Working in India: Anatomy of a Hydro Project - Desilting Chambers and Tunnels (Part 7)

The waters of the Satluj River in the Himalayas of Northern India transition from green in the winter, when flows are low, to chocolate brown in summer when snow melt higher up causes flows to ramp up and the river carries increasing amount of sediment.  Not only is sediment bad for the turbines at the generating section, far down stream, but it also increases the abrasiveness of the water in the Head Race Tunnel (HRT), wearing away the rock and concrete lining of the tunnel. During the August 2000 flood, sediment laden flood waters sand blasted the exposed dam sluiceway piers right down to the reinforcing steel, and actually wore down the nubs on the steel itself. On top of this, the soft waters of the Satluj River are normally fairly hard on concrete to begin with, and don't need assistance in wearing it down. 

The Nathpa Jhakri Hydroelectric Project therefore includes a large desilting works, consisting of four 500 metre long underground desilting chambers and the related intake works and network of connection tunnels, plus a silt flushing tunnel that returns silt from the collection hopper of each desilting chamber back to the river.

The desilting chambers are labelled at the top centre of the diagram, and are shaded in blue, along with the intake tunnels and the start of the head race tunnel. The Intakes are coloured green, just above the dam.

A diagram showing the four desilting chambers in section, along with the upper access tunnel, stairwell shafts, and access galleries. 

When I arrived in February 1999, the excavation of the desilting chambers themselves was well underway, as well as most of the connection tunnels. The intake works, on the other hand, were still being excavated and concrete work had not yet begun.

Inside Desilting Chamber #1, looking downstream. Excavation of a lift, or bench, continues in the far background. A Caterpillar front-end loader and workers can be seen in the foreground. The stair tower behind the loader leads to one of the maintenance and inspection access galleries that would provide personnel access to the chambers once they were commissioned and in service. Health and Safety procedures and regulations in India are not what I am used to in Canada, and I recall that climbing to the top of this stair tower was one of the scarier things that I did while I was on this job - mind you, I am afraid of heights, but I recall there there were no railings on the top level. The bottom of the chamber will eventually narrow out to a trough running the length of the chamber. The idea behind the Desilting Chamber was that the size of the chamber would allow the speed of the water flow to slow down enough that the silt and sand particles would settle out into the trough at the bottom, and be returned to the Satluj River via the Silt Flushing Tunnel (SFT). The clean water, with silt removed, would be siphoned off the top of the chamber and directed to the Head Race Tunnel (HRT) which would transport the water to the turbines at the powerhouse at Jhakri, 27 kilometres away.

The port in the background of this image leads to the stair tower seen in the previous photo, and is one of the access gallery manholes indicated on the schematic above. The port itself is a metal collar with bolts, cast into the concrete, which would be used to secure and seal the watertight hatch that would eventually be installed there. When the chambers are full of water, this gallery would be underwater. The stair shaft that provides access to this gallery from above is behind and to the right of the photographer. The stairs were not complete when I left the project in 2001.

This is the downstream bellmouth in Desilting Chamber #3 while under construction in April 2000. The formwork on the invert and walls is still in place here, and concrete work is progressing up towards the overt. Chamber excavation has not proceeded very far here, and the chamber will get much deeper - this bellmouth is located at the very top of Chamber #3. This is where clean water, with silt removed, would leave the chamber to head for the HRT.

Taken the same day as the previous image, but in Desilting Chamber #4, this bellmouth is slightly more advanced in construction with the walls pretty much complete. Only the overt form installation and concrete pour remain. The lift lines can clearly be seen in the concrete - 6 lifts and part of a 7th can be counted from the top of the current lift to the top of the concrete work. The outlet tunnel can be seen in the background through the bellmouth opening.

A manifold of four tunnels join the bellmouths at the downstream end of each chamber with the Head Race Tunnel (HRT).

The inside of the outlet tunnel from Desilting Chamber #4, looking in the opposite direction from the previous photo. The support towers and the ski jump concrete form for the overt pour are sitting in the tunnel waiting for installation. The HRT is behind the photographer in this photo.

