Engineering Enigma

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The narrow gorge that houses J&K’s most modern dam continuously surprised the people tasked to tame the ferocious Chenab in one of the most unstable mountain ranges. While retrieving the project in 2005 from the brinks of a literal collapse, at huge costs, the engineers did something perhaps for the first time in the world, reveals Masood Hussain

Decimated: In August 2005, the once-in-1000-year flood in Chenab overtopped the dam, creating a situation that it led to massive cost and time over-runs.

Decimated: In August 2005, the once-in-1000-year flood in Chenab overtopped the dam, creating a situation that it led to massive cost and time over-runs.

“It was just a switch that delayed the testing of the unit-VI for five days,” Abdul Wahid, Chief Engineer (civil) Baglihar, said. “In a power project, the whole thing is like a puzzle; we do one thing and get into another level.” The switch-hunt spanned almost half of the world till it was traced down-south in India!

For a naked eye, Baglihar is visible to the extent of dam. It actually is located in a mountain hollowed for over 14 years. These mountains house gigantic concrete 7-storey structures that are almost half of the Srinagar’s civil secretariat and require elevators. The first phase alone has more than 124 kms of cabling and if one switch malfunctions, nothing works. In power projects, where thousands of items are sourced from different vendors across the world, even assembling them is a challenge, engineers admit.

Wahid remembers the frustration that resulted in the failure of efforts to pull out stop-lock gate of the power intake. “We did not anticipate the load of silt blocking it. We put special pumps 22 meters under water but failed,” Wahid said. “Then we got expert divers who took 10 days in only loosening the silt wall. Finally, one of the gates fell down on the dam bed forcing us to fabricate a new one.”

Every project has its complicacy but various projects have part of its problems linked with its location. Those peculiar issues were identified by Raymond Lafitte, a professor at Federal Institute of Technology in Lausanne (Switzerland) when World Bank appointed him as Neutral Expert (NE) to settle ‘differences’ between India and Pakistan.

Baglihar is a narrow valley with poor geology, a high flood discharge and massive sediment yield. Apart from requirements for dissipating high volume of energy – that equals nearly the output of 10 nuclear plants of 1300 MWs each during floods, the reservoir is small in comparison to flood discharge. Besides, the site is in an area of high seismicity. But the NE agreed that creating three separate plants of 150 MW each would cost higher, so the project is located ideally.

All these problems contributed to a literal collapse in 2005 summer. Apart from a meter of snowfall recorded on the site, perhaps for the first time in February 2005, the catchment of the project recorded 800 mm of rains against a recorded high of 400 mm. By June the discharge touched 4000 cumecs that surged to 6230 cumecs in July. Last major discharge was recorded at 7500 cumecs in 1950.

By then, project was almost half through. Of the 143 meters height of dam 70 meters were complete. Sustained high flood ran havoc, caused serious erosions and scouring along river banks disturbing their natural equilibrium and monsoon complicated it further. Soon, drawdown conditions paved way for sudden rock and debris slides.

“It was a nightmare,” says   Rajvanshi, JP’s oldest on-site officer. “Every day we were waking up to a new crisis and literally nights were sleepless.” Water came so swiftly that the contractor barely managed salvaging Schwing Batching Plant, silos, shuttering and other equipment from the plunge pool. JPA promoters personally flew to oversee rescue.

Basharat A Dhar, then Secretary Power, was on his way to office, when he got the call that Chenab is exploding. “I told driver to drive me to Ramban,” Dhar said. “It was horrifying to even approach the site as the river with massive discharge was falling from a height creating a threatening impact.”

On June 21, 2005 the plunge pool was flooded. On July 2, 2005 the 105 meter long crucial steel bridge downstream of dam was washed away. On July 7, nearly 300 meters of Nashri bye pass on left bank eroded completely into the river blocking any movement on that side.

Hole-in-DamThe worst was witnessed by the two diversion tunnels (DT). Draining 1500 cumecs each, DTs are crucial for dam construction. With 10.5 meters diameters, one was 385 meters long and another 530 meters. Both were taking off at an elevation of 709 masl. Executed by applying NATM excavation, DT1 started functioning early in 2002 and DT2 in 2004.

On July 5, DT2 was completely blocked due to rock collapse above its inlet area. With the dam overtopped already, the second shock came on August 8, 2005 when DT1 was also blocked. With more water overflowing the dam structure, the cable track and cranes were also damaged, severely.

