode assembly may still be beneficial in other regions where electrokinetic ground improvement is of lower benefit.

In one embodiment, the conducting members in said first longitudinal section are electrically isolated from conducting members in said second longitudinal section.

In another embodiment, the electrode assembly further comprises an insulating layer for insulating conducting members in said second longitudinal section from said substrate.

In another embodiment, said conducting members surround or are associated with said filtration membrane only in said 5 first longitudinal section.

The electrode assembly according to the second, third or fourth aspects of the invention may be flexible.

Said curved configuration may have a radius of curvature substantially equal to or less than 5 metres, or substantially 15 equal to or less than 1 metre.

The electrode assembly according to any of the above aspects of the invention may be a cathode assembly.

The electrode assembly is particularly suited for electrokinetic drainage of water from ground substrates, during which process water drains towards the cathodes. However, the skilled person will appreciate that any of the electrode assemblies described above may be operated as an anode depending on the application.

The substrate may be a ground substrate.

The fluid may comprise water.

The filtration membrane may comprise a geosynthetic material.

The filtration membrane may comprise a geotextile.

The filtration membrane comprises an electrokinetic 30 geosynthetic material.

According to a fifth aspect of the invention, there is provided an electrode assembly product comprising: an electrode assembly according to any of the first to fourth aspects of the invention, wherein said electrode assembly is S arranged as a coil.

A coiled electrode assembly is particularly convenient for transport and installation. This enables long electrodes to be manufactured and transported to site as a single, non-modular electrode, improving manufacturing efficiency, reducing installation time and reducing space requirements at the installation site.

The electrode assembly product may further comprise a reel around which said electrode assembly is wound.

This may improve ease of installation, particularly where 15 access is limited, as the electrode assembly may be gradually unwound as it is installed.

According to a sixth aspect of the invention, there is provided an electrokinetic system, comprising: a plurality of electrodes installed in a substrate for use in electrokinetic treatment of the substrate, the plurality of electrodes comprising at least one first electrode, and at least one second electrode spaced apart from said first electrode; and at least one power supply for applying a potential 25 difference between at least one said first electrode and at least one said second electrode for driving an electrokinetic process within the substrate; wherein at least one said electrode comprises an electrode assembly according to any of the first to fourth 30 aspects of the invention.

At least a portion of at least one said electrode may be substantially curved.

The portion of said at least one said electrode may have a radius of curvature substantially equal to or less than 10 5 metres.

The portion of said at least one said electrode may have a radius of curvature substantially equal to or less than 1 metre.

An electrokinetic system including one or more curved or curvi-linear electrodes may generate electric fields better adapted to the peculiarities of the substrate to be treated, for example to adapt the electric field to a curved shear surfaces, or to improve uniformity of the field generated.

At least one said electrode may comprise an electrode assembly wherein the electrode assembly comprises at least one first longitudinal section and at least one second longitudinal section, configured such that, in use, said first longitudinal section is operable for conducting electrical current to or from said substrate independently of said second longitudinal section, wherein conducting members in said first longitudinal section are electrically-connected to at least one said power supply, and wherein conducting members in said second longitudinal section are not electrically-connected to a power supply.

This allows electrokinetic treatment to be targeted at the zones where it is most beneficial, while allowing passive drainage at other zones, resulting in a reduction in costs.

According to a seventh aspect of the invention, there is provided a method for installing an electrode assembly in a 30 substrate, for use in electrokinetic treatment of the substrate, the method comprising: providing an electrode assembly; forming a trench or borehole; and inserting said electrode assembly into said trench or borehole; wherein said trench or borehole is substantially curved.

At least a portion of the trench or borehole may have a radius of curvature substantially equal to or less than 10 metres.

At least a portion of the trench or borehole may have a radius of curvature substantially equal to or less than 5 10 metres.

The electrode assembly may be provided as a coil; said method further comprising the step of unwinding the electrode assembly from the coil as it is fed into the trench or borehole.

The electrode assembly may comprise an electrode assembly according to any of the first to fourth aspects of the invention.

