Oct - Dec 2009 • Vol. No. 32 Issue No. 2 • - L&T Construction

stock pile. The center-to-center distance of the Monolithic construction of side walls, hopper
existing and proposed Track Hoppers were 32m and and top frame beams
was at a distance of 18m from edge of the existing
coal stock yard retaining wall. It left a working space
Construction from bottom to top method
of mere 3 to 8 m from the edge of raft to these existing Use of crane with skip bucket
structures.
The top crust of the proposed Track Hopper was
filled up with service road, drains, lighting mast, RCC
pavement, underground service water and sewer
Use of long boom excavator
Sheet pile driving
lines. Since there was no space for approach road, Initially the sheet piles were designed based
there was congestion in the movement of man, on dry soil condition with top 5 m as open
material and resources. and thereafter leaving earth (1:1 slope) for
passive pressure and without any struts. But
Another limiting factor was that ground water table was due to prevailing soil condition at site this was
just about a meter below the FGL and the nature of soil found to be ineffective at execution stage and
was mainly a complex mixture of silty clay and sandy silt finally a revised design was prepared with
with 'N' value more than 100 near foundation bottom. struts.
The prevailing soil condition at site was highly
saturated. Disposal yard was approximately 5 km away
from the site and is surrounded by frequently operated
MGR line (railway track). Excavation was allowed upto 1
m above the water table for safe movement of machinery,
which was done through 24x7 water table monitoring by
sounding technique. For this additional boreholes were
made in various segments of Track Hopper area.
Techniques adopted to overcome the
challenges
Sheet pile and strutting work
Deep bore well dewatering system
Mechanized deep excavation
Doka Formwork with water stop tie rod
arrangement
Water jetting for installation of sheet piles
Castellated beam for Structural Steel work of
track hopper shed
To lower the water level, extensive de-
watering had to be done, which resulted
indensification of hard strata and dry
condition of soil having 'N' value more than
100. A complex pile driving technique, in
combination of Vibro and Impact hammer
with water jetting / trenching was adopted.
Extensive monitoring and carrying out of
remedial measures for the deflection of struts,
which continued throughout the Track Hopper
construction.
Despite all odds, the entire construction of
Track Hopper was completed in 18 months
including all the associated and finishing
activities.
Sabyasachi Sarkar
Joint General Manager (BMH)
Jaydeep Goswami
Manager (BMH)
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ECC Concord Oct-Dec 09