A worker looks at a profiling platform in Outlet Tunnel #2. Once the mass tunnel excavation was finished, a work platform such as this would be run through the tunnel on rails to determine where the rock line was intruding into the tunnel profile, and workers could have a go at removing the protuberances with pneumatic hammers. This platform was also fitted with a steel tunnel profile that marked the minimum excavation line, but for some reason that item is not visible here - perhaps this was taken just as the platform was being assembled.

This photo was taken at the junction of Nathpa Adit and the start of the Head Race Tunnel (HRT), with the outlet tunnels and Desilting Chambers behind the photographer. The masonry wall to the left of the spotlights is right at the end of Nathpa Adit. Concete curbs have been installed along this portion of tunnel, and the HRT overt form is just visible in the background to the left of the two spotlights. The Chief Surveyor stands in the foreground, and appears to be carrying the tripod that I was using that day (though apparently not for this photo).

Excavation of the desilting chambers didn't always go smoothly. I've previously mentioned the poor rock conditions on this project, and the chambers suffered from this as well. There were at least two rock falls during my time on the project, and possibly more. The company brought in a consultant geologist from Canada to advise on how to better support the rock during construction, and the end result was a large number of cable anchors running from chamber to chamber through the rock pillars between each chamber, in order to better hold the rock together.

Chamber excavation was not without its challenges and dangers. Even though the rock was stabilized and reinforced with rock bolts and lined with shotcrete, rock falls such as this one were not an uncommon occurrence. The rock bolts can be seen sticking up out of the rock debris - failures like this occured when the depth of the failure plane exceeded the depth of the bolt penetration into the rock.

A rockfall, this time in Chamber #3, in May 2000. The workers in the frame give a sense of scale to the amount of rock that came tumbling into the chamber, and rock bolts can be seen both in the debris and sticking out of the exposed rock face. After further study by geologists, it was decided to drill through the common walls between chambers and install cable tension anchors between chambers to support the rock in those walls. This work was done after I left, and was hindered by the fact that the chambers had mostly been excavated to near full depth by the time it became apparent they were necessary.

Also ongoing during my time on the project was the excavation of the intakes and intake tunnels. 

The inlet tunnels brought water from the Intakes through to the Desilting Chambers (you can see pictures of the Intakes in the Surface Construction Gallery). One of the jeeps is parked in Inlet Tunnel #3, which has had its invert lined with concrete. The screed form that shaped the concrete would have run on the rails on each side of the tunnel. These rails would later be removed and replaced with new rails mounted right on the concrete invert, to be used by the overt form. A steel bulkhead is visible in the background at the entrance to the tunnel.

This is a rebar installation platform in Inlet Tunnel #1. The tunnel invert concrete has been placed, and the rails have been relocated from the position in the previous photo to the top of the invert concrete. The platform is riding on those rails. As seen here, workers on the various levels of the platform work to install reinforcing steel (rebar) around the circumference of the tunnel overt (crown) prior to the lining of the tunnel with concrete. If you look closely, you can see that one of the workers is actually climbing on the rebar cage between the rebar and the rock wall. My supervisor, the Chief Design Engineer, designed this platform and I was responsible for producing the production drawings that were sent to the steel fabrication shop.

At the upstream end of the intake tunnels was the intake works. The intakes were large concrete structures intended to direct water into the tunnels and desilting chambers with as little turbulence as possible. Up front was a trash rack of vertical fins, intended to prevent large floating debris from entering the system, followed by bellmouths to each tunnel. Very little of this work was completed when I left the project.

Plan view of the intakes showing the trash rack and bellmouths to intake tunnels 1 through 4.

I will leave the intakes themselves for a separate post.

Working in India: Anatomy of a Hydro Project - Diversion Tunnel (Part 6)

In a previous post, I presented photos taken during a period of construction on the 62.5m high gravity dam on the Nathpa Jhakri Hydroelectric Project on the Satluj River. At the end of the post, I asked the question: "How do you build a dam in the middle of a river in the mountains?" When you are a steep sided mountain valley, you can't just divert the water around the dam site - or can you? Well, you can - but it isn't easy. In our case, it required a diversion tunnel cut through the rock of the mountain side around the dam site on the right bank. The diversion tunnel was completed before I ever arrived on site, and was presumably plugged with concrete (or possibly just the steel gate at the upstream end) after I left.

