Nuozadu: A milestone project of China's earth-rock dam

Catching up with the 10th anniversary of the power station's commissioning

It was autumn, and we took a train from Kunming to Pu'er. The vegetation was visibly lush outside the window. Although Yunnan is known as the Kingdom of Plants and the South of Colorful Clouds, it must be said that Pu'er and Xishuangbanna in the lower reaches of the Lancang River are the best. As far as the eye can see, the blue sky seems to have been washed by water, and the color of the soil cannot be seen in the mountains and forests. Even in the city, flowers, plants and trees are the absolute protagonists. After leaving Pu'er Railway Station, I had the illusion of traveling on vacation. The primitive emotions of returning to nature were ignited in our bodies, and we gradually became joyful. Unexpectedly, at the Nuozadu Hydropower Station, every power plant employee had the same joyful expression on his face. At meal time, the cafeteria was full, and everyone was whispering while eating, and the joyful mood was filled in the air. I immediately "detected" that "something was going on". It turned out that two days later was the tenth anniversary of the power generation of the first unit of the power station. The power plant employees had warmed up in advance and held various sports competitions. In the past few days, most of the employees have gathered at the power plant to welcome the arrival of September 6, 2022, the 10th anniversary of the Nuozhadu Hydropower Station. We just happened to catch such a grand event.

Nuozhadu Hydropower Station

Nuozadu Hydropower Station is located on the lower reaches of the Lancang River at the junction of Simao District, Pu'er City, Yunnan Province and Lancang County. It is the largest hydropower project on the Lancang River, with a total installed capacity of 5.85 million kilowatts, a guaranteed output of 2,506 megawatts, and a designed average annual power generation of 23.912 billion kilowatt-hours. The project is mainly for power generation, and has comprehensive benefits such as flood control, improvement of downstream shipping, irrigation, fisheries, tourism and environmental protection.

The Nuozhadu Hydropower Station project is huge in scale and has outstanding innovative achievements. It has provided valuable experience for the construction, quality control, operation management and formulation of normative standards for 300-meter-class core rockfill dams in my country. It is a milestone project for ultra-high earth-rock dams in China and even in Asia.

Where the Heroes Crossed the River

At the first stop, we finally saw the gravel-soil core wall rockfill dam of Nuozadu.

Before I came here, I was always confused. The first decade of the 21st century was a period of comprehensive and rapid development of my country's water conservancy and hydropower industry, and it was also the golden decade for the technological progress of my country's reservoir dam construction. Why did the Nuozadu Hydropower Station, which was started during this period, choose a very traditional earth-rock dam instead of the more common concrete dam type of this period? Moreover, as far as earth-rock dam construction is concerned, the current domestic specifications are only applicable to dams within 200 meters, while the height of Nuozadu's dam reaches 261.5 meters. From the perspective of the domestic and foreign hydropower industries, there is not much experience to learn from for 300-meter-level earth-rock dams. For such a large-scale earth-rock dam, once the scale of the project becomes larger, its construction difficulty will change from quantitative change to qualitative change, and increase in geometric progression.

After arriving at the site, the mystery was finally solved. The rushing Lancang River reaches Nuozadu, and the mountain suddenly narrows, forming a "small waist". Nuozadu is a Lahu language, and the corresponding Chinese meaning is the place where heroes cross the river. It can be seen that the water here is turbulent and the terrain is steep. But such a terrain is just suitable for building a hydropower station. Not only is the terrain good, but the geological conditions of Nuozadu are also relatively perfect. The rock strata distributed in the dam site area mainly include granite and sandstone strata. The dam foundation is mainly granite with a single rock type. Sandstone is mainly distributed on the platform above the left bank dam top. The riverbed and left bank of the dam site are shallowly weathered, the faults are small and few, and the rock integrity is good. Only the structural weak rock belt on the right bank of the dam foundation is large in scale, and it runs parallel to the bank slope and tends to be inward of the slope. The engineering properties are poor, which is one of the main engineering geological problems of the Nuozadu Hydropower Station. Therefore, after comprehensive comparison, the power station builders chose a core wall rockfill dam type that can better adapt to the engineering geological conditions of the dam foundation and has a relatively simple foundation treatment project.

