JACI PARANÁ, Brazil — The revolt here on the banks of the Madeira River, the Amazon’s largest tributary, flared after sunset. At the simmering end of a 26-day strike by 17,000 workers last month, a faction of laborers who were furious over wages and living conditions began setting fire to the construction site at the Jirau Dam.
Throughout the night, they burned more than 30 structures to the ground and looted company stores, capturing the mayhem on their own cellphone cameras, before firefighters extinguished the blazes. The authorities in Brasília flew in hundreds of troops from an elite force to quell the unrest.
Men in camouflage fatigues still patrol the sprawling work site, reflecting a dilemma for Brazil’s leaders. Even as they move to tap one of the world’s last great reserves of hydroelectric power, the Amazon basin, strikes and worker uprisings at the biggest projects are producing delays and cost overruns.
“No one burns anything if they’re satisfied,” said Altair Donizete de Oliveira, a union leader here in Brazil’s western frontier. He listed salaries, cramped living quarters and requests for more home visits among the grievances that were contributing to the festering tension among the laborers, who number in the tens of thousands at various work sites in the Amazon.
Brazil is leading a rush among South American nations to build an array of dozens of dams in the Amazon. The authorities expect at least 20 important hydroelectric projects, including the Jirau and Santo Antônio Dams here in Rondônia State, to be built in Brazil over the next decade. Elsewhere in the Amazon, work has begun on Brazil’s biggest dam project, Belo Monte, an effort to divert the Xingu River requiring more than $12 billion.
The advance of the projects has opened Brazil to criticism from environmental groups, which say that the displacement of indigenous peoples and the flooding of swathes of rain forest — potentially releasing large amounts of methane gas — outweigh the dams’ benefits.
But officials argue that Brazil needs the dams to meet the demand for electricity, which is predicted to surge 56 percent by 2021. President Dilma Rousseff forcefully defended the projects in April, accusing opponents of living in a “fantasy” realm if they thought Brazil could improve living standards with renewable energy alone.
“I have to explain to people how they’re going to eat, how they’re going to have access to water, how they’re going to have access to energy,” Ms. Rousseff said.
Brazil’s huge wager on the dams is illustrated by the urgency with which officials are assessing the labor problems at Jirau, which was stricken by a previous mutiny in 2011, when workers set fire to 35 sites that served as living quarters and 45 buses. Rondônia’s governor recently pleaded with Brasília to send troops to occupy the dam projects. Gilberto Carvalho, a top aide to Ms. Rousseff, said the unrest in April was “banditry” that required a strong response.
Together, the upheavals have delayed the completion of the Jirau Dam by months. Strikes have also recently halted work at the Santo Antônio Dam, which is also on the Madeira River, and at Belo Monte, where thousands of workers have arrived in the remote city of Altamira.
Concerns about a potential domino effect of labor agitation at other big infrastructure projects are emerging as workers push for wage increases at a time when Brazil’s unemployment rate, currently 6.2 percent, is historically low.
Union officials here say that information about strategies for obtaining better wages and benefits is rapidly shared in text messages and e-mails among crews working at different ends of the Amazon, allowing unions to quickly exert pressure on employers.
Outside the Amazon, recent strikes, some of them violent, have also disrupted projects under construction by the oil giant Petrobras, including the Comperj petrochemical complex in Rio de Janeiro, the Barra do Riacho port in Espírito Santo State and the Abreu e Lima refinery in the northeast.
Although Brazil has reduced income inequality within its borders, the wages for manual laborers here still lag behind those in richer industrialized countries. Starting salaries at the Jirau Dam remain about $525 a month in a country where the cost of living rivals or surpasses that of the United States.
“My pay here is a disgrace, half what I got in Angola,” said João Batista Barbosa Arce, 29, a construction worker who came to Jirau after working for a Brazilian construction company on an African dam project. He said he lost all his belongings in the arson in April.
Executives overseeing the dam project dispute the assertions that wages here are too low by Brazilian standards, or that living conditions are dismal, saying that the workers have access to Internet cafes, gyms, pool halls and even movie theaters that show “picante,” or racy, films.
“Every effort is made to humanize the conditions for the thousands of men and women working here,” said José Lucio de Arruda, a director of the venture that will operate Jirau, controlled by the French energy giant GDF Suez in partnership with two Brazilian state-owned electricity companies and Camargo Corrêa, a construction company.
Still, nerves remain on edge at Jirau, which is scheduled to start producing electricity in 2013. The Brazilian Intelligence Agency, which is known as ABIN, has closely monitored the situation, and hundreds of military police officers from the National Public Security Force roam the grounds in Mitsubishi pickup trucks.
“It’s strange to see police on patrol now, but also reassuring,” said Gua Xiaoyi, an employee of Dongfang Electric, a Chinese company that is providing turbines for Jirau.