Spanning more than 2,3km across the Yangtze River; 2 309m wide; and towering 181 m in height, the Three Gorges Dam retains almost 40-billion m3 of water in its 1-million km2 catchment area.
The plant was built by the Chinese Central Government to finally tame the “Long River”, described by American writer and novelist, Pearl Buck, as the “wildest, wickedest river on earth”. This is due to the extensive destruction and loss of life that it wreaked on river basin communities when it burst its banks.
A further motivation for building the infrastructure was to generate large amounts of clean and cost-effective electricity and achieving water security for China’s growth.
When the Three Gorges Dam started operating in 2012, it was officially the world’s largest hydroelectric plant, generating 22 500MW of electricity.
However, this is not the only record that this mega-infrastructure project, which the Chinese Central Government says cost US$37,23-billion, has broken.
The Three Gorges Dam can also stake its claim to being the largest concrete dam in the world. A total of 14,86-million m3 of concrete was placed to construct the dam cross-section, alone.
This is in addition to the enormous quantities of concrete used to construct the other components of the hydropower station. Over the 18-year-long construction period, China Three Gorges Corporation (CTGC) placed just under 30-million m3 of concrete, reinforced with 354 000 t of steel.
In 2000, the Central Chinese Government also broke records for the largest yearly, monthly and daily concrete pours ever undertaken – a staggering 5,48-million m3, 553 500 m3 and 22 000m3, respectively. This was also a proud moment for the 25 000 individuals who worked on the project when it peaked.
Due to the complexity associated with handling and placing such large quantities of concrete, various processes were first simulated and the preferred method then refined and put into practice.
Seven computer-controlled concrete batching and mixing plants were deployed. The two located downstream on the right bank each had a capacity of about 350m3/h. This was bolstered by the between 240m3/hour and 400m3/hour production capacities of the two and three batch plants located upstream and downstream of the left bank, respectively. Concrete for the construction of the navigation locks were supplied by two adjacent concrete plants located on the downstream right-side of the locks.
All of the specified aggregate and sand excavated from the foundation pits were used for concrete production and supplemented with sand manufactured by a vertical-shaft impactor.
Most of the concrete was placed using six tower belts, each providing a peak productivity rate of between 100 m3/h and 200 m3/h. Additional capacity came from haul trucks that transported concrete to feeder conveyors or crane lay-down buckets wherever necessary.
As the dam gradually reached its final height, the conveyor belts were lifted with six tower cranes equipped with jacks. Concrete was also placed with the crane’s swinging telescopic conveyors that had a 450m3/h design capacity. A mobile crane delivered concrete from a large haul truck to construct the dam’s left wall.
Maintaining optimal curing conditions was critical. This is considering the substantial heat that concrete placed in large quantities generates when it sets, compromising its strength.
The system implemented to maintain concrete at about 7oC was the largest and most sophisticated at the time.
Firstly, the aggregate regulation bin in the secondary screening circuit was used to air-cool the coarse aggregate. Secondary aggregate cooling then took place in the mixing plant’s material bin. This clever process included ground-air cooling and a highly efficient fan and distribution system that created a cool-air circulation system inside the bin.
The batching plants also featured cold-air, water and sheet ice-cooling capabilities. Moreover, post-placement cooling pipes through which chilled water was pumped were used in areas where concrete was placed en masse. These interventions also helped to maintain concrete temperatures during the warm summer periods.
A high-performance 60MPa concrete mix was designed to construct the about 231 000m2 of water-tight concrete walls.
An artificial aggregate consisting of non-alkali active granite was selected as the most suitable material to meet the concrete’s high-performance requirements. Alkali content was strictly controlled to less than 0,5% in the cement clinker and below 2,5kg/m3 in the cement and Class I fly ash. Containing a high proportion of fine particles, the fly ash improved the workability of the concrete and slowed the alkali-active reaction to provide savings in slurry consumption. In turn, this helped to prevent temperature-related cracking and dry shrinkage. A high-quality and -efficiency water-reducing agent was also incorporated into the mix to further reduce water consumption savings already achieve by fly ash from 110kg/m3 to 85kg/m3. Increasing the amount of fly ash by reducing the water-to-gel-ratio also improved the durability traits of the concrete.
To better manage the swift placement of large volumes of concrete, a comprehensive set of quality assurance and construction systems were developed specifically for this project.
Real-time monitoring; dynamic adjustment; and optimal regulation of the entire construction process was supported by an integrated computer-monitoring and -control system.
However, many have questioned whether the extensive time, money and effort allocated to this project were worth it. These doubts again came to the fore in 2020 when the dam failed to tame the river during the heaviest average rainfall in nearly 60 years. 158 people died or went missing; more than 3-million residents were displaced; and over 54-million citizens were affected by the catastrophe in some way.
Certainly, the dam has also had significant dire environmental and social consequences that cannot be ignored.
Moreover, in 2002, cracks were identified in the dam wall. The fissures were promptly repaired but have since reopened.
However, Chinese authorities continue to stand by their project. They note that it played a crucial role in mitigating a severe disaster during the recent floods. Then there are the other host of benefits that it has provided over the years. This includes power generation; navigation; aquaculture; tourism; ecological protection; transfer of water to where it is needed the most; irrigation; and water security.