Nuozadu Project Hub Area

The Nuozhadu Reservoir is particularly beautiful after the water storage. Unlike other reservoirs that form a flat lake like a mirror after the water storage, the Lancang River here has winds and waves. When the weather is fine, the waves are small, and the sunlight is scattered on the water like broken gold, and is pushed to the shore by small waves; when it rains, the waves are big, and the speedboat we are riding is swayed from side to side. The sky in September is like a child's face. We took a boat to view the reservoir in the drizzle. When we got off the boat, it was "neither windy nor sunny." However, I was pleasantly surprised to find that the color of the water had changed, from the light green just now to light blue. The staff told me that the water here changes 12 colors a year. It not only changes with the weather and seasons, but also has different colors at different times and angles. "But the water quality here meets the second-class drinking water quality standards. The change should be due to external factors."

The broad and majestic dam

Nuozadu Hydropower Station was planned in 2004, the first unit started generating electricity in 2012, and all units were put into operation in 2014. It is the main power source for "West-to-East Power Transmission" and "Yunnan Power Transmission". The power station hub project consists of a gravel-soil core wall rockfill dam, an open spillway and energy dissipation pond on the left bank, a flood discharge tunnel on each of the left and right banks, a left bank drinking water power generation system and ground auxiliary plant, a line field, and downstream bank protection projects. The entire dam hub area is like a beautiful big garden. The staff "complained" to us that the grass and trees here are growing wildly. The grass and flower beds that had just been trimmed for a few days were restored to their original state after a rain, not to mention the wild animals that appeared on the road in a swaggering manner, completely treating themselves as the masters of this place. We heard some "Versailles" meanings from it, but we have to admit that the natural environment here is indeed like a fairyland on earth.

A zigzag road was built on the dam surface, or rather, a series of zigzags. From the top of the dam to the bottom of the dam, a wide two-way carriageway meandered down. We drove through it, which was very novel. Compared with concrete dams, Nuozadu is particularly solid and broad, making humans close to it look as small as ants. But such a huge project is most afraid of the erosion of termites. "A thousand-mile embankment is ashamed of ant holes." In an exhibition hall of Nuozadu, I saw a termite nest more than one meter high dug near the power station. The dense holes made people feel claustrophobic. Fortunately, Nuozadu Hydropower Station has established an integrated earth-rock dam termite prevention and control system that integrates "luring, killing, and controlling". It has successfully reduced the ant infestation rate in the hub area of ​​the power station to below 0.97, and the ant infestation rate in the prohibited area has always remained at 0%. It has obtained many patents and awards, ensuring the safe operation of the project.

Beautiful Nuozadu Hydropower Station

The Nuozhadu gravel-soil core rockfill dam has a crest elevation of 821.5 meters, the lowest foundation surface of the core wall is 560 meters, and the maximum dam height is 261.5 meters. The crest width is 18 meters, the upstream dam slope is 1:1.9, and the downstream dam slope is 1:1.8. The center of the dam is a vertical core wall, and the two sides of the core wall are filter layers. Outside the filter layer is the rockfill dam shell. From the outside, we can only see the densely packed stones on the dam surface. "You can imagine that the innermost core wall has the finest and least stones, and the stones are coarser and more as you go out." The staff explained this, and the cross-section of the dam unfolded vividly in front of us.

The open spillway is arranged on the shore side of the left bank platform in a straight line, using diversion and energy dissipation ponds to dissipate energy. The energy dissipation pond adopts a lining form with revetment but no bottom protection. Looking at the scene, the open spillway is like a giant slide. The total horizontal length from the channel to the end of the energy dissipation pond is 1,445 meters and the width is 151 meters. We asked the staff on the spot why the energy dissipation pond has revetment but no bottom protection? Will the huge torrent rushing down from the top wash out a big pit at the bottom of the energy dissipation pond? "The bottom of the energy dissipation pond is originally hard granite, and a new structural form of the boundary bottom plate of the energy dissipation pond revetment is adopted, which can protect the bottom plate of the energy dissipation pond from being damaged, so concrete lining is not needed. The revetment is to prevent the flood from the energy dissipation pond from eroding the vegetation and soil on both sides." The staff introduced to us carefully, "However, this spillway was built to deal with extremely large floods. It has not been used yet. It was only used once during an experiment."

The red clay core material of Nuozhadu

The main engineering materials of Nuozadu are locally sourced. There is a rich red soil here, which is highly viscous and dense, making it very suitable as the raw material for the core wall. In order to make full use of the excavated materials from the project as dam filling materials and reduce the amount of supplementary mining in the material field, not only the core wall materials, but also the rockfill materials, filter materials, contact clay and slope protection stones are given priority. According to statistics, the total amount of earthwork excavation for the main buildings of the Nuozadu project is about 5345.66*104 cubic meters, and the total amount of dam filling is 3268.42*104 cubic meters. The backfill rate reaches more than half. This "recycling and reuse" method not only minimizes the impact on the environment, but also saves costs and shortens the construction period.