After the diversion tunnel had been originally laid out, a rock slide at the intended inlet location meant that the tunnel had to be doubled in length. It had to be constructed on the right bank, so that it would not interfere with the construction of the desilting chambers and head race tunnel on the left bank. 

Layout of the dam area, with the diversion tunnel shown on the left side of the diagram.

When I arrived on the project in February 1999, the tunnel would already have been pressed into service for the winter months. The tunnel was only designed to handle up to a certain maximum flow (I don't remember what it was, but probably in the range of 200-500 cubic metres per second (cumecs), but the Satluj River varied between around 80 cumecs in winter to a normal maximum of around 2000 cumecs in the summer. In springtime, river flow rates from a nearby government monitoring station would be watched carefully, and as flows approached the tunnel maximum, flows would be removed from the tunnel and rerouted through the dam site. Dam construction would halt during the summer in areas below the water level. 

A close-up of the Diversion Tunnel (DT) inlet cofferdam (taken in September 1999), which forced the river to flow through the dam site. Summer flows were far too much for the DT to handle, and would cause significant damage if allowed to flow through the tunnel, so it would be blocked up for the summer so that maintenance could proceed. In August 2000, this cofferdam would be eroded away during a serious flood event, and the DT became filled with silt almost to the roof of the tunnel. The DT Bailey Bridge can be seen spanning the gap over the tunnel inlet. This bridge had a fairly limited load capacity, and this caused problems on several occasions. The cofferdam has clearly had traffic over it for some time, and was probably used to bypass the bridge for heavy loads, although I do not remember for sure at this point. A loader and two trucks have begun to dismantle the cofferdam.

A tight fit - one of the 17 tonne gate anchor girders arrives by truck across the DT Bailey Bridge. The bridge had to be realigned and beefed up especially to take this load, and even so, this photo shows the slight deformation of the bridge due to the weight. There was only inches to spare on either side as the girder crossed the bridge.

The next few photos show the sequence of removing the diversion tunnel cofferdam. The cofferdam would be removed in lifts (or layers) from top to bottom, until just one lift was left. The excavator then began removing the final lift from the upstream end, and moving to the downstream end, from where the cofferdam across the river itself would be started. 

In October 1999, the Diversion Tunnel inlet cofferdam is breached to allow the river to flow through the DT. Shown here, an excavator has removed the bulk of the cofferdam, and is about to breach the dam. Note the larger rip rap on the sides of the channel to prevent erosion.

Water is starting to make its way through the reduced cofferdam. A Hindustan 1025 off-road dumper is receiving material from the excavator.

The 1025 dumper is back to take more material. This material is stockpiled nearby, to provide a source of material to construct the upstream cofferdam that will prevent the river from flowing through the dam site.

The diverstion tunnel cofferdam is mostly removed, allowing flow through the tunnel for the 1999/2000 dam construction season.

Once the diversion tunnel cofferdam was removed, a new cofferdam was constructed across the river itself, to force the water to pass through the tunnel, and leave the dam site relatively dry.

An excavator starts to push off the upstream cofferdam that will block the river flows through the dam site.

Construction continues on the upstream cofferdam. A 1025 dumper and a dozer have joined the work.

In a somewhat precarious position, a dozer pushes material out to the end of the cofferdam, and is very close to closing the gap to the south bank.

The completed cofferdam, taken in March 2000. It has been in place since October 1999. Taken from upriver, the dam site is visible in the background.

With the cofferdam in place, the dam site would be excavated to clear sediment deposits from the summer season, and construction would resume. At some point in the spring, the river flows would increase once again, and the river would be allowed to flow through the dam once again, and the diversion tunnel would be blocked off for inspection and maintenance. The next series of photos show the tunnel interior in August 1999.

This photo was taken within the DT inlet during the August 1999, with the DT inlet cofferdam visible in the background. The river flows during the summer months were too much for the DT to handle, and would have caused damage to the tunnel lining, so the flows were removed from the tunnel and the summer months were used for maintenance purposes. You can see temporary stairs (made of sand bags) and a temporary ladder that were used to gain access to the tunnel floor.

Another view of the DT inlet, with the same access ladder from the previous image off to the right. To the left you can see the beginning of the concrete lining that was at the tunnel entrance. You can see that a considerable amount of water is leaking past the DT inlet cofferdam, and it was always advisable to have rubber boots (gumboots in the local parlance, and Wellingtons or Wellies in the parlance of my British-extracted supervisor) on hand.

