04-07-2012, 12:44 PM
STABILIZATION OF EXPANSIVE SOILS USING FLYASH
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ABSTRACT
Infrastructure projects such as highways, railways, water reservoirs, reclamation etc. requires earth
material in very large 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. Extensive laboratory / field trials have been carried out by
various researchers and have shown promising results for application of such expansive soil after
stabilization with additives such as sand, silt, lime, fly ash, etc. As fly ash is freely available, for
projects in the vicinity of a Thermal Power Plants, it can be used for stabilization of expansive soils for
various uses. The present paper describes a study carried out to check the improvements in the
properties of expansive soil with fly ash in varying percentages.
INTRODUCTION
For construction of an ash dyke at Ennore, North of Chennai city, it was found that the entire area is
covered with plastic clay having liquid limit varying from 33 to 50%. The area was being used for
cultivation and during summer, extensive shrinkage cracks exceeding 10mm width were noticed on
the surface. The soil was not suitable in the present form for construction of ash dyke due to the
following reasons:
1. Poor workability for compaction. The construction schedule was critical and it was necessary
to carryout the work during monsoon when optimum moisture content cannot be achieved.
2. High compressibility and leading to dyke top settlement.
3. Inadequate shear strength for required slope stability.
IV FIELD TESTS
Field trails were carried out by constructing an embankment measuring 3 to 4m wide and 30m long.
The height of the embankment was about 600mm. Each layer of 200mm loose thickness was placed
with varying fly ash content. To achieve the desired fly ash content, the layers were placed such that
fly ash layer is sandwiched between two soil layers as per the details given in Table 4.
For each trial mix, the required thickness of borrow soil was manually spread first. Above this, fly ash
collected from the ESP of the Thermal Power Plant was spread. This was again followed by a third
layer of soil. The layer of fly ash was sandwiched between two layers of soil to prevent it from flying
off.
After this, a disc harrow equipment shown in Fig. 3 was used for uniform mixing of soil and fly ash.
This equipment is a circular disc, which penetrates through the loosely placed layers and pulled
horizontally by a tractor. The discs rotate in such a fashion that the soil is shuffled and mixed
thoroughly. It was observed at site that after about eight passes of the disc harrow, the dry mixing of
the two materials was quite satisfactory and with uniform colour of the mix.