After the Jinsha River passes through the majestic Qinghai-Tibet Plateau, its own turbulent river contains majestic energy before it joins the Yangtze River. So we built a majestic hydropower station between the mountains and valleys, the Baihetan Hydropower Station.
It is the world's largest and most difficult hydropower project under construction. With a total investment of 220 billion yuan, an average annual power generation of 62.4 billion kilowatt hours, 19.68 million tons of coal can be saved, and 5,160 tons of carbon dioxide emissions can be reduced.
However, such a great project, which represents the highest level of hydropower construction in China and has great development significance, has collapsed in many places after the water level dropped this month. Although the incident will not have much impact on the operation of the Baihetan Hydropower Station itself, does it prove from the side that there are some worrisome problems in the quality of the project? Who should blame themselves?
Baihetan Project
Electricity is a vital energy source for human social life, and hydropower is recognized as the best quality, flexible and clean energy source due to its pollution-free, high utilization rate and high development efficiency. In the context of the increasing tension of traditional energy sources in the world, hydropower resources have become the target of vigorous development by various countries.
The first hydropower station in China was the Shilongba Hydropower Station in Yunnan, which was established in 1912. However, the development of hydropower projects in China was slow, and until 1949, the installed capacity of hydropower in the country was only 360,000 kilowatts, which can be said to be very lagging behind, and the country has vigorously developed hydropower resources since then.
In 1954, due to the extension of the plum rainy period in the middle and lower reaches of the Yangtze River, there was a catastrophic flood rarely seen in a century, resulting in heavy losses due to flooding. At this time, the government made up its mind to study the plan for the construction of water conservancy projects on the Jinsha River upstream.
As an important river in the upper reaches of the Yangtze River, the Jinsha River has a total length of 3,479 kilometers, a stable runoff, a drop of up to 5,100 meters, and is expected to develop hydropower resources of 88.91 million kilowatts.
Since the 90s, the East China Institute has been responsible for the research of the Baihetan Cascade Power Station, for which they have studied and surveyed a large number of hydrogeology. In June 1990, the Yangtze River Water Conservancy Commission approved the State Council and officially began to implement the "Brief Report on the Comprehensive Utilization Plan of the Yangtze River Basin".
In 2010, the Baihetan Hydropower Station began to be built, and after seven years of research and demonstration, it was finally fully built in July 2017 and officially started in August. Located in Ningnan County, Sichuan Province and Qiaojia County, Yunnan Province, with a total investment of 220 billion yuan, it has created six world firsts, two world second, and two world thirds so far.
With a total installed capacity of 16 million kilowatts, Baihetan Hydropower Station ranks second in the world, and the first is the Three Gorges Water Conservancy. The single unit capacity is 1 million kilowatts, ranking first in the world. The total length of the underground cavern is 217 kilometers, which exceeds the distance from Beijing to Tianjin, ranking first in the world in terms of scale. At 289 meters high, which is about 100 stories high, the barrage arch is the third largest in the world. The maximum flood discharge capacity is 42,348 cubic meters per second, which can fill the West Lake in just six minutes, and the flood discharge power is the third in the world.
The construction technology and quality of the Baihetan Hydropower Station are also first-class according to the data and description.
In order to prevent temperature cracks, the whole dam of Baihetan Hydropower Station uses a new type of special cement independently developed by the mainland - low-heat Portland cement concrete. This kind of concrete only takes about 7 minutes from mixing to pouring, and the final concrete temperature does not exceed 8 degrees.
A total of 16 hydro-generator sets with a single capacity of 1 million kilowatts are designed and installed inside the hydropower station, and the turbines use long and short blade runners to ensure efficient and stable operation of wide loads, which is currently the largest hydropower unit in the world.
Previously, the largest single unit capacity in the mainland was only 850,000 kilowatts, and the increase from 85 kilowatts to 1 million kilowatts represents the overall improvement of the technical level of the entire hydropower equipment manufacturing industry in the mainland.