This photo was taken with available light from the DT inlet, looking in the downstream direction. The Chief Design Engineer is walking further into the tunnel, right under the gate shaft for the DT inlet gate. The gate was lifted by mechanisms stored in a chamber accessible from the road above, although I never saw it used so I am not sure what the point of it was. Perhaps it was supposed to be used for the permanent closure of the tunnel after the dam was constructed, to avoid draining the reservoir, while still allowing the option of diverting the flows during the winter months for dam maintenance. The tunnel at this location was partly lined with concrete to prevent erosion from the turbulence at the tunnel entrance, but beyond the gate shaft the native rock was lined with shotcrete, a form of sprayable concrete.

A view further into the DT, about as far as you could go without a flashlight - the lighting here is from spotlights provided to aid the inspection and maintenance of the tunnel. The roof, sides, and floor of the tunnel are lined with shotcrete, and you can see a number of rock bolt heads sticking out of the tunnel roof. The rock in the Himalayas is fairly soft and of low quality, as rock goes, and has a high content of mica which is very soft indeed. This rock does not fare well when put in tension, and so long rock bolts were drilled and grouted into the rock face to provide additional strength and to try and prevent rock falls. You can see the channel worn in the tunnel floor from the water flow.

I have previously alluded to a large flood during August of 2000 that caused significant damage to the project works, and I will dedicate a future post to the post-flood damage assessment, but I will cover the affects to the diversion tunnel in this post. The flood consisted of an initial 12 metre high wall of water that swept down the river, and then a period of higher than normal river flows after the initial event. While miraculously not heavily damaged, the diversion tunnel was still affected - the inlet coffer dam was swept away, and a good portion of it (along with other river sediment and gravels) was deposited in the tunnel, filling it almost to the tunnel roof (or crown). As part of the recovery during the fall of 2000, the diversion tunnel had to be cleared out before it could be used again. This meant that a good portion of the 2000-2001 dam concreting season was lost.

Before I ever arrived on the project, the Diversion Tunnel had to be increased in length by a factor of 2, because a large rock slide occured at the location of the intended tunnel entrance. This slide remained unstable, and the flood in August 2000 reactivated a portion of the slide and wiped out a portion of the road. The Diversion Tunnel inlet can be seen near the top right of the photo, with the Bailey Bridge spanning it. The flood occurred in August 2000, while the DT Inlet cofferdam was in place to protect the tunnel from the summer flows. Unfortunately, the flood breached the cofferdam, washed it away, and a portion of the river flowed through the tunnel. The water velocity in the tunnel must have been much reduced, which served to allow the sand and silt carried by the water to settle out and fill the tunnel.

Work has begun in this photo on removing the debris from the Diversion Tunnel slide. Near the top left of the photo, you can see a Hindustan 1025 dumper and Tata Hitachi excavator working on clearing the top portion of the slide. This provides some idea of the scale involved here.

This is the outlet of the Diversion Tunnel, almost completely filled with silt, sand, and rocks after the flood breached the inlet cofferdam. This tunnel would have to be cleaned out before construction work could resume on the dam.

This, again, is the outlet to the Diversion Tunnel, but after the cleaning operation had begun. To the right are two workers, to give some perspective to the size of the tunnel. Lighting has been added to the tunnel in order to facilitate the cleaning operation. This lighting would not normally be present, and would be removed again before the tunnel could be used for its intended purpose.

This photo was likely taken just inside the DT outlet opening, showing the ribs intended to support the opening.

My boss walks ahead of me in the DT as we approach where the equipment is working to remove material from the tunnel. Wouldn't you like to be the worker assigned to make adjustments to the electrical panel on the metal stand situated in a large puddle of water?

After walking around the bend in the last photo, we approach the wheel loader as it works at the face of the silt deposit. The tunnel was fairly cramped for equipment, and this loader would have to turn around before it could deposit a bucket of silt into a truck. I'm assuming they either used a loader because it was the only one they had available, or because there wasn't enough room for an excavator to swing its boom. The tunnel would have originally been excavated using dedicated tunnel machinery, but a lot of that equipment was lost during the flood, with the remainder busy elsewhere. 

