11-01-2014, 05:00 PM
PREFABRICATED COIR GEOTEXTILE VERTICAL DRAINS
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INTRODUCTION
Construction of unpaved roads in rural areas in many of the cases are accomplished
by forming embankments along the banks of the paddy fields or swampy areas and
hence the construction of roads and embankments arc so closely interconnected that
one may not be able to visualise the two constructions independently. One of the
major difficulties in these constructions is the presence of saturated soft clay and only
very poor soil will be available for construction and hence some sort of ground
improvement techniques should be resorted to facilitate speedy and uniform
stabilisation of the soft soil.
Of the various methods of ground improvement techniques available, pre-Ioading is
the most successful one. The main disadvantage of this method is that, the time
required for consolidation is very long and also the surcharge load required is
significantly high. In many cases to pace with the speed of construction activities pre -
loading may not be always a viable solution. In such cases, the presence of vertical
drain can greatly reduce the pre - loading period. Installation of vertical drains results
in the reduction of the length of drainage path in radial direction.
PREPARATION OF COIR GEOTEXTILE DRAINS
Two types of coir geotextile drains were developed in the present research work. One
is of circular type and the other is of rectangular type. The circular drains \vere made
by wrapping the coir geotextiles twice over 50.8 mm diameter rigid PVC pipes. To
keep the geotextiles in position, it is tied by binding wires at 200 mm to 250 mm
intervals. For easy penetration of these drains a perforated metallic cone was made.
Preparation of Test Set· up
A steel tank of size 650mm x 650mm x 850mm was fabricated using mild steel plates
and mild steel angles. Bracings were provided on the sidewalls in the diagonal
directions to prevent buckling of the plates during loading. Inside of the tank was
painted with glossy metallic paint to have a smooth surface, in order to nullify the
thclian between the soil and inner surface of the tank . Clayey silt was used for this
test programme. The soil was soaked in water for 3 days and made into a thick sluny
form. The slurry was transferred into the tank in small quantities and was stirred well
to remove the entrapped air to the maximum possible. This was continued until soil is
filled in the tank to a depth of 700 mm. Three days rest period was given before
commencing the experiment.
SUMMARY
In general, the time for consolidation is very much reduced due to the provisions of
circular and rectangular coir drains in all the contigurations tested. While comparing
the performance of the types of coir drains, it is seen that drains using H2M8
perfonned better than that of H2M6 eoir geotcxtiles. Also the triangular configuration
is found to be more efficient than the other patterns trit:d. M uch better result was
obtained with circular type of drains compared to rectangular type of drains.