A preferred embodiment of the present invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings, in which: Figure 1 shows an armoured electrode assembly according to an embodiment of the present invention; Figure 2 shows an electrode assembly according to another embodiment of the invention; Figure 3 schematically illustrates an electrokinetic system according to a further embodiment of the invention; Figure 4 schematically illustrates another electrokinetic system according to a further embodiment of the invention; Figure 5 schematically illustrates another electrokinetic system according to a further embodiment of the invention; Figure 6 schematically illustrates another electrokinetic system according to a further embodiment of the invention; Figure 7 schematically illustrates another electrokinetic system according to a further embodiment of the invention; and Figure 8 schematically illustrates another electrokinetic 10 system according to a further embodiment of the invention.

A first embodiment of an electrode assembly 10 according to the present invention is shown in Figure 1, in the form of a cathode assembly 10 for installation in a ground substrate for use in electrokinetic treatment of the ground. In electrokinetic ground treatment, a cathode has two primary functions. Firstly, it acts as a negatively charged electrode and thus collects current from the ground and conducts it to the surface where it is connected via a cable array to a power supply. Secondly, it collects water from the ground and conducts it to the surface and thus out of the ground.

Referring to Figure 1, the electrode assembly 10 comprises a tube 12 for collecting and draining water from the ground. The tube 12 has openings 14 along the length of its sidewall, through which fluid from the substrate can enter the tube 12. The openings 14 may be holes or slots, formed for example by perforating the sidewall. Alternatively, the sidewall of the tube 12 may have a mesh or grid-like structure. Cathodes are generally installed rising a few degrees above the horizontal so that any water entering the 30 tube 12 can drain along the tube and out of the ground. The materials and size of the tube may be selected according to the application. In one example, the tube 12 is a plastic tube approximately 50 -60mm in diameter. The tube 12 may be rigid or flexible. The size of the holes or openings 14 in the tube 12 may, for example, be in the range of 0.5 to 8 millimetres.

A filtration membrane 16 surrounds the tube 12, for preventing at least some particulate matter, i.e. fine grained material, from entering the tube 12 through the openings 14 and potentially clogging the drainage tube 12. The filtration membrane 16 is selected by air permeability and pore size to be most appropriate for the particle size distribution of the substrate in which it is to be installed. Suitable materials for the filtration membrane 16 include geosynthetic materials such as geotextiles, for example woven or non-woven polymeric fabrics such as polyester, polypropylene polyamide, polyacrylamide and nylon etc. The pore size associated with the filtration membrane 16 may range from approximately 50 micrometres to approximately 500 micrometres.

A metallic mesh 18 surrounds the filtration membrane 16. In use, the mesh 18 is connected to a power supply so that the electrode assembly acts as a cathode. The conducting mesh 18 has a sufficiently low electrical resistance to conduct the anticipated current to the distal end of the cathode (i.e. the end deepest in the ground or furthest from the connection to the power supply) without suffering large voltage drops. This becomes particularly important if the cathodes is long, for example in excess of 12m. Furthermore, the cathode needs to resist diametrical crushing, tear or puncture damage to filtration membrane 16 due to roots, sharp stones or other sharp objects in the ground. This is particularly likely during the installation process. It has been found that a conductive mesh 18 can provide the necessary conductivity while offering sufficient protection to the filtration membrane 16. The electrode assembly may be referred to as an armoured' electrode assembly due to the protection provided by the metallic mesh 18. In this embodiment, the mesh 18 is a braided metallic mesh. Braiding ensures good contact between the multiple conducting members of the mesh 18, thereby ensuring good electrical conductivity along the length of the electrode assembly 10, even Metallic conducting members if it suffers minor damage. may provide good strength, flexibility and electrical conductivity. The mesh 18 may comprise stainless steel, copper, mild steel, aluminium or 10 other electrically conductive material. The number, density, compositional blend and diameter of the metals or other materials in the mesh 18 are selected to achieve the resistance necessary to avoid unacceptably high voltage drops along the length of the electrode 10. For example, the mesh 18 may be formed from a blend of two different metals, for example stainless steel and tinned copper or other conductive fibre, to provide the desired conductivity. The mesh 18 may be configured as a woven, braided or welded structure. As an example, the diameter of the wires of the mesh 18 may have diameters in the range from approximately 0.1 millimetres to approximately 0.7 millimetres. The mesh 18 may be configured with a square, hexagonal, rhomboidal or other polygonal pattern, with a characteristic spacing between the wires being in the range 0.2 to 10 millimetres. The mesh 18 may be flexible, enabling the electrode assembly 10 to be formed rigid or flexible, depending also on the composition and structure of material used for the drainage tube 12.