After the loader backs off to fill a truck, my boss climbs the silt face to see what lies ahead of the cleaning operation. This photo was taken on January 10, 2001, a few weeks before I left India for good, so I probably didn't see the tunnel fully cleaned out before I left.

The diversion tunnel was returned to service after I left the project in January 2001, although I am not sure if it was used at all until the fall of 2001. 

Knorr & Matthew

In an interesting coincidence, I saw two stories this week within a day of each other that took me back 19 years to a university work term at the Bedford Institute of Oceanography (BIO). I was lucky enough to be taken on by the Canadian Hydrographic Service (CHS) for the 1997 winter work term (and indeed one day a week for that summer), where I frequently had a view of the comings and goings from the BIO wharf. 

R/V Knorr at the BIO wharf in 1997.

One visitor during my time there was the R/V Knorr, a US Navy-owned research vessel operating out of the Woods Hole Oceanographic Institute, and the ship that discovered the wreck of the RMS Titanic. I was lucky enough to catch her during her departure from BIO, during light flurries. Launched in 1968, she was already 29 years old at the time, and she was still operating out of Woods Hole as late as 2014 or so. 

R/V Knorr departing from BIO in 1997.

Also at the wharf during some of my time at BIO was CCGS Matthew, a hydrographic vessel operated by CHS (she may still have been referred to as CSS Matthew at that time). She was at that time still in her all-white paint job, before the Canadian Coast Guard colours were applied. 

CCGS Matthew (left), CCGS Parizeau (right), with HMCS IROQUOIS photobombing in the background. All are now decommissioned or paid off (1997). None of the three ships are in CCGS or Navy service any longer.

Within a year or so of this photo, Matthew was repainted in the standard Canadian Coast Guard colours, and this is how she appears in most of the photos that I have of her. A few from my collection:

CCGS Matthew in 2005.

CCGS Matthew in 2008.

CCGS Matthew in 2012.

This last photo is probably the most recent that I have of her (underway at least), as she was laid up in 2012 due to budget cuts. Shipfax is now reporting that she has been renamed 2015-03, and is being readied for disposal. Built only in 1990, at 26 years of age she should have some life left in her, but alas, not in Canadian government service. 

R/V Knorr has 20 years on Matthew (errr, I mean 2015-03), but instead of being scrapped, is being renamed ARM RIO TECOLUTLA and is being transferred to the Mexican Navy. Perhaps someone will find some use for Matthew, though perhaps her singular design as a hydrographic survey ship will count against her. I was told that she rolled quite badly when her two survey boats were not embarked, but perhaps the aft deck could be closed in and some ballast added.

Working in India: Anatomy of a Hydro Project - Dam (Part 5)

Having shown some of the scenery I photographed while in India, I should probably cover the reason that I was in India in the first place: the construction of the Nathpa Jhakri Hydroelectric Project. The project consisted of many parts, the major portions being as follows:

1. a 62.5 metre (~205 foot) high concrete gravity dam at Nathpa, on the Satluj River;
2. concrete intake works and tunnels;
3. four 500 metre long underground desilting chambers;
4. 27 kilometres of head race tunnel (HRT), running from Nathpa to Jhakri;
5. a 1500 MW (megawatt) powerhouse at Jhakri with six 250 MW turbines.

Of the above, 11km of #4 and all of #5 were on a different contract - the Continental Foundation Joint Venture (CFJV) I was working for was handling the remainder. On top of the list above, there was also a significant number of temporary works (bridges, shops, roads, etc) that were also the responsibility of the contractors, and which we were responsible for designing.

An overview of the dam site (looking west), with the upstream coffer dam just visible in the bottom half of the photo, just above the grassy foreground slope. Looking downstream, the bank on the left is the Left Bank and the bank on the right is the Right Bank. Simple. The diversion tunnel inlet is just out of site to the right of the upstream cofferdam. This photo was taken on April 27, 2000. The Satluj River can go anywhere from 50-80 cumecs (cubic metres per second) of flow in the winter months, all the way up to 2000 or more cumecs in the height of summer when snowmelt is at its greatest. During the summer, dam construction would halt, and the upstream cofferdam would be dismantled to allow the river to flow right through the dam site.