The destruction was visible on the right side of the dam where the high-velocity river’s massive fall with an average 4000 cumecs from 65-meters height created a nearly 30-meter deep hole. “The whole area was severely vibrating by the impact of such an enormous fall,” remembers Zahoor A Chat, the then SPDC Executive Director. “This side witnessed maximum damage because the concrete level for main Dam was lowest on this side.”

In absence of energy dissipaters, the waterfall would hit the dam foundations; hollow it, thus creating a situation that the dam was literally hanging. Its foundations were hollowed up 30 meters and it was a looming threat. It was during one inspection that a top engineer of the Lehmayer International GmbH (LI), the consultants for PDC, named this hollow as ‘black hole’.

Dam overtopping prevented any work on dam’s six of the 18 blocks. Against an estimated 1.9 million cubic meters concreting, the main dam structure already had 1.1 million done. With Rs 2800 crore spent against an anticipated project cost of Rs 4000 crore, SPDC was literally frustrated. Officials managing the project admit, even now, that they took it as beginning of the end.

“The crisis has pained everybody,” admitted a senior LI engineer. With six engineers on the spot, LI flew its top hydrologists from Germany. JPA flew some experts from Austria. It hired deep water divers to explore if the DTs were cracked or blocked. They, however, could not dare to get in given the fast flow of discharge, 32 meters of debris and a depth of around 74 meters. Delhi sent a team of the Central Water Commission (CWC) geologists to help arrive at a consensus. By then, State’s Economic Adviser Dr Haseeb Drabu was appointed to head the Committee and manage the crisis.

Even a tunnel collapsed and had to be rebuilt.

Even a tunnel collapsed and had to be rebuilt.

With a big no to blasting because of instability in the range, then, five options were on the table: unlock the DTs, create a third DT while making efforts to unblock the two DTs, use giant pumps to drain the dam at exorbitant costs, convert the inspection tunnel into a DT for the time being and finally bore a hole into the main dam structure to drain the dam and reduce the levels so that work can resume. LI had suggested reducing the height of dam’s block No 11 by 10 meters (from elevation 764 masl to 754 masl) to accelerate quick drainage.

After a series of meetings in Srinagar, Delhi and on-site, the engineers choose an option that was perhaps the world’s first – boring a hole into the dam itself! This was in addition to starting work for DT3 on the left side of the dam besides introducing a faster Rotex system for concreting. It was immediately imported from Australia. At the end of priority was rehabilitating the collapsed right bank slopes up to elevation of 845 masl and filling of the ‘black hole’.

“Boring the dam itself was not an ordinary decision,” an engineer, who wishes to stay anonymous, said. “We installed a series of high-tech instrumentation within the dam structure to get bits of information about the health of the structure as blasting under controlled conditions was taking place. It was literal ultra-sonographic equipment and we knew what is happening inside.” Central Mining Research Institute (CMRI), Dhanbad experts flew from Bihar to monitor the hole-making that started in September 2005.

At Baglihar, January 14, 2006 was important but a tense day. That day, the 100 meter long 6.8 meter diameter hole in Block 11 was completed. “Last main blast was taken with remote control simultaneously from both sides,” Chat remembers. It started draining 580 cumecs of water. A dam that was overtopped for six months stopped overflowing in three days. Already, the discharge had ebbed to the winter levels. But the desired goal was not achieved. Expected to reduce the water level from 760 masl to 740 masl so that choked tunnels are approached, the outlet reduced the level to 757 only. Experts attributed it to “some obstacles” at the mouth of the outlet.

Shock: When the water was diverted, it shocked everybody to find the floods had hallowed the dam and it was hanging for many years.

Shock: When the water was diverted, it shocked everybody to find the floods had hallowed the dam and it was hanging for many years.

The major relief came later. Dam overflew during 2006 monsoon as the sluices were operational shortly before 2007 monsoon set in.

Situation improved greatly that encouraged a series of quick decision-making. Creation of 528 meters long DT3 with a diameter of seven meters was abandoned at a time when the men and machinery was almost 50 meters inside. Project managers admit the decision of going for DT3 was dictated by a sense of initial hopelessness. “Initially DT1 and DT2 were planned on the left bank but these were shifted to right bank because of poor geology,” one insider said. “DT3 was abandoned for poor rock mass quality as huge slope debris and large scale rock mass failures were making it tougher.”

Efforts to reopen DT1 and DT2 were also given away. Reason: the unpredictability that could be experienced during excavation under saturated conditions besides uncertainty while taking the final blast under water at the inlet of DT3. The damaged Nashir Byepass Road stretch was left untouched and a 730 meters tunnel resumed the movement.