With reference to Figure 2, an embodiment of an electrode assembly 20 for use in electrokinetic treatment of a substrate, according to another embodiment of the invention comprises a tube 22 for collecting and draining fluid from the substrate, a filtration membrane 24, and a plurality of conducting members 26, 28 associated with said filtration membrane 24. As in the previous embodiment, the tube 22 comprises openings (not visible in Figure 2) for allowing fluid to enter the tube 22 from the substrate, and the filtration membrane 24 surrounds the tube 22 to prevent fine-grained particulate matter from entering the tube through the openings, to prevent clogging of the tube 22.

The conducting members 26, 28 include transverse conductors 26 and longitudinal conductors 28, distributed throughout the filtration membrane 24, for collecting electrical current from the substrate and transmitting it through the filtration membrane 24 to a power supply. The filtration membrane 24 may comprise a geosynthetic material, in particular an electrokinetic geosynthetic material or textile. The conducting members 26, 28 may be woven, sewn or otherwise integrated into the fabric of the filtration membrane 24. As an example, the conducting members 26, 28 may be wires having diameters in the range from approximately 0.1 millimetres to approximately 0.7 millimetres, spaced apart by around 0.2 to 10 millimetres.

The filtration membrane 24 extends transversely away from the tube 22 to form an extended collection region 30 comprising two adjacent portions of the filtration membrane 24, which are held apart by an internal spacer 32, and the space between them. In use, the extended collection region or drainage fin' 30 extends substantially vertically upwards above the drainage tube 22. Water collected in the drainage fin 30 is conducted vertically downwards under gravity and enters the tube 22 for drainage out of the substrate. To connect the transverse and longitudinal conductors 26, 28 to a power supply, a plurality of closely-spaced, longitudinally-oriented conducting members 34 are provided at the edge of the filtration membrane 24, at the upper edge of the drainage fin 30. These conducting members 34 form a conductive strip which ensures good electrical connection between the power supply connector 36 and all of the transverse conductors 26, to minimise any voltage drop along the longitudinal length of the electrode assembly. 20. The 'drainage fin' 30 may extend up to around 3 metres or so from the drainage tube 22. The The electrode assemblies 10, 20 shown in Figures 1 and 2 respectively may be flexible. Flexible electrodes offer additional advantages in that they are able to be installed along curved paths, for example to adapt the shape of electric field produced by the electrodes to the shape of a shear Directional drilling intentionally curved adapt during service surface (failure surface) in the ground. techniques may be used to create an borehole. Flexible electrodes to ground movements caused deformation. The curvature may by of also consolidation or shear a borehole formed by directional drilling techniques may be limited to a radius of curvature length of insertion of around 10 the borehole.

metres, depending on the site and A flexible electrode is required for borehole. However, the flexible to adapt to more for example due to deformations Or a sharp change in direction into such a curved electrodes may be sufficiently abrupt changes in direction, or movements in the ground, where a borehole meets the surface. For example, the electrode assemblies may be sufficiently flexible to adapt to a radius of curvature of around 1 metre or less.

Another convenience of flexible electrode assemblies is that they may be provided as a product in a coiled form. This saves space and makes transport of the electrode assemblies more straightforward. In addition, it enables the electrode assembly to be installed on site from a coil or reel. This can be useful for installing long electrodes, particularly where access is difficult, since these might otherwise need to be installed in sections which would then need to be electrically and mechanically connected to each other. In electokinetic installations, a typical length of the cathodes is in the range 1.5 to 15 metres, but cathodes longer than 20 metres have been installed at some sites and it is likely that some applications will require significantly longer cathodes. 5 By providing a flexible electrode assembly wound in a coil or on a reel, the electrode assembly can be unwound from the coil or reel as it is fed into the trench or borehole, saving space at the installation site. The inner portion of the coil, or the core of a reel on which the coil is wound, may typically 10 have a diameter from around 20 centimetres up to around 2 metres. This requires sufficient flexibility that the electrode assembly can be curved to a radius of curvature of around 1 metre or less.