On the top of a mountain, watching the river rushing

Nuozhadu Reservoir

It was the first time I saw such a broad and majestic dam. Sports cars could even run on the dam surface. It was hard to imagine how this huge structure was built. The staff told us that Nuozadu was the highest earth-rock dam in Asia at that time, about 100 meters higher than the Xiaolangdi and Pubugou projects built before. There was a lack of ready-made experience for reference during the construction process, and it was urgently necessary to study a complete set of dam-building technologies for super-high core rockfill dams over 260 meters high under the conditions of "high head, large volume, and large deformation".

The Nuozhadu Hydropower Station is the first 300-meter core rockfill dam built in China. It is a world-class milestone project that exceeds standards and experience, and every step is taken by trial and error.

As far as the dam is concerned, as the dam height increases, the dam body settlement deformation increases rapidly, and deformation control becomes increasingly difficult. As the highest earth-rock dam in China at that time, the natural soil of Nuozadu could not meet the demand for usage. Construction personnel and experts proposed a solution of adding artificial crushed stone anti-seepage soil, and through indoor and large-scale field test research, determined the economically reasonable addition ratio (35%) that meets the deformation requirements, and formulated appropriate design index parameter requirements such as anti-seepage and mechanics. This move is unprecedented in previous earth-rock dams. Everyone subconsciously believes that the anti-seepage function of the earth core wall mixed with stones will definitely be greatly reduced, but experimental data show that after using artificial crushed stone anti-seepage soil, the compression modulus of the core wall soil material increases by nearly one-fold, which greatly reduces the settlement deformation of the dam body, and the anti-seepage performance is also very good. According to the monitoring data after the completion of the dam, the actual deformation and seepage indicators of the dam are far better than similar projects at home and abroad.

Construction scene of Nuozadu Dam

The builders also pioneered a method of mixing flat paving and vertical mining, as well as the appropriate thickness of soil and stone paving layers and specific mixing processes; developed a 600 mm diameter super-large compactor, and conducted relevant comparative analysis with the equivalent substitution method, and determined a 152 mm three-point rapid compaction method for rapid testing of the quality of core wall gravel-mixed soil filling, which improved the testing efficiency. For the first time, a set of technologies for the design, construction process, and quality control of artificial crushed stone and gravel anti-seepage soil were systematically proposed.

Today, Nuozadu, the record of the highest earth-rock dam in China, has been broken by the Lianghekou Hydropower Station on the Yalong River, which will be put into operation in 2021. The maximum dam height of the Lianghekou Hydropower Station is 295 meters. Although as a local material dam, each earth-rock dam has unique external environmental constraints such as topography, geology, hydrology and meteorology, and dam material sources, and its engineering difficulties are also different, Nuozadu Power Station, as the first 300-meter-class ultra-high earth core wall rockfill dam built in China, still leaves a lot of valuable experience for later generations. And China's dam-building technology has finally reached the top of the world after countless explorations and countless climbs on the shoulders of giants.

Only at the top of the mountain can you see the rushing river; above the peaks, you can feel the mighty wind.

Earth-rock dams are not “earth” at all

Since the filling materials are stones, clay and other materials, the earth-rock dam is generally considered to be very "rustic". Compared with concrete dams, earth-rock dams are huge in size, appear rough and bold, and give people the impression of "not enough technology". However, when you go to Nuozhadu, you will find that the earth-rock dam is not only not rustic, but also technological and environmentally friendly.

During the construction of the Nuozhadu Project, the builders not only conducted systematic and in-depth research on the characteristics, calculation and analysis methods, dam structure, seismic measures, construction technology and quality control standards of the ultra-high core wall rockfill dam, and solved the key technical problems that restricted the construction of the ultra-high core wall rockfill dam, but also successfully developed the "digital dam" system for the first time, realizing real-time and online monitoring of the entire process of dam material source, quality, construction technology and methods, ensuring the excellent construction quality of the dam. It is a major innovation in the world's dam construction quality control technology.