There are two main types of concrete dam: gravity and arch. The latter is kind of like a bridge arch on its side, with the top of the arch pointing upstream, and the bridge abutments braced against the side of the valley or gorge in which it is built (think Hoover Dam). We were building the former - a 62.5m high concrete gravity dam, intended to hold back the weight of the water through sheer weight of concrete and friction with the bedrock on which it is built. 

Another aerial view of the site at Nathpa. The concrete structures just left of centre are the intakes and the crane platforms built above them. To the right, barely visible, is the concrete structure of the dam slowly coming out of the ground. A bridge and several groups of workshops can be seen downstream, towards the top right of the image. The road running along the top left of the image is National Highway 22. The traveling end of the cable crane can be seen just below the highway, but up the slope from the intakes.

A schematic layout of the dam and intakes area. Top is upstream, bottom is downstream. The orange coloured "Adits" are access tunnels, some of which would have been filled in after construction. The Head Race Tunnel (HRT) leaves the sketch to the right, while the Flushing Tunnel returned silt to the river itself.

The dam creates a reservoir of water in the river, which enters the intakes and desilting complex, then makes its way through the headrace tunnel to the powerhouse 27km away. This creates 428 metres (1400 ft) of hydraulic head to turn the turbines, which produce electricity. Therefore, the dam needs to hold water back - it can't let water go through or around it, the water must pass through the intakes (unless deliberately allowed to spill over the dam through the spillways). 

Bedrock laid bare downstream of the dam - this area is called the apron, and was filled with concrete.

In order to ensure the dam is watertight, construction began by excavating away the riverbed until bedrock was reached. The bedrock in the Himalayas isn't the best quality, as it is fairly young rock, and it has a lot of cracks - those cracks were filled by injecting cementitious grout into the bedrock. Tunnels were excavated into the valley walls on either side of the dam so that a grout curtain could be made around and under the dam. Basically, any water that wants to push its way past the dam must do so by infiltrating cracks in the rock all the way around the outside influence of the grout curtain, and then back through cracks until it reaches the river valley again. The volume of water making this journey should be very small indeed. 

Workers in one of the grouting galleries on the side of the dam.

Once the bedrock had been uncovered and the cracks grouted, the dam concrete itself could start to be placed. The dam is made up of 11 blocks across its width, with only the centre blocks going the full depth of the reservoir - the wing blocks on the sides are a fair ways up the valley walls and are cast into a notch cut into the rock. I can't recall exactly, but I think each block was about 15m wide, and this was limited to allow expansion joints to be placed between each block to minimize cracking of the concrete. In addition, each block was poured in 1.5m deep lifts. The curing of concrete is a chemical reaction, and monolithic concrete pours create "heat of hydration" during the curing process. If you pour too big a block of concrete at one time, the heat created by the curing reaction will actually cause the surrounding bedrock and concrete to crack. Cracks in a dam are bad.

A concrete pour proceeds on a lower lift in a dam block, probably Block 4. The blocks proceeded in a staggered fashion, partly for scheduling purposes (to allow freshly poured concrete to cure) and the need to have some blocks above the summer flood levels, and partly to allow better dispersal of the heat generated by curing concrete (called heat of hydration). Each dam block was poured in Lifts of 1.5m in height, although some early lifts were poured in 0.75m half lifts due to concerns about cracking of the bedrock from heating. The concrete is dropped to the dam via a concrete bucket suspended by a cable crane that runs across the valley; the concrete buckets are supplied with concrete by trucks that deliver concrete to the loading dock high on the right bank. As shown here, the concrete lift is poured in three layers that advance from the downstream end to the upstream end of the dam. In Block 3 to the left, you can see the climbing forms that hold the concrete within the block during a pour. Once the pour is complete and the concrete has cured sufficiently, the forms are removed and are lifted up for the next pour. Block 4 only needs forms at the upstream and downstream ends because the rest of the poured concrete is confined by the neighbouring dam blocks.

A concrete pour proceeding, probably in Block 4. CFJV stands for Continental Foundation Joint Venture, made up of Continental Construction Limited (CCL) and the Foundation Company of Canada (FCC). The latter was my employer at the time, but by this time only operated in India under this name - back in Canada it was called BFC Civil, and has since been renamed again to AECON. 