Examples of installed electrokinetic systems incorporating flexible cathodes are illustrated in Figures 3 to 7.

Figure 3 shows an electrokinetic system 40 comprising a plurality of electrodes 42, 48 installed in a substrate 41, in the form of a slope 41, for use in electrokinetic treatment of the substrate 41. The electrodes 42, 48 comprise multiple first electrodes 42 and multiple second electrodes 48 spaced apart from said first electrodes 42. Here, the first electrodes 42 are cathodes and the second electrodes 48 are anodes. The electrokinetic system 40 also comprises one or more power supplies and associated cables (not shown) for applying a potential difference between the anodes 48 and cathodes 42 for driving an electrokinetic process within the substrate 41.

In this embodiment, the cathodes 42 are formed using 30 flexible cathode assemblies 10 as described above with reference to Figure 1. The cathodes 42 are installed in trenches 46 or slits formed using, for example, a narrow bucket excavator, a drag line or mole plough. The trenches 46 may have a rough or uneven profile as a result of obstructions e.g. boulders. A flexible cathode 42 is placed in the bottom of a respective trench 46, thereby taking on a curved or curvilinear profile according to the profile of the bottom of the trench 42. The trenches 46 and cathodes 42 are also curved at the base of the installation so that the lower ends 42a of the cathodes return to the surface of the slope 41. This allows water collected in the drainage tubes 12 of the cathode assemblies 10 to drain out of the slope 41.

The cathodes 42 are then surrounded with a porous particulate material which is selected to have a suitable particle size distribution for retaining water within its pore spaces for transmission of the electric field between the anodes 48 and the cathodes 42. The flexible cathodes 42 are able to accommodate bending and flexing without cracking or fracturing when the trenches 46 are backfilled, either with the originally excavated material or granular drainage material such as clean gravel. The mesh 18 of the cathode assemblies 10 of the cathodes 42 prevent damage to the 20 filtration membrane 16 during installation or subsequent ground movements.

In the embodiment shown in Figure 3, the anodes 48 are installed substantially orthogonal to the cathodes 42. The ends 48a of the anodes 48 are accessible at the surface of the 25 slope 41 to allow connection to a power supply.

Figure 4 shows another electrokinetic system 50 comprising a plurality of electrodes 52, 58 installed in a substrate 51, in the form of a slope 51, for use in electrokinetic treatment of the substrate 51. As in the previous embodiment, the electrodes 52, 58 comprise multiple cathodes 52 and anodes 58 spaced apart from each other and connected to one or more power supplies (not shown).

In this embodiment, the cathodes 52 are formed using flexible cathode assemblies 20 as described above with reference to Figure 2. As in the previous embodiment, the cathodes 52 are installed in trenches 56, and their 5 flexibility allows them to adapt to the profile of the trenches 56. In particular, the upper portions of the cathodes 52 are substantially parallel to the slope 52, but the cathodes 52 are bent or curved close to the base of the slope 51 so that the lower ends 52a of the cathodes 52 emerge at the base of the slope 51. The anodes 58 are installed substantially orthogonal to the slope 51, with their ends 58a accessible at the surface of the slope 51. The extended collection region or drainage fin 54, 30 of each cathode assembly 52, 20 extends upward from the drainage tube 52, 22 so that water collected in the drainage fin 54, 30 is conducted downward to the tube 52, 22 for draining out of the ground 51.

Figure 5 shows a further electrokinetic system 60 comprising a plurality of electrodes 62, 68 installed in a 20 substrate 61, in the form of a slope 61, for use in electrokinetic treatment of the substrate 61. As in the previous embodiments, the electrodes 62, 68 comprise multiple cathodes 62 and anodes 68 spaced apart from each other and connected to one or more power supplies (not shown). The cathodes 62 are formed using flexible cathode assemblies, for example the flexible cathode assemblies 10, 20 as described above with reference to Figures 1 and 2.

