In the mold of productivity
Precast pieces help put construction of the Santo Antônio hydroelectric plant ahead of schedule.
Like pieces of a Lego set with various geometric shapes and sizes and volumes. This is a simple definition for the precast pieces used in civil construction. But on this particular project, precast pieces mean flexibility, quality and safety.
These pieces were first used in some countries during post-World War II reconstruction. They became popular in Brazil in the 1950s, when businesses began to streamline and industrialize processes. More than 60 years later, the presence of precast pieces in large projects is growing steadily, and their applications are becoming more and more challenging.
Odebrecht Energia is building one of the largest hydroelectric projects in the country in the Brazilian state of Rondônia: the Santo Antônio plant, which will have 44 turbines and generate 3,150 MW of energy. According to the construction master plan, developing new precast pieces is key for optimizing the work, the safety of the company’s members and the preservation of the environment. “In construction, the industrialization of some processes boosts the quantity and quality of activities while ensuring people’s safety and quick results,” explains Project Director Mário Lúcio Pinheiro.
The precast pieces are manufactured by 240 professionals in two yards near the site where they will be used. “We produce 400 units per month, weighing from 5 to 28 tonnes apiece, and we plan to increase production by 100 units over the next six months,” says Yards Manager André Lima.
The project involves 827 different types of precast pieces and more than 11,400 have already been installed. “Precast pieces involve more assembly and less casting. The more we reduce the casts used for these structures, the faster the work goes,” says Technical and Engineering Manager Fernando Dias Resende. He adds that the pieces are used as needed, based on feasibility. “Precast pieces for the gallery [providing access for technicians and equipment used for turbine maintenance], the parapet walls and jersey barriers are widely used in large projects. Our challenge is to create original items, and we have already developed a few,” he explains.
Combining new solutions
One of the new pieces specially designed for the plant is a precast suction tube (a cone-shaped hydraulic device located at the turbine exit). The idea came up after using the conventional method – wood concrete forms – for Generator Group (GG) 1, on the right bank of the Madeira River. “Wood forms need repairs and, moreover, their reuse rate is poor,” says Fernando Resende.
The Engineering and Production teams got together with the designers to make the idea a reality, and after six months of discussions and drafts, the precast piece was created with a metal form. The teams designed shapes weighing 11 to 21 tonnes according to the crane’s available lifting capacity.
The new pieces are already being installed in the suction pipes for Generator Group 2 and will also be applied to Generator Groups 3 and 4, all on the left bank. Each pipe consists of 20 pieces, and a total of 36 turbines will be installed using 720 precast pieces of different shapes and weights. To facilitate transport, the largest precast pieces in the design are made right next to the site where they will be used.
“We have reduced the execution time for the layer from 60 to 45 days and increased productivity, safety and environmental conservation,” says Rodrigo Galli, Production Manager for Power House 2. He explains that, as a result, members are less exposed to the risk of accidents, and 948 m3 of timber and 2,800 m3 of falsework (steel structures for bracing and securing reinforced concrete) per unit are no longer required.
When precast pieces cannot be used, the process is industrialized by assembling rebars in advance. “Instead of taking hundreds of rebars to be assembled at heights of dozens of meters, we assemble the structure on the ground and a crane positions it for concreting,” says Rodrigo Galli.
These methods also keep the work fronts clean and organized and contribute to the quality of the structure’s finishing. “The pieces don’t need touch-ups, because they are ready for use, minimizing rework. Each structure is fully finished,” says Quality Control Manager Almir Chieregato.
“The pieces do not need touch-ups, because they are ready for use, minimizing rework”
Key part of river diversion
Another precast piece developed for this project was the trunnion beam used to support the main spillway, which is essential to the civil and electromechanical interface of the project. The trunnion beam supports the arm of the sluice gate, which controls the level of the plant’s reservoir. Using the conventional method, the beam would be made by installing lateral bracing supported by a concrete pillar. Rodrigo Galli explains that the precast piece has reduced the amount of work done at height – the beams are 30 meters off the ground – because they used cranes to install the parts. He observes that this solution has slashed costs by 50% and reduced the work schedule by 20%, from 35 to 25 days. “We have ensured that we will finish the civil engineering works on schedule so we can begin the electromechanical activities and start diverting the river.”
The diversion of the Madeira River officially began on July 5, in the presence of Brazilian President Dilma Rousseff, Mines and Energy Minister Edison Lobão, and local and federal authorities, along with Marcelo Odebrecht, President and CEO of Odebrecht S.A., Henrique Valladares, Entrepreneurial Leader (CEO) of Odebrecht Energia, Eduardo de Melo Pinto, President of Santo Antônio Energia, and other leaders.
President Rousseff triggered the device that opened the spillway floodgates, allowing water to flow through the structure. “Santo Antônio represents a commitment to the Brazilian environment and sustainable development,” she said.
Mário Lúcio Pinheiro observes that this event marked the beginning of a new phase of the project. “The ideas conceived and lessons learned on the right bank will be applied on the left. We will work hard to ensure that the first turbine starts generating power by December 2011, and the other 43 are operating by the end of 2015,” he adds.
According to Rodrigo Galli, teams from the company’s other projects have visited the jobsite to familiarize themselves with these new ideas so they can apply them in the future.