26-07-2012, 04:49 PM
Stabilisation of Black Cotton Soils Using Fly Ash, Hubballi- Dharwad Municipal Corporation Area
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Abstract
Urbanisation and growth in the economy of tier-2
cities of India have led to the steep increase in the building
construction activities and has necessitated the
implementation of infrastructure projects such as highways,
railways, air strips, water tanks, reclamation etc. These
projects invariably require quality earth in massive quantity. In
urban areas, borrow earth is not easily available which has to
be hauled from a long distance. Quite often, large areas are
covered with highly plastic and expansive soil, which is not
suitable for such purpose. The twin city of Hubballi-Dharwad is
a fastest growing tier-2 city of Karnataka state and is the
second largest city of the state just next to Bangalore. The
wide spread of the black cotton soil in the twin city of Hubballi-
Dharwad has posed challenges and problems to the
construction activities. A task was therefore undertaken to
investigate and improve the engineering properties of the
black cotton soils of Hubballi-Dharwad Municipal Corporation
area so that, a better understanding is facilitated for the civil
engineering practitioners, while dealing with these soils. The
West Coast Paper Mills, Dandeli (Karwar Dist, Karnataka),
located at about 60 km. from Hubballi-Dharwad generates
huge quantity of fly ash and the fly ash management is posing
serious problem.
INTRODUCTION
he black cotton soils possess low strength and
undergo excessive volume changes, making their
use in the constructions very difficult. The
properties of the black cotton soils may be altered in
many ways viz. mechanical, thermal, chemical and other
means. Modification of black cotton soils by chemical
admixtures is a common stabilisation method for such
soils (Bell, 1993). Among various admixtures available
lime, fly ash and cement are most widely and commonly
used for the stabilisation of the black cotton soils. Fly
ash contains siliceous and aluminous materials
(pozzolans) and also certain amount of lime. When
mixed with black cotton soils, it reacts chemically and
forms cementitious compounds. The presence of free
lime and inert particles in fly ash suggests that it can be
used for stabilisation of expansive soils (Indraratna
et.al., 1991).
REVIEW OF EARLIER WORK
A number of researchers have worked in
developing different methods of soil stabilization, which
are practical and economical. Amarjit Singh (1967)
reported the use of fly ash and lime for stabilizing soils in
road construction. Amos and Wright (1972) have
studied the effect of mixing fly ash with black cotton
soils. In the recent past, many researchers have carried
out experimental and field studies for the stabilization of
expansive soils using fly ash. Yudhbir and Honjo (1991)
stated that the pozzolanic fly ashes can be
advantageously made use of to improve the
geotechnical properties of black cotton soils.
Modification of black cotton soils by chemical
admixtures is commonly adopted method for stabilizing
the swell-shrink tendency of expansive soils (Bell, 1993).
Sivapullaiah et.al.(1996) reported that the addition of fly
ash decreased the liquid limit of black cotton soils and
studied the effect of fly ash on the index properties of
these soils from Karnataka, India. Bhoominadhan and
Hari (1999) proposed the use of fly ash in construction
works like brick making and soil stabilization. Cokca
(2001) studied the effect of fly ash on expansive soils
and he concluded that fly ash can be recommended as
an effective stabilizing agent for the improvement of
expansive soils.
MATERIALS AND METHODS
Liquid lim it
The results indicating the effect of varying
percentages of DFA on the liquid limits of selected black
cotton soil samples are presented in Fig.2.
The liquid limit decreases with the addition of fly
ash. The results show a considerable decrease in the
liquid limit upto 30% increase in the fly ash percentage
(i.e. M 30 mixes) and then after the decrease is
observed to be marginal for further increase of fly ash
percentage. The liquid limit of the black cotton soils is
essentially controlled by the thickness of the diffused
double layer and the shearing resistance at particle
level. The addition of fly ash results in the decrease of
liquid limit due to the effect of reduction in the diffused
double layer thickness as well as due to the effect of
dilution of clay content of the mix. The decrease of liquid
limit becomes very marginal or nil beyond 50 – 60 % of
fly ash. This is due to the increased dilution effect i.e.
due to the increased percentage of coarser size
particles in the mix because of the increased
percentage of fly ash.
CONCLUSIONS
Based on the results of the investigation,
following conclusions are drawn.
i) Dandeli fly ash is used as a stabiliser for
improving the geotechnical characteristics of Hubballi-
Dharwad black cotton soils. Addition of Dandeli fly ash
significantly improves the index properties, compaction
and strength characteristics of black cotton soils
understudy and the effects of fly ash treatment vary
depending upon the quantity of fly ash , that is mixed
with the study black cotton soil samples.