However, it is such a shining engineering business card, but there were some surprising small situations a few days ago.
Who is responsible for slope protection collapse?
A few days ago, the water level in the Baihetan reservoir area has dropped, and the slope protection that is usually hidden in the water area has also been revealed. After on-the-spot observation, we unexpectedly found that there were five or six small-scale collapses in the slope protection of the Baihetan Reservoir, and the sand at the collapse was also washed down by the water flow and accumulated in the stones below.
Reservoirs and hydropower stations are closely related, and there are generally a large number of people living around the reservoirs, once there is a problem, it will cause unimaginable disasters and pose a huge threat to people's lives and property. Therefore, the mainland has extremely strict standards for reservoir construction, especially the requirements for the safety and stability of slope protection.
As the protective structure of the reservoir, the slope protection of the reservoir can also improve the stability of the surrounding roadbed and play a supporting role. The so-called slope protection is to establish a slope of a certain slope on both sides of the reservoir subgrade, so that the subgrade presents a trapezoidal cross-sectional structure. Because of its pivotal protective position, slope protection can also reflect the overall project's ability to resist pressure and disasters to a certain extent.
There are many factors that affect the stability of slope protection, the first is the internal factor. Most of the slope protection is established according to the terrain and needs to be deeply integrated with the local environment, but if the soil rock structure of the local environment has various problems such as fracture and arrangement, it will cause problems with the stability of slope protection.
The second is the issue of water storage. The reservoir has a storage capacity of tens of billions of cubic meters, which is constantly impacting the slope protection, and in the long run, it may cause the external rock layer to collapse. Sometimes there is a chemical reaction between the water material and the rock formation, which can also lead to a decrease in the strength of the slope protection.
The third is the layout and daily activities. At the beginning of the construction of slope protection, it is necessary to fully consider the overall layout and the subsequent stability decline factors, adopt different construction methods according to local conditions, strengthen the compressive structure of reservoir slope protection, and comprehensively consider the construction.
Secondly, human activities will also have a certain impact on the reservoir, and a small number of residents are not aware of it, and they are unaware of it when they carry out some private activities that are harmful to the stability of slope protection. Coupled with the impact of climate temperature differences, the problem caused by the decline in slope protection stability is caused by several factors.
If we take a closer look at the collapse of the slope protection in the Baihetan reservoir area, we will find some clues. On the smooth and intact slope protection surface, we will find that the connecting gaps between each hexagonal brick are tightly filled with cement. On the other hand, the gaps between the bricks in the collapse area are not filled with cement, and the gaps between the bricks are wider in some larger collapses. After being washed by the current, the sand under the bricks was also swept to the shore.
We can speculate that this phenomenon is attributed to the laziness of the workers during construction, or it can be explained by the impact of the water flow over the years. However, no matter how it can be justified, it is an indisputable fact that there are defects in the quality of slope protection in the reservoir area, and we can even speculate whether there are potential safety hazards in other engineering projects because of the small view.
So what are the rescue and remedy measures for this slope protection collapse?
First of all, a series of temporary emergency rescue can be carried out, such as sandbag glanding, which can be used to cover the collapse area in some areas where the local loosening is loose and the wind and waves are small.
Another example is the rubble protection, in view of the large wind and waves and the collapse situation, small pebbles or gravel are used as cushions to temporarily resist the continuous impact of wind and waves, which is more suitable for the slope protection of Baihetan.
Finally, there is the lead wire gabion protection, which is aimed at the situation of extreme wind and waves and serious damage and losses. Use the prepared gabion to move it to the damaged area, and then tie it with lead wire and fill it with stones to increase the resistance to compression.
These are temporary rescue measures, to really solve the problem of slope protection damage, or to carry out local overlay, permanent reinforcement and other methods. However, before solving the problem of slope protection at Baihetan, should we reflect on the root cause of the problem?