For the ancillary buildings other than the dam, the builders proposed a new structural form of the moving boundary bottom plate of the energy dissipation pond revetment, which not only reduced the concrete volume of the bottom plate by 161,000 cubic meters and reduced the construction difficulty, but also greatly reduced the risk of damage to the bottom plate of the energy dissipation pond and improved operational safety. They developed and built a new type of water inlet with stacked beam gates and stratified water intake, which effectively controlled the downstream water temperature and created good conditions for fish reproduction.

Nuozhadu underground powerhouse excavation period

The underground main and auxiliary powerhouses are built in the mountain on the left bank, with a total length of 418 meters, a maximum span of 31 meters, and a maximum height of 81.6 meters. They are equipped with 9 generators with a single unit capacity of 650,000 kilowatts. The tailwater surge chamber is cylindrical, with a total of 3 tailwater tunnels. The three units share one surge chamber and one tailwater tunnel. The Nuozadu underground water diversion power generation system is huge in scale, consisting of 140 underground caverns. The mountain where the underground powerhouse is located is entirely made of hard granite, making excavation very difficult. "Other people who dig holes are afraid of bad geological conditions and easy landslides, and they need all kinds of support and anchoring. Our geological conditions are too good, but we are also worried. We can't dig. It's too hard and too big." The staff began to "complain" to us with a smile, "In order to arrange facilities such as the line outlet factory, half of the mountain has been leveled. It's a granite mountain." No wonder the top of the underground powerhouse looks like a flat small garden. We once looked down at the bottomless line outlet from above, and did not realize that this was actually a high mountain. It was one of the two mountains that "pinched" the Lancang River into a small waist to create conditions for the construction of the Nuozadu Power Station. It was really disrespectful.

Nuozhadu underground factory

After the Nuozhadu project was completed and put into operation, the power station's production and operation insisted on the path of intelligent development, and worked hard to explore a new production management model of "condition inspection, integrated operation and maintenance, and unmanned duty". Finally, on the 8th anniversary of the first unit's commissioning, at 9:06:06 on September 6, 2020, unmanned duty was officially implemented.

The unmanned mode is an advanced stage of reform and development in the duty mode of modern giant hydropower plants. It is not a simple withdrawal of operating personnel from the central control room, but a complex system engineering involving the quality of power plant personnel, ideological concepts, automation level of power plant unit equipment, emergency response capabilities and operation management mechanisms. It is the only way to create a world-class hydropower plant and build a smart power plant.

The Wizard of Oz painted with ecological background

Returning to the power plant production management camp from the power plant hub area is like walking into a fairy tale world of The Wizard of Oz, with small bridges, flowing water, pavilions and terraces hidden among the tall trees, and guavas and mangoes hanging on the trees exuding a sweet scent.

Mango tree behind the campsite

The Dazhong River runs through the middle of the camp. In summer, the lotus fragrance is everywhere. In autumn, only the remaining lotus leaves and the fat lotus pods are left in the river. Some are vividly green and full, while others have dried up into artistic shapes. The most common plants in the camp are various bananas and iron trees. They all have broad leaves and straight trunks, which makes it difficult to tell them apart until the staff took us to the rare plant garden.

Cycas comb-tooth

The rare plant garden is built in the factory camp, covering an area of ​​about 100 mu, including 40 mu of rare plant protection area, 10 mu of precious plant park, 15 mu of nursery area, and 35 mu of rare vegetation cultivation area. It mainly transplants two national first-class protected plants, Cycas cycads and Cycas comb-toothed, distributed in the hub area and the reservoir inundation area, and nine national second-class protected plants such as Oryza verruca, Dogwood, Alsophila spinulosa, Cycas ferns, Syngonium, Terminalia Thousand Fruits, Menglun Wing Tree, Dalbergia nigra, Toona redus, Fagopyrum goldenensis and other precious plants and communities. At first, we passed by the roadside of the camp many times, and we only felt that all kinds of plants were full of vitality and growing very well. There were also wooden signs with introductions about them, but we didn't realize that this was a rare plant garden. The staff carefully introduced Cycas cycads and Cycas comb-toothed, which are the most common plants we see in the camp. They are the only two national first-class protected plants here, and they are indeed highly ornamental.

Oryza verruca

There are 9 species of second-level protected plants. "This is Oryza vulgaris. The small grains are its seeds. Although it looks like a weed, it is one of the mother species of hybrid rice and is very old." The staff introduced their identities and growth to us one by one. "This is Dracaena parviflora. It was discovered by the late Professor Cai Xitao of Xishuangbanna Botanical Garden in Yunnan Province in order to find a substitute for the quick hemostatic drug for gunshot wounds. It also has high ornamental value."