In this embodiment, the flexible cathodes 62 are installed in boreholes, formed by drilling into the slope 61 from the surface of the slope 61. The boreholes are drilled into the slope 61 rising a few degrees above horizontal so that water collected by the cathodes 62 drains towards the surface of the slope 61. The proximal ends 62a of the cathodes 62 emerge at the surface of the slope 61 to allow the water to drain out of the ground and to allow electrical connection of the cathodes 62 to the power supply. As in the previous embodiments, the anodes 58 are installed substantially orthogonal to the slope 51, with their ends 58a accessible at the surface of the slope 51 for connection to the power supply.

The slope 61 illustrated in Figure 5 has a circularly shaped failure indicated by shear surface 66. Relative 10 movement of the ground on each side of the shear surface 66 has caused a step in the profile of the cathodes 62 at the location of the shear surface 66. The flexibility of the cathodes 62 permits the accommodation of small ground movements in this manner without the risk of cracking or rupturing. Indeed, such movement is anticipated due to consolidation and volume change of the ground due to the electrokinetic treatment. Moreover, such movement is required by the combined treatment, in order that the anodes may take up the desired restraining load as part of their long-term passive reinforcement function.

Figure 6 illustrates a further electrokinetic system 70 in which directional drilling is used to install the cathodes 72 parallel to a curved shear surface 76 in a sloping ground substrate 71. Directional drilling can be used to create boreholes which are intentionally curved or curvilinear. The anodes 78 are installed substantially orthogonal to the surface of the slope 71 as in the previous embodiments. This technique can be used to tailor the shape of the electric field created by the electrodes 72, 78 to specific alignments in the ground to be treated.

As can be seen from Figure 6, directional drilling also enables electrodes to be installed from flat ground above the slope 71, which is often much more accessible for equipment and personnel than drilling on the slope itself and therefore reduce costs. The upper ends 72b of the cathodes 72 are accessible above the slope 71, and the lower ends 72a of the cathodes 72 emerge at various points down the surface of the slope 71 for drainage.

Figure 7 illustrates another electrokinetic system 80, similar to that shown in Figure 6, in which directional drilling is used to install cathodes 82 parallel to a curved shear surface 86 in a sloping ground substrate 81. The anodes 88 are installed substantially orthogonal to the surface of the slope 81 as in the previous embodiments.

In this embodiment, access to the slope 81 is particularly difficult due to the presence of a cliff 83 at the foot of the slope 81. It is particularly beneficial in this situation to install the cathodes 82 from the flat ground above the slope 81. The upper ends 82b of the cathodes 82 are therefore accessible above the slope 81. The curved cathodes 82 are drilled into the bedrock beneath the sediments which are failing, such that the lower ends 82a of the cathodes 82 emerge in the cliff surface 83 below the slope 81 for draining water collected by the cathodes 82.

Figure 8 illustrates a further electrokinetic system 90 comprising a plurality of electrodes 92, 98 installed in a substrate 91, in the form of a slope 91, for use in electrokinetic treatment of the substrate 91. As in the embodiment described above with reference to Figure 5, the electrodes 92, 98 comprise multiple cathodes 92 and anodes 98 spaced apart from each other and connected to one or more power supplies (not shown). The cathodes 92 may formed using rigid or flexible cathode assemblies, for example the cathode assemblies 10, 20 as described above with reference to Figures 1 and 2, and are installed in boreholes formed by drilling into the slope 91 from the surface of the slope 91. The proximal ends 92a of the cathodes 92 emerge at the surface of the slope 91 to allow the water to drain out of the ground and to allow electrical connection of the cathodes 92 to the power supply. The anodes 98 are installed substantially orthogonal to the slope 91, with their ends 98a accessible at the surface of the slope 91 for connection to the power supply.

