Overview

EKG Embankment Construction

EKG Soil Nails and Horizontal Drains

EKG Counterfort Drains

EKG Geochemical Soil Improvement

Environmental Sustainability

 

 

EKG soil nails and horizontal drains

Electrokinetic ground improvement and reinforcement with active and passive drainage improves the strength of the soil material, reinforces the soil mass and provides drainage for the active electrokinetic phase and the passive long term drainage phase. EKG treatment:

• improves soil material strength

• reinforces soil mass

• reduces porewater pressures

 

EKG slope stabilisation electrodes are installed into the slope and connected to a DC controllable power supply to set up a time-varying electric field within the soil mass. Over a period of 6 to 8 weeks this causes water to flow towards the cathode areas and drain from the slope. Concomitantly soft and disturbed soils experience a large porewater suction which results in consolidation of the soil and an increase in its cohesion.


Cutaway illustration showing the installation of electrodes in a slope stabilisation project

After the completion of the active treatment the anodes are completed as soil nails and the cathodes remain in the slope as horizontal drains.

 

 

The sequence of EKG soil nailing

Installation

 

Active Treatment

 

Grout

 

Reinforcement

 

Soil nail reinforcement

By choosing the appropriate combination of anodes and cathodes and a specific electrode array or style of installation, electrokinetic treatment can provide significant long-term benefits in terms of reinforcement and cementation.

After the electrokinetic treatment is complete, the anodes can remain in situ as bonded soil nails, with a design life of up to 120 years. The effect of the soil nail array is to further increase the factor of safety of the slope.

The electrodes achieve an enhanced bond with the soil owing to an improvement in the shear strength of soil, consolidation of the material, reduced plasticity owing to cation exchange and cementation of the nail / soil contact.

If the anodes are chosen and operated with a partially sacrificial function they will produce several distinct effects:

• Dissolved ions in solution will cement the clay around the anode thus stiffening the clay itself forming a ‘mini pile’

• A very strong bond will be created between the soil and the anode

• Additionally if required, the anodes can be conditioned with various ionic solutions e.g. dissolved calcium to foster cation exchange and further improve the soil.

 

The bond strength between the active electrokinetic nail and soil is typically between 2 – 6 times greater than the bond strength achieved by equivalent non-activated nails.

Electrodes can be installed to accommodate the dominant failure mode and can also be orientated to maximize drainage from wet areas in the slope.

EKG horizontal drains

EKG electrodes are designed to function as filtration drainage elements. These can be installed in sympathy with the electrokinetic treatment in such a way as to provide long term passive drainage after completion of the active electrokinetic treatment phase. With this function in mind, the electrodes include these essential features:

• Strong cross section to resist collapse damage

• Geosynthetic filter to prevent clogging with fines

• Open cross section to permit maintenance if necessary

• Drainage design life maximised by

• Strength

• Filtration

 

The provision of long term passive drainage is of important potential use in slopes which have the capacity for water bearing layers of sands and gravels and fissured clays.

Design of EKG treatment

EKG treatment is applicable to at risk or actively failing slopes with combinations of:

• Embankments / cuttings

• Weak fine grained soils (including heterogeneous mixtures e.g. poorly engineered fill)

• Plastic / creep susceptible soils

• Over-steeped slopes

• Poorly draining slopes

• Granular horizons / perched water

 

There are four components to the design:

1. Ground improvement by electroosmosis

2. Reinforcement by soil nailing

3. Reduction in pore pressures by horizontal drainage

4. Ground improvement by soil modification

Of these the most well defined codes of practice for slope stabilisation relate to reinforcement by soil nailing. Design soil nail reinforcement is specifically excluded from Eurocode 7 and therefore we adopt BS8006 as the kernel of the design. Electroosmosis , horizontal drainage and soil modification factors are analysed and designed with using BS8006.

 

EKG electrodes are made to high standard of corrosion protection:

• Design is based on BS8006, HA 68/94, CIRIA C637

• Corrosion protection (TRRL RR380 / HA 68/94, Eurocode 7, Geoguide 7) triple protection possible
- Sacrificial steel (outer anode tube)
- Cement grout
- Galvanising / plastic coating (optional)

• Design life up to 120 yrs

An example installation of the EKG system of multifunctional anodes and cathodes is given in the downloads page.


Illustration of the electrode pattern, wired up for electrokinetic activation

EKG technology has been used to successfully stabilise a failing clay embankment in London resulting in a 26% cost reduction and a 47% reduction in carbon dioxide emissions over conventional methods. The treatment also offered the provision of long term drainage of the slope after successful stabilisation. Complete details of this scheme are documented on the Case Studies page.
System components

System adaptability

The multi-component nature of the EKG approach enables the treatment to be adapted to suit geotechnical settings with significant geological, geomorphological and hydrogeological heterogeneities.

Using a combination of different system components, these effects can be configured to match the specific requirements of the project.

By adjusting the three working parameters of treatment time, voltage, and electrode spacing, different factors can take priority. For example, if treatment time is critical then the use of closer electrode spacing is appropriate. On the other hand, if cost is the main driver a wider spacing of electrodes can be used to reduce the number of electrodes and spread the treatment out over a longer duration.

System sustainability and safety

The EKG system has several advantages in respect of sustainability and safety:

• It requires only small construction plant thus it can gain easy access to most sites

• Once the electrodes are installed there is little visible activity on site

• Electrodes installations, connections and reinforcement can be completed generally without needing to work next to the traffic lane

• It requires no removal of topsoil, this preserves root balls and seed banks and minimises the disturbance to habitats. The system has been used on an endangered species site in Kent.

• It can be undertaken leaving trees in situ

• It has a carbon footprint which is 40% lower than equivalent soil nailing techniques

System cost

The EKG system is competitively priced and owing to some of the above factors, it is generally lower cost than competing systems such as conventional soil nailing or slope slackening.

Conclusions

• Electroosmosis is accepted as an effective physical process

• EKG treatment provides a multi-component treatment approach which is adaptable to variable ground conditions

• Each component of treatment can be used for design based on appropriate laboratory testing results

• Changes in shear strength, drainage conditions and the introduction of reinforcement permits stability analysis with respect to different treatment components

• Field trial has demonstrated technical effectiveness and significant economic, environmental and logistical benefits

• A design framework has been developed
In addition to the structural benefits, EKG combines electroosmosis with accepted engineering methods to deliver slope treatment and construction which has a:

• Low carbon footprint

• Low access requirement

• Low cost

   
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