Concrete was batched at a plant nearby, and trucked to a platform from which it was dumped into the concrete bucket in the photo above. The distance was so short, hopper trucks (instead of the mixer trucks one is accustomed to seeing) were used, and they could dump their concrete very quickly into the bucket. A cable crane spanning the river valley would pick up the bucket and dump it in the dam block being poured. 

To keep water from forcing its way between each dam block, a total of three different kinds of waterstop were placed at the front of each joint: one copper, one PVC, and one a bituminous substance that was poured into a diamond shaped groove formed between blocks. 

The three waterstops between dam blocks, probably Block 8 and Block 9, start at the base of the following block. In this case, Block 9 will start from this elevation and head upwards. In the previous pour, the two blocks were being poured monolithically. The copper waterstop is furthest upstream, the PVC (rubber) waterstop is furthest downstream, and there is a gap left in between the two into which liquid asphalt or similar substance is poured after the concrete pour. Three separate and different waterstops were used on each joint to provide redundancy.

The concrete pour continues at the upstream end of Block 4. The various waterstops (3 in total) can be seen cast into the front edge of Block 5. These waterstops prevent water from infiltrating along the construction joint between each dam block. The dam is poured in multiple blocks with construction joints between each block to reduce cracking of the concrete. The rebar over the gallery and stairs from Photo 19 can be seen to the bottom left of the photo. The exposed end of a mid-height gallery is visible in the side of Block 5 - I seem to recall that there were at least 3 levels, if not 4, of galleries in the dam. Each gallery is used to check for leakage in various parts of the dam, and to provide access to strain gauges that are incorporated into the dam to record stresses within the structure. The various galleries continue into the rock at each end of the dam on the left and right banks.

After a lift was poured in any given block, the concrete was allowed to cure. A scum would form on top of the curing concrete, which would be removed through high pressure water - a process called "green cutting". This would expose the aggregate (rock) on the top of the lift of concrete, which would allow the subsequent lift of concrete to bond better to the lift below. While a block was curing, the blocks on either side of it might be poured, to keep work going. The dam was poured in such a way as to keep one block several lifts ahead of the block behind it, partly so that the formwork of the leading block did not interfere with the lagging block. 

In this manner, the dam was slowly poured to its full 62.5m height. The five central blocks contain the spillways: Block 6 had the central spillway, with two smaller spillways on either side in Blocks 4 & 5 and Blocks 7 & 8. The spillways contained large steel gates that would normally be kept closed in winter, but could be lifted up in spring, summer, and fall to allow water to pass and regulate the level of the reservoir. 

Standing in the Block 7 sluiceway bucket area and looking up at the piers of Blocks 7 and 8. You can see the parabolic shape of the sluiceway in Block 8 taking shape here, between the two piers to the left. The inset portion of the side wall of the sluiceway is meant for the sluiceway liner, which was high-density concrete in some dam blocks and high strength steel in others. The Satluj River runs full of sediment in the summer months, due to the soft rock in the Himalayas, and the combination of fast flowing water and sediment is the equivalent of sandblasting to concrete. Add to this soft mountain water that eats concrete, and you need resistant liners for the sluiceways to prevent the concrete from being eaten away. The right bank loading dock can be seen at the top left of the image.

During my time on the project, none of the gates themselves were installed. Only two of the gate girders that would support the gates were installed, and one of those was washed away in a flood. 

A crawler crane places one of the 18-tonne gate girders in place on the right pier of Block 8. There are two of these girders for each of the sluiceway blocks. Two girders would be installed before a large flood occurred in August 2000, during which the left girder in Block 8 (not the one shown) would disappear and not be seen again for another year or so.

The two gate girders are now placed in Block 8 - the left girder would go missing in a flood in August 2000, ripped from its housing and buried in silt and sediment. I never saw it again, as I returned to Canada before it was found.

Behind the sluice buckets and dam structure is the concrete apron, constructed to protect the bedrock from the water flowing through the sluiceways from erosion that could undermine the downstream end of the dam. 

Excavation in the apron area. 

Excavation work on the dam didn't always go smoothly, especially if a pump failed.