The slope 91 illustrated in Figure 8 has a circularly-shaped failure indicated by shear surface 96. Electrokinetic treatment of the ground 91 in the region 100 proximal the shear surface 96 and the surface of the slope 91 may be highly beneficial. In some circumstances, drainage of the ground 91 in the region 102 further (or deeper) from the surface of the slope 91 may still be advantageous, but ground improvement by electrokinetic treatment may be of lower value.

The cathode drains 92 shown in Figure 8 have been adapted to target electrokinetic treatment in the region 100 proximal the shear surface 96, while allowing passive drainage in the region 102 further from the surface of the slope 91. The cathodes 92 comprise a first longitudinal section 92c and a second longitudinal section 92d, configured such that, in use, said first longitudinal section 92c is operable for conducting electrical current to or from the substrate 91 independently of the second longitudinal section 92d. The sections 92c of the cathodes 92 proximal to the surface of the slope 91 are electrically-connected to a power supply so as to act as an electrode, i.e. without the application of a voltage. The sections 92d of the cathodes 92 distal from the surface of the slope 91 are not electrically-connected to a power supply so act as passive drains, i.e. without the application of a voltage. By targeting the electrokinetic treatment of the ground 91 in this way, power consumption may be reduced, leading to lower costs, and/or a shorter electrokinetic treatment phase. Further costs savings may be made due to the lower rating required for the cabling between the electrodes 92, 98 and the power supply.

Although this concept of targeted treatment is illustrated using straight cathodes 92, which may be rigid or 5 flexible, it is equally applicable to curved cathodes 92.

Electrical isolation between the first and second longitudinal sections of the cathodes 92 may be achieved in several ways.

In one embodiment, the conducting members 18, 26, 28 surrounding or associated with the filtration membrane 16, 24 in the first longitudinal section 92c of the cathode 92 are electrically isolated from those in the second longitudinal section 92d of the cathodes 92. This may be achieved by a break in the conducting members (e.g. by a break in the mesh 18 shown in Figure 1, or a break in the longitudinal conducting members 28 and conductive strip 34 shown in Figure 2). The conducting members 18, 26, 28 in each section 92c, 92d of the cathode 92 may be independently powered, for example they may each be operated at different voltages, or those in one section may be disconnected from the power supply to be completely passive.

In another embodiment, the cathodes 92 comprise an insulating layer surrounding the second longitudinal section 92d of the cathode 92, preventing electrical current from flowing from the substrate to the cathode 92 in the region 102 in which the second longitudinal section 92d of the cathode 92 is located.

In another embodiment, the second longitudinal section 92d of the cathode may be formed without any conducting 30 members surrounding or associated with the filtration membrane 16, 24. Nonetheless, the drainage tube 12, 22 and filtration membrane 16, 24 may be continuous between the first and second longitudinal sections 92c, 92d.

In all three embodiments, the first and second longitudinal sections 92c, 92d may be formed as separate 5 cathode assemblies, and connected together by means of couplers (not shown) which provide mechanical connection between the first and second longitudinal sections 92c, 92d. The couplers enable fluid to flow continuously between the tubes of the first and second longitudinal sections 92c, 92d, 10 but prevent ingress of fine particulate matter into the tube between the filtration membranes of the two adjoining sections. The couplers may connect adjoining sections by means of a screw thread.

The couplers may be configured to provide either 15 electrical isolation or electrical connection between the first and second longitudinal sections 92c, 92d. By electrically isolating the first and second longitudinal sections 92c, 92d, they may be independently powered.

The couplers described above may also be used for connecting identical or dissimilar cathode assemblies to create a long cathode powered from a single power supply. This may be useful for maintaining mechanical integrity, for the purposes of ease of installation and preventing fine particulate matter entering the tube by bypassing the filter, while maintaining electrical continuity along the length of the cathode. In such applications, the couplers would be configured to provide electrical connection between the coupled sections.

Although the above embodiments have been described in 30 terms of cathode assemblies for use as cathodes in electrokinetic systems, it will be appreciated that the described electrode assemblies may also be used as anodes.