With confidence restored, new alternatives were considered. In order to ensure smooth dam construction and literal reconstruction of the plunge pool, a new river diversion arrangement was decided. It envisaged four temporary sluices – 3.5 x 8.2 meters in Blocks-12 and 13 besides extending the chute spillway channel in Block-4 beyond flip bucket by 120 meters below downstream coffer dam.

Changes came with time and cost overruns. The requirement of concreting the dam and intakes that was estimated earlier at around 21.82 lakh cubic meters would now touch 2.8 million. The crisis added Rs 1200 crore to the project besides owners lost a whopping sum as the project deadline was delayed by 22 more months. A daily earning from Baglihar (stage-I only) is more than two crore rupees a day. Cost overruns impacted the earlier-negotiated tariff structure with lenders. A new series of negotiations, and agreements started.

Amid near normality on-site, another issue cropped up in February 2007 when a massive collapse took place inside the tail race tunnel (TRT) of phase-I. It took some time for the stakeholders to manage a way-out. JP proposed reducing the width of the TRT from 10 to 9 meters to abandon removal of undercut. Since it will lead to a head loss of 85 cms against JPs estimate of 48 cms, LI suggested the loss be compensated by raising MDDL from 835 to 836 masl. But insiders said it was just a small issue that was managed successfully in a couple of brainstorming sessions.

The real technological challenge that the project confronted in January 2008 was plugging the dam hole and the four temporary construction sluices. It had to be done in flowing discharge conditions. On March 23, 2008 a huge steel bulkhead, much larger than the outlet, was lowered from the reservoir side. While hydraulic pressure from behind helped it plug, engineers dumped a lot of debris to get additional lateral support to gigantic steel structure. Though it plugged the hole, huge leakages continued causing water flashes inside the hole.

“In the bore, we laid a 2.5m thick temporary bulkhead of bags filled with dry concrete that acted as a solid shield after setting. It reduced water turbulence and paved way for final plugging,” Chat notes. “There was another round of proper concreting a few days later and finally pressurized chemically treated concrete grouting was done to plug any micro openings and hair pin cracks.” By July 18, the process was over. All the pipes inserted earlier to drain the seepage were sealed except one left unplugged to safely drain the leakages, if any.

The next stage was to seal four temporary sluices. Since these sluices had gate-grooves, the follow up was easier. Sluice-sealing continued between September 15, 2008 and February 21, 2009.

But plugging of the already blocked DTs was challenging and took a long time between December 1, 2007 and May 6, 2008. In the main design both the DTs had gates but the mass sliding buried the gates under debris forcing creation of alternatives.

The ‘black hole’ still remained the main threat even after the then Prime Minister Dr Manmohan Singh formally inaugurated Kashmir’s new temple of power on October 10, 2008.

It was only after the power house went into generation and the discharge had adequate exits as designed, the real damage of the plunge pool and the right bank were actually assessed. Dewatering of the poll in November 2008 shocked stakeholders: the dam structure was literally hanging in air for almost 40 months. It required almost seven lakh cubic meters of concreting to restore it to the pre-flood status.

As all the three units of the stage-I went into generation, the technological challenges did not cease. Project’s Stage-II with the same installed capacity of 150 x 3 MWs sources water for its turbines from the same dam and interestingly both the power stations are in the right bank mountains.

In 2007 summer, design part of the power intake (tunnel that feeds turbines) for stage-II became a major issue of debate within engineers. LI engineers suggested two units of 225-MWs each instead of three units of 150-MWs each as envisioned in the main design.

Engineers in SPDC disapproved the idea. Their argument was that available discharge is not to the extent of running even a single unit of 225-MW at particular time of the year which will lead to huge generation losses.

Geologists studied the rock-mass again and opined a threat to Stage-I power station if blasting for Stage-II excavations added to the strong vibrations set by the operational turbines. Incidentally, tunnels to both the stations cross each other with only 21 meters of rocks in between. JPs Rajvanshi said they have treated this patch specially to improve its strength as 430 cumecs of water are flowing on either side of this rock belt.

Finally, SPDC set up a high-powered technical committee under CEA’s member (hydro) which upheld the main design. Blasting was carried out in a controlled situation to reduce any distress of the weak geology of the mountain.

With entire project almost implemented, the design debates continue. During peak summer months, for around 100 days, Chenab has more water and around 500 cumecs spills over. Project’s two stages require 430 cumecs each. This has triggered a division within. A section says it would feed another stage of 450 MWs and that can be set up on dam’s left bank. But there are strong responses from engineers who do not want it to happen. They say left bank’s poor geology can trigger a major crisis. In coming days, SPDC may have to formally set up another committee to explore the technical feasibility of another stage.

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