EKG Remediation of Embankment

Forest of Dean slope stabilisation

Low Impact Benefits

Highway Embankment Stabilisation

Sewage Sludge

Mine Tailings

Railway Embankment Stabilisation

Reinforced Soil

Lagoon Consolidation

Consolidation of Soft Soil

 

constructing a Reinforced Soil wall

The objective of the trial was to build a reinforced soil wall constructed with super soft clay fill. In this application the EKG materials acted both as drainage paths and reinforcement.

Most codes of practice do not permit the use of cohesive soils in the construction of reinforced soil due to potential problems of short term stability and its influence on the durability of metallic reinforcement. The 2012 draft of BS8006 allows thus use of sub-standard fill provided that it can be demonstrated that the material can be improved as part of the construction works and electrokinetic ground improvement is stated as an option.

Short term stability results from low shear strength and poor bond between the reinforcement and the cohesive soil which is aggravated by the development of positive pore water pressures at the soil/reinforcement interface. To illustrate the power of EKG to permit the use of material usually considered to be totally unsuitable, a reinforced-soil wall was constructed with fill in the form of a clay slurry (defined as a disturbed cohesive soil with a water content higher than the liquid limit).

The design established the voltage to be applied and current expected and the length of treatment time required in removing the appropriate amount of water to improve the shear strength of the clay to 20kPa. On this basis it was determined that the required moisture content of the fill was 42% compared to the initial level of 75%. As shown in the Figure below.

The wall was constructed using a 'wraparound' design, utilising sandbags for the front face to temporarily retain the liquid fill. The ends of the trial wall were retained using conventional reinforced soil blocks, and the wall was raised using a staged construction technique. Clay slurry was prepared in a pit adjacent to the wall (photos below) and poured in 300mm layers (cross section shown below). Each lift was constructed and dewatered vertically by electro-osmosis applied via horizontally placed EKG electrodes. Once a lift had been successfully treated then the next lift was constructed, the original cathode now becoming the anode, and the original anode reverting to a reinforcing role.

Construction of a reinforced soil embankment using EKG - showing the pour, the site and the mix

Schematic cross section through the reinforced wall showing the position of EKG with arrows indicating the direction of electroosmotic flow.

The electrokinetically treated zones of the wall showed increased improvement of shear strength (measured by shear vane at 0.25 and 0.5m depth) over untreated areas, especially in zones where electrode spacing was lower (i.e. higher voltage gradient). With successive lifts further improvement took place in underlying lifts due to surcharge loading and drainage through the electrically inactive EKG elements and drains.

These results demonstrate that electrokinetic techniques implemented with EKG can be used to construct reinforced cohesive soil. They have also demonstrated that the electrode spacing and applied voltage gradient is critical in order to achieve successful treatment of the cohesive fill in situ.

 

Surface of completed lift after electroosmotic dewatering; inset photo shows close-up of surface

The result of the trial showed that the shear strength of fill in the form of a wet slurry could be increased to permit safe construction of a vertical reinforced soil wall. Another finding was that the reinforcement/soil bond increases in proportion to the increase in shear strength.

This use of EKG technology offers the potential for the use of very poor quality materials which are ubiquitous and otherwise represent a liability rather than an asset.

 

 

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