Applications of the electrode assemblies for electrokinetic treatment of slopes, namely slope stabilisation, have been described. However, the skilled person will appreciate the applicability of the above 5 described electrode assemblies and installation techniques to horizontal ground.

The skilled person will appreciate that the features of the above-described electrode assemblies may be combined in various combinations.

It will also be appreciated that the above-described electrode assemblies may be operated as either cathodes or anodes depending on the nature of the material to be dewatered and the result to be achieved.

It will be appreciated by persons skilled in the art that the above embodiments have been described by way of example only, and not in any limitative sense, and that various alterations and modifications are possible without departure from the scope of the invention as defined by the appended claims.

Claims

CLAIMS1. An electrode assembly, for installation in a substrate for use in electrokinetic treatment of the substrate, the electrode assembly comprising: a tube for collecting and draining fluid from the substrate, said tube having a sidewall comprising openings for allowing fluid to enter the tube from the substrate; a filtration membrane surrounding the tube, for preventing at least some particulate matter from entering the 10 tube through said openings; and a plurality of conducting members surrounding or associated with said filtration membrane; wherein said electrode assembly is flexible.
2. An electrode assembly, for installation in a substrate for use in electrokinetic treatment of the substrate, the electrode assembly comprising: a tube for collecting and draining fluid from the substrate, said tube having a sidewall comprising openings for allowing fluid to enter the tube from the substrate; a filtration membrane surrounding the tube, for preventing at least some particulate matter from entering the tube through said openings; and a mesh surrounding said filtration membrane, said mesh comprising a plurality of conducting members.
3. An electrode assembly according to claim 2, wherein said mesh comprises at least one metal.
4. An electrode assembly according to claim 3, wherein said mesh comprises two or more different metals.
5. An electrode assembly according any of claims 2 to 4, wherein said mesh comprises copper.
6. An electrode assembly according any of claims 2 to 5, wherein said mesh comprises stainless steel.
7. An electrode assembly according any of claims 2 to 6, wherein said mesh comprises stainless steel and copper.
8. An electrode assembly according to any of claims 2 to 7, wherein said mesh is braided.
9. An electrode assembly, for installation in a substrate for use in electrokinetic treatment of the substrate, the electrode assembly comprising: a tube for collecting and draining fluid from the substrate, said tube having a sidewall comprising openings for allowing fluid to enter the tube from the substrate; a filtration membrane surrounding the tube, for preventing at least some particulate matter from entering the tube through said openings; and a plurality of conducting members associated with said filtration membrane; wherein said filtration membrane extends transversely away from said tube to form comprising filtration for drainage by the tube.an extended collection region portions of the from the substrate two adjacent spaced-apart membrane, for collecting fluid
10. An electrode assembly according to claim 9, further comprising a spacer element located between said adjacent spaced-apart portions of the filtration membrane.
11. An electrode assembly according to claim 9 or 10, wherein said plurality of conducting members comprises substantially transversely-oriented conducting members and substantially longitudinally-oriented conducting members.
12. An electrode assembly according to any of claims 9 to 11, wherein said plurality of conducting members are substantially 5 evenly spaced in the transverse and/or longitudinal directions.
13. An electrode assembly according to any of claims 9 to 12, further comprising a plurality of closely-spaced, longitudinally-oriented conducting members at an edge of the 10 filtration membrane distal from the tube.
14. An electrode assembly according to any one of claims 2 to 13, wherein the electrode assembly comprises at least one first longitudinal section and at least one second longitudinal section, configured such that, in use, said first longitudinal section is operable for conducting electrical current to or from said substrate independently of said second longitudinal section.
15. An electrode assembly, for installation in a substrate for use in electrokinetic treatment of the substrate, the 20 electrode assembly comprising: a tube for collecting and draining fluid from the substrate, said tube having a sidewall comprising openings for allowing fluid to enter the tube from the substrate; a filtration membrane surrounding the tube, for 25 preventing at least some particulate matter from entering the tube through said openings; and a plurality of conducting members surrounding or associated with said filtration membrane; wherein the electrode assembly comprises at least one 30 first longitudinal section and at least one second longitudinal section, configured such that, in use, said first longitudinal section is operable for conducting electrical current to or from said substrate independently of said second longitudinal section.