Dracaena microphylla

I joked that this rare botanical garden was well built. It can not only be used for employees to enjoy daily, but also popularize knowledge about rare plants. The staff said that their camp not only has a botanical garden, but also a "zoo" and a fish breeding station. We walked to see it. We thought that the fish breeding station in the camp would be very small, but we didn't expect that there were more than 20 open-air pools of various sizes. There were signs on the walls of the pools with various difficult names such as "giant bream", "Chinese knife catfish", "fork-tailed catfish", "Chinese knot fish", etc. In the past ten years, Nuozadu has made continuous breakthroughs in the artificial breeding technology of fish, and has successively achieved the artificial breeding of giant bream and Chinese knot fish, and the artificial domestication of Chinese knife catfish, with 40,000 to 80,000 fry artificially propagated each year. The giant bream was successfully bred artificially for the first time in China, setting the world's first record for artificial breeding of catfish.

Fish breeding station

So far, the power station has organized 29 artificial propagation and release activities, releasing 386,200 fry of forktail catfish, giant catfish, Chinese knot fish, etc. In order to promote gene exchange between upstream and downstream fish, Nuozhadu Power Station conducts net fishing across the dam every spring and autumn, catching and releasing more than 100,000 Chinese knot fish, Yunnan four-barbed barb, long-hipped catfish, Chinese catfish and other fish, making positive contributions to optimizing the community structure of the Lancang River and protecting fish resources and biodiversity.

Fish enhancement and release in Nuozhadu reservoir area

Meet "Big Bear and Little Bear"

Not far from the fish breeding station is the wildlife rescue station, which is jokingly called the "zoo" that employees can see without leaving home. It is the first wildlife rescue station in the country invested, built, operated and managed by a hydropower enterprise.

Overlooking the Wildlife Rescue Station

The sun was shining brightly on the day we went there, and many animals were basking in the sun in the yard. Yes, each animal has its own room and small yard, and the yards are closely connected and neatly distributed on both sides of the road. The keeper led us through them, just like walking in a large "residential" alley. At the entrance of the alley lived a tribe of monkeys, "Look at this monkey with a black hat on its head, they are capuchins. These monkeys were sent here by local villagers because they were injured." The keeper said that in a month or two, when they recover from their injuries, they will be released into the wild.

Wildlife rescue station releases monkeys

Ten years ago, the Wildlife Rescue Station was only used to collect, rescue, temporarily raise and release wild animals affected by construction and water storage. In the past ten years, the Animal Rescue Station has expanded its animal rescue and protection scope to the entire Pu'er City as a rare animal rescue station and rare animal breeding center of the Pu'er Forestry Bureau.

"Some animals that were injured or separated from the group and could not meet the conditions for release after rescue were settled here." We saw many animals here, including vultures, white pheasants, cobras, wild boars, black bears, concave-shelled tortoises, peacocks, Indian bison, etc. "This vulture was injured and fell behind, so we made it fat. It can't even fly. It needs to eat two kilograms of lean meat every day, and it won't eat fat meat." The keeper knows every animal here very well. "Why don't you let it lose weight before releasing it?" We began to ask questions out of curiosity. "It's separated from the group, so it won't survive if released." "Doesn't it eat carrion?" "Vultures just don't eat live animals. Doesn't fresh meat taste better?" We laughed out loud.

Fat vulture

At the "end of the alley", we saw three black bears. When they stood up, they were more than a person tall, which was very intimidating. Two of them lived together, and the other one lived alone. I asked the keeper why the black bears were treated specially and lived separately, since other animals lived together in the same clan. "These two caged together are siblings. The other one is not from the same clan, and they will fight if they are caged together. Bears fight fiercely, and these two siblings fight often, but they are much gentler." As he was talking, they stood up across the wire, opened their mouths wide and drooled, which scared us. The keeper smiled and said not to be afraid, they are very docile to humans. "When they were abandoned by their mother, they were still breastfeeding. When we were young, we often carried them to the office to play. They were very cute." The keeper said they are the veteran animals here, and they are now ten years old. "Everyone named them Big Bear and Little Bear. The bears in the cartoons are two brothers, and here they are two siblings."

Black bear standing up

As of August 2022, the Wildlife Rescue Station has rescued 451 wild animals of 74 species (headline items), and released or transferred 248 rescued animals (headline items) to scientific research institutions, playing an important role in the protection of rare animals in the region.