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NTPC
KORBA
- CASE STUDY
CICO CHEMICAL
GROUTS - A New Concept in Solution of Serious Water Ingress Problem
NTPC Entrusted
CICO - A Problem of Stopping Heavy Leakage
At the time of
commissioning of the 2nd 500 MW unit of Korba Super Thermal Power
Station, serious problem of water ingress came up at the Ash Slurry
Pump House.
Due to some
constructional factor, the sump Pit of the Ash Slurry Pump House was
heavily leaking. All general methods were attempted by NTPC
authorities and the contractors to stop the leakage but none of the
methods worked at all.
CICO took up the
challenge and the problem was understood by our team. The site was
inspected and our proposed technical solution to arrest the leakage
was submitted to NTPC authorities and the same was accepted. CICO
executed the repair job successfully, without reconstruction of the
structure resulting in enormous savings in time and cost over-runs.
The NTPC authorities confidently commissioned the 2nd 500 MW Unit.
The
problem
The Korba Super
Thermal Power Project of NTPC is situated on the banks of the Hasdeo
river and the site is surrounded by several canals leading to high
subsoil water level.
The Ashy Slurry
Pump House facility is 13.5 metres below the ground level. The pit
size is 20m x 12m - with a Sump pit of 3.2m x 2.2m x 1.9m.
CICO was briefed
that during the excavation work, flowing water in the sub-soil was
observed. The raft of the entire structure was constructed in parts
by diverting the flow of water to overcome the problem of flowing
water had washed out all the fines and cement, causing heavy leakage
through the sump pit wall.
CICO's
Observation
After stripping
off the shuttering, large voids/cavity in the northern wall of the
sump pit was observed. The water was gushing out through this cavity
with high pressure. The volume of leakage was observed about 550/600
litres per minute. Several pumps with an accumulated capacity of
120/150 HP were installed. The water which was being pumped out, by
these pumps was sufficient to maintain a constant water level in the sump.
CICO's
Recommendation
Having inspected
the site CICO's recommendation to NTPC authorities was to do curtain
grouting on two sides (Northland East) of the sump with CICO
POLYGROUT to form an impervious barrier to stop the water ingress.
Chemical curtain
grouting with CICO POLYGROUT was to be done after reducing the volume
of leakage by 'Cement Grouting' admixed with an 'accelerator' and
plugging the entire leakage area by channelising the entire flow of
water through fixing suitable nozzles.
The scope of
"Cement Grouting" was given to a separate Agency. However,
the accelerator used for grouting was supplied by CICO.
CICO
Assigned the Chemical Curtain Grouting
NTPC authorities
being thoroughly convinced about CICO's recommendation to solve the
problem of water ingress, awarded the chemical curtain Grouting work
using CICO POLYGROUT to CICO.
How
CICO Went About
Cement grouting
operation conducted by another agency could not achieve the desired
results. According to them due to streaming action, the cement grout
was being washed out. The efforts to get high capacity pumps to
dewater the sump pit was not successful. Addition of more small,
capacity pumps was not a practical proposition in view of the size
limitation of the sump pit and the problem of erection of Suction Pipes.
CICO
Has to Face a Severe Handicap and Proceed
It was not
possible to reduce the flow of water or to empty the sump by
dewatering for plugging the leakage and to channelise the flow of
water through pipes to take up chemical grouting.
CICO's
Proposed Action to Overcome the Constraint
CICO discussed
this constraint with NTPC engineers and proposed to start chemical
curtain grouting by plugging the leakage points by means of stacking
sand bags into the sump to a thickness of 600mm on both northern and
eastern ends. CICO proposed to channelise the flow of water through
PVC pipes fixed, while placing the sand bags and strutting steel
plate barrier to retain the sand bags.
NTPC
Engineers Accept CICO's Proposal
The above
make-shift arrangement was accepted by NTPC engineers. This
preparatory work was completed and CICO POLYGROUT injection operation
commenced. A total quantity of 285 litres of CICO POLYGROUT was
injected. The pressure of the flowing water was so high that CICO
POLYGROUT could not gel as even few seconds time required for gelling
was not possible due to the high discharge of water.
Alternative
Steps Taken
Subsequently,
another steel plate was fixed on the eastern wall of the sump pit
1.10 metre apart from the northern concrete wall. The gaps in between
were kept in the sand bags to act as a passage for the leakage water
to flow out., thereby making room for injection of CICO POLYGROUT on
the raft after making through and through holes on its surface well
apart from the edge of the sump pit. Seven such holes were drilled on
the raft and nozzles fixed. 615 litres of CICO POLYGROUT was injected
through these holes. The volume of the leakage was reduced to 40% .
Since the plugging of the leakage point was not exactly on the source
of the leakage point some quantity of CICO POLYGROUT came out. BUT
CICO had succeeded in reducing the leakage.
CICO's
R&D Team Gets Involved for the Solution
The entire
situation was reviewed by us and we came to the conclusion that a
large quantity of CICO-POLYGROUT would be required to stop the
leakage of such a magnitude, so as to make the curtain grouting
totally effective. However, this was going to be tremendously costly.
Therefore we evaluated thoroughly the usage of different grout
materials and approached our R&D Wing to suggest a right and
economical grout to stop the leakages at the sump pit had to have the
properties of being liquid, and flowable to be injected in, but also
solidify on coming in contact with water and form a high density
material to withstand streaming action and to avoid getting washed out.
CICO
R&D Wing Evolves the Solution
CICO's independent
Research and Development wing studied the problem and gave a solution
for use of an appropriate Grout material to be injected to fill up
the huge void, and confine already injected POLYGROUT to form a
barrier in water leakage path, alongwith the other quantities as
outlined, and yet be economical.
"CICO
HOT MELT" - Was the Answer
CICO's R&D
wing recommended the use of our of our own compound had to be made
hot and melted. This molten grout material was to be grouted through
the nozzles by pump.
CICO Hot Melt
grout is Asphalt based and processed to perform the designed purpose.
SIMULATED
Tests
CICO's R&D
Wing conducted several trials with CICO HOT MELT in simulated mini
models of the site, before to do final grouting operation with CICO
HOT MELT.
And
Finally
We carried out
CICO HOT MELT operation at site, by making through and through holes
in the raft, well apart from the edge of the sump pit Enabling 'CICO
HOT MELT' Grout to fill up the void of the water path and also press
the POLYGROUT injected earlier, towards the leakage points. 18
through and through holes were made in the raft. Nozzles were fixed
up. We started 'CICO HOT MELT' Grouting operation within 8 weeks of
assignment of this very complicated work to CICO by NTPC. On the
first day itself 1120 kg of CICO HOT MELT was grouted.
With CICO HOT MELT
grouting, 20% of the water leakage was stopped. We continued CICO HOT
MELT grouting operation untill water leakage was reduced by 90 to 98%
of the initial volume of leaking water, 6560 kg of CICO HOT MELT
grout was injected through the nozzles.
From 550/600
litres per minute, the volume of leakage was reduced to 20/25 litres
per minute. And this reduced volume of leaking water, also comprised
of the leaking water coming from pumps running at the Ash Slurry Pump
House. The NTPC executives inspected the satisfactory progress
achieved by CICO at site.
CICO did not stop
there itself. A thorough and minute checking of the sump pit was done
CICO POLYGROUT injection operation. 71 litres of CICO POLYGROUT was
injected through these 4 nozzles and that stopped even minor leakages also.
NTPC
- A Thorough Satisfied Client Now
CICO has earned
the confidence of the NTPC authorities by executing the project work
to their total satisfaction. |