16. An electrode assembly according to claim 14 or claim 15, 5 wherein conducting members in said first longitudinal section are electrically isolated from conducting members in said second longitudinal section.
17. An electrode assembly according to claim 14 or claim 15, further comprising an insulating layer for insulating 10 conducting members in said second longitudinal section from said substrate.
18. An electrode assembly according to claim 14 or claim 15, wherein said conducting members surround or are associated with said filtration membrane only in said first longitudinal 15 section.
19. An electrode assembly according to any of claims 2 to 18, wherein said electrode assembly is flexible.
20. An electrode assembly according to claim 1 or claim 19, wherein said electrode assembly is flexible to the extent that at least a portion of the electrode assembly may be reconfigured between a substantially straight configuration and a curved configuration having a radius of curvature substantially equal to or less than 10 metres.
21. An electrode assembly according any of the preceding 25 claims, wherein said electrode assembly is a cathode assembly.
22. An electrode assembly according any of the preceding claims, wherein said substrate is a ground substrate.
23. An electrode assembly according any of the preceding claims, wherein said fluid comprises water.
24. An electrode assembly according any of the preceding claims, wherein said filtration membrane comprises a geosynthetic material.
25. An electrode assembly according any of the preceding 5 claims, wherein said filtration membrane comprises a geotextile.
26. An electrode assembly according to any of the preceding claims, wherein said filtration membrane comprises an electrokinetic geosynthetic material.
27. An electrode assembly product comprising: an electrode assembly according any of the preceding claims, wherein said electrode assembly is arranged as a coil.
28. An electrode assembly product according to claim 24, further comprising a reel around which said electrode assembly 15 is wound.
29. An electrokinetic system, comprising: a plurality of electrodes installed in a substrate for use in electrokinetic treatment of the substrate, the plurality of electrodes comprising at least one first electrode, and at least one second electrode spaced apart from said first electrode; and at least one power supply for applying a potential difference between at least one said first electrode and at least one said second electrode for driving an electrokinetic 25 process within the substrate; wherein at least one said electrode comprises an electrode assembly according to any of claims 1 to 23.
30. An electrokinetic system according to claim 29, wherein at least a portion of at least one said electrode is 30 substantially curved.
31. An electrokinetic system according to claim 30, wherein said portion of said at least one said electrode has a radius of curvature substantially equal to or less than 10 metres.
32. An electrokinetic system according to claim 31, wherein 5 said portion of said at least one said electrode has a radius of curvature substantially equal to or less than 1 metre.
33. An electrokinetic system according to any one of claims 29 to 32, wherein at least one said electrode comprises an electrode assembly according to any of claims 9 to 13, wherein 10 said collection region extends upwards from said tube.
34. An electrokinetic system according to any of claims 29 to 33, wherein at least one said electrode comprises an electrode assembly according to claim 16 or claim 17, wherein said conducting members of said first longitudinal section are electrically-connected to at least one said power supply, and wherein said conducting members of said second longitudinal section are not electrically-connected to a power supply.
35. A method for installing an electrode assembly in a substrate, for use in electrokinetic treatment of the 20 substrate, the method comprising: providing an electrode assembly; forming a trench or borehole; and inserting said electrode assembly into said trench or borehole; wherein said trench or borehole is substantially curved.
36. A method according to claim 35, wherein at least a portion of said trench or borehole has a radius of curvature substantially equal to or less than 10 metres.
37. A method according to claim 35, wherein said electrode assembly is provided as a coil; and said method comprises the step of unwinding the electrode assembly from the coil as it is fed into the trench or 5 borehole.
38. A method according to any of claims 35 to 37, wherein said electrode assembly is an electrode assembly according to any of claims 1 to 26.
39. An electrode assembly substantially as described herein 10 with reference to the accompanying drawings.
40. An electrode assembly product substantially as described herein.
41. An electrokinetic system substantially as described herein with reference to the accompanying drawings.
42. A method for installing an electrode assembly in a substrate, for use in electrokinetic treatment of the substrate, substantially as described herein.