Excavation in the apron area. One of the construction superintendents inspects the results of a pump that failed during the night shift. Workers were present when it happened, but for whatever reason were unable to find a replacement before the excavation flooded. The excavator from the previous photo can be seen sticking out of the water. Due to the steep sides of the excavation, the machine could not be removed without the use of a crane, which was apparently not available. The side of the excavation was turned into a ramp, and after the water was pumped out, an operator clawed the machine out of the hole after which it was overhauled by mechanics.

The apron area was excavated down to bedrock, and a pattern of reinforcing steel dowels were drilled into the rock, and a cage of reinforcing steel was constructed and anchored to the dowels. The whole area was later filled with concrete in blocks, similar to the dam itself.

Workers empty a concrete bucket in the apron area behind the main dam. They are pouring a leveling slab directly onto bare bedrock here. If you look closely, you can see the well worn surface of bedrock that has been subjected to the flow of water. The concrete to the right is the back wall of the sluice bucket section of the dam. The sluice bucket will cause water passing through the sluiceways to jump into the air at the back of the dam, and if it were to crash down on the rock behind the dam it would erode the rock away and eventually undermine the back side of the dam. Thus, a concrete apron is poured at this location to protect the rock. The 1435 painted on the dam, with the line next to it, represents an elevation above sea level (i.e. 1435 metres) as well as the top of the concrete apron at this location.

The concrete apron behind the dam follows the contours of the bedrock. The first task is to drill and grout in anchors of reinforcing steel, to prevent the apron from separating from the bedrock. This part of the apron is being infilled between two completed portions. I was responsible for laying out the anchor locations prior to them being drilled in the field.

Since the previous photo was taken, the anchor installation has been completed, formwork has been added to the downstream face of the pour area, and the rebar mat that will reinforce the exposed face of concrete has been installed (as detailed by yours truly).

Concrete is now being poured into this portion of the apron. The pour is staggered in lifts, and although the fresh concrete has not yet reached the upstream end, workers have already begun to finish the concrete surface at the downstream end.

The concrete apron follows the contours of the bedrock behind the dam, and here you can see the shape of the reinforcing steel echoing the shape of the rock. One of my jobs was to detail the steel in this area, and send the details to the steel fabrication yard for cutting and bending.

One of the more impressive pieces of temporary infrastructure built to construct the dam was the cable crane over the dam site. 

This view takes in both the tail tower (foreground) and the right bank anchor point (background). The next photo shows a closeup of this view.

With the cable reel on the (left bank) traveling unit in the upper right of the image, this photo looks all the way across the valley to the right bank anchor point (look in the upper middle of the photo). The traveler head can be seen on the cable near the centre of the image - this unit traveled back and forth across the valley, and the crane hook would rise and lower below the traveler.

Another view of the cable crane's traversing unit. The large wheel shown here is a reel for the power and control cables. The traverse speed along the track was quite slow, and so it was best if the traversing unit could be lined up with both the area of the dam being worked on and a portion of the loading dock on the right bank where concrete hopper trucks could dump concrete into the concrete bucket. Sometimes the cable would not intersect the loading dock, and the speed of a concrete pour would be severely curtailed as the traversing unit would have to go back and forth each time. When this happened, it was preferred to have a crawler crane carry out the pour.

The Cable Crane tail tower sits on the rails near the trestle. The trestle was constructed later than the rest of the track, once construction on the dam required more coverage area from the crane.

This photo was taken while riding on a platform hung from the Cable Crane, looking straight up. Talk about vertigo! I seem to recall that I wasn't very happy taking this photo, as I am not terribly fond of heights, and looking straight up while having a drop of several hundred feet below just doesn't do anything for me.

While the overall project ran from 1993 to 2004, I was only assigned to the project for two years from 1999 to 2001. As such, I wasn't able to photograph the final stages of dam construction. I will end this post with a photo taken in the concrete apron area, showing some of the people I worked with on this project. 

A number of CFJV employees stand on the bedrock in Block 11 prior to concrete being poured. To the right of the photo you can see the painted line that represented the divider between Blocks 10 and 11. Top left employee is a senior superintendent from British Columbia, while the man immediately right of him is the Chief Design Engineer (my boss at the time).

So, how do you build a dam in the middle of a flowing river? You don't. My next post on this project will cover the diversion of the river around the dam site.