Peat settlements and decompositions due to changing weather and


            Peat is one member of soft soil family and is a highly
organic one. Mainly, peat is contained with organic matters such as partially deteriorated
plants, leaves and parts of dead animals. Generally, peat shows unique
geotechnical properties with compared to other inorganic soils such as clay and
sand which are contained only soil particles. Peat is very common type of soil
all over the world. The total land area which contain peat is about 4.5% of
total land in the world. Some characteristics of peat are;


High natural moisture content (up-to 1000%)

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High compressibility

Low shear strength

Potential for further settlements and decompositions
due to changing weather and environment conditions


            In constructions such as Highway subgrade and
embankments, peaty clay is a major issue due to its own properties. Because,
those properties are not counting with engineering properties which needs for a
quality construction. Mainly such soil with higher moisture content may leads
to considerable difficulties to achieve a suitable degree of compaction, for
consolidation, for compression strength which need for particular construction
procedure. In addition, low bearing capacity and slope instability are also
main problems which identified in constructions with peaty clay.


            Due to those reasons, soft clay is a major challenge
faced by Sri Lankan engineers same as other engineers in world. This soft clay
is extremely compressible and low in shear strength. Therefore, finding a way
to stabilize such soils was a major need for Industry for a long time. Vacuum
consolidation, Electro osmotic consolidation and Deep- mixing are some methods
in present.


            Deep-mixing is a popular method in soil stabilization and
is conducted using cement as a chemical additive in the industry. Due to the
higher cost associated in using cement as an additive, researchers (Mousavi, & Wong, , 2016), (Abdullah , Mohammed, &
Ahmed , 2017)
have used different other alternatives to overcome this problem, such as Kaolin
clay, Slag dust, CCR and FA, etc. The Sri Lankan researchers have investigated
soil stabilization with by products such as Rise Husk Ash (RHA) and Fly Ash
(FA). Instead of using cement. However, the improvement observed from those
additives were not satisfactory. The main reason is that the required amount of
Calcium content for a proper pozzolanic reaction is not sufficiently available
in those additives. Specially, the fly ash produced from Norochcholai Power
plant belongs to Class F, which low calcium fly ash (around 10%). Hence, it is
required to add an additive which is high in calcium in order to improve the
performance of using FA. In literature, there are some studies conducted using
calcium carbide residues (CCR) as a high calcium additive with FA.


            CCR is a by-product of PVC, Polyvinyl alcohol and
acetylene gas industry. CCR is produced by hydrolysis reaction of calcium







Most of researchers
have identified CCR as a law carbon and less energy intensive material. In real
case, CCR is the sludge of acetylene gas product. Therefore, using CCR for
stabilization methods is a good trend for removal of that sludge amount. Further,
it has observed considerable stabilization of soft soil by using CCR together
with FA. For example, (Suksun , Chayakrit, Avirut,
& Arnon , Strength
developmentinsiltyclaystabilizedwithcalciumcarbideresidue, 2013). But, there is no
records of using CCR as stabilizing agent in Sri Lanka. Therefore, this
research will continue with CCR as a high calcium agent in deep-mixing with FA.



Problem Statement                                                                


            Peaty soil is highly compressible and contains high
moisture content as mentioned in introduction. Due to that reason peaty soils
have very low shear strength, low bearing capacity and tends to unacceptable
settlements. Therefore, this is a major issue in civil construction industry
and peaty soils are challenge for engineers all over the world same as Sri
Lanka. There are several reasons for these issues as high organic content of
peat soil. Therefore, it’s needed mechanical stabilization or chemical
stabilization for peaty soils to overcome such issues.


            Deep-mixing method is a very popular stabilization method
which use in the world. However, cement is the stabilizing agent in most of
cases we experienced. The reason for that is cement was succeeded as an agent
rather than other agents such as RHA or FA. But, using cement was not an issue
in past due to availability of cement and as a cheap material. In present that
situation is totally different. Cement using as a stabilizer is not economical
considering the amount of cement needed for stabilization procedure in vast
construction projects. Therefore, finding an alternative for cement is a major
problem in civil construction industry.



Significance of the research                                                          


            Currently used alternative, FA (class F which is
available in Sri Lanka) is not sufficient due to the low calcium amounts to
improve the soil stabilization process. Hence, there is a crucial need of
selecting a calcium additive to increase the performance. Therefore, studying
about the applicability of CCR is important. Further, both CCR and FA both are
waste products of acetylene gas industry and power plants respectively. FA is
used as a sub-material for cement industry in Sri Lanka. However, CCR has not been
used for any other work in Sri Lanka, currently, is non usable waste which
makes some difficulties for acetylene gas industry. They have no authority to dispose
this CCR as a waste to nature. Because, it’s known as a pollutant of ground
water and ground surface. Using CCR for deep-mixing in soil stabilization
method is a good solution for removal of

 as a waste.
Finding a solution for CCR as a waste is a major aspect of this research.


            As mentioned earlier
cement is not an economical material to use as a stabilizer in deep-mixing
method. The construction industry is looking for economical, sustainable
solutions. Though cement is the best solution for deep-mixing method which
gives high compressible strength and shear strength, contractors have to spend
much for cement. Therefore, looking for alternative for