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CONTENTS:
o Introduction
o What is electro kinetic geo synthetics?
o Principle
o Applications
o Slope stabilization
o Case study
o Conclusion
INTRODUCTION:
o Geo synthetics are used in civil engineering to
carry out a range of functions.
o All of these functions are limited by the rate at
which water is able to flow.
o New applications for geo-synthetics provide
an active role in established functions.
Electro kinetic geo synthetics
o Electro kinetic geo synthetics (EKG)can
be achieved by combining the electro
kinetic phenomena of electro-osmosis,
electrophoresis and associated electro
kinetic functions such as electrolysis with
the traditional functions of geo synthetics
of drainage, filtration, containment and
reinforcement.
PRINCIPLES OF ELECTRO KINETICS
Electro osmosis: water transport from anode to cathode
APPLICATIONS:
o Strengthening of slopes and cuttings.
o Electro kinetic consolidation.
o Dewatering of sewage sludge.
o Dewatering and recovery of water from
mine tailings.
EKG FILTER BAG&EK DRAINAGE BAG
EKG electrodes for slurries/sludge dewatering and cutting/slope stabilization.
EKG electrodes for planar conditioning in sports turf/agriculture applications.
SLOPE STABILIZATION
The concept of EKG strengthening
of a slope is based on :
oThe orientation of the electrodes
is selected to intercept any
potential failure plane.
oElectro-osmotic treatment results
in an immediate reduction in pore
water pressure and accelerated
dewatering of the slope which
results in an increase in the shear
strength of the soil, reducing the
risk of a slip plane developing.
Concept of Electro-osmotic
consolidation.
CASE STUDY:
Electro kinetic geo synthetic (EKG) technology has been used to successfully stabilize a failing clay embankment in London resulting in a 26% cost reduction and a 47% reduction in carbon footprint over conventional methods.
o A trial was conducted on a 22m stretch of
a 9m high Victorian embankment. The
embankment had been constructed by end
tipping a mixture of weathered London
Clay and other material such as brick and
stone fragments onto underlying alluvium
and terrace gravels.
EKG TREATMENT
EKG treatment was designed to accommodate either of
the identified failure mechanisms. The treatment was
based around an array of EKG electrodes installed at 2m
centers in the form of tessellating hexagonal cells, with
the hexagon being defined by anode stations and a
central cathode
EKG anode/cathode installations using a P45 drill rig.
Results after treatment:
o Dewatering from the cathodes >25 times that from control drains.
o A reduction in plasticity and shrinkage characteristics.
o An increase in groundwater temperature from 10°C to 20°C.
o A modest DC power consumption of only 11.5kWhrs/m³ of soil treated.
o Improvements in shear strength parameters (c’ and Φ)
o A 263% improvement in the bond strength of the anodes acting as nails
o A cessation of slope movement.
o Following EKG treatment the anodes have been retained as permanent soil nails and the horizontal cathodes retained to act as permanent drainage
Analysis :
Analysis Reinforcement FoS (ULS)
Pre treatment
(TGP data)No 0.81
Pre EKG treatment No 0.96
Post EKG
treatmentNo 1.47
Post EKG
treatmentYes 1.71
Slope stability analyses were undertaken pre and post treatment. The
analytical results are shown in the table below.
Longevity of treatment
The use of EKG to stabilize slopes is a long term solution because:
o Soft weak embankment materials consolidate and improve in shear strength with EKG treatment. This consolidation is permanent.
o Additionally, EKG treatment works best on these soft materials, which are critical to the stability, and in this way the treatment can be considered ‘self selecting’
o Enhancement of soil/reinforcement bond is a long term effect.
o Passive drainage (de-activated cathodes) is retained in the slope.
Costs
o EKG treatment produced total project cost savings of 26% than lowest cost alternative of gabion baskets .
Carbon Footprint
o A carbon footprint comparison of the EKG and conventional treatment options showed 47% lower emissions by using EKG.
Dewatering of sewage sludge
(a) Conventional treatment, 19% dry solids content; (b) EKG enhanced treatment, 31% dry solids and 39% volume reduction.
Dewatering of mine tailings
Disposal of kimberlite slimes Dewatered tailings (78%) dry solids.
Conclusion
o Active geo synthetics in the form of
EKG materials open up a new range
of applications for geo synthetics.
o EKG applications relate to a number
of main drivers including legal
requirements, climate change, the
need to reduce carbon footprints,
reclamation of water and reduction
and reuse of wastes.
References:
o Mumtaz .m et.al,Performance evaluation of
coir as electro kinetic geo textile.
o Colin j.f.p.jones et.al,Electro kinetic geo
synthetics in hydraulic applications.
o Huntley ,D.T& Lamont-Black ,J, Economic
models for the use of electro kinetic geo
synthetics.
o Mumtaz M et.al ,Electro kinetic geo textile
stabilization of embankment slopes.