Construction workers cast the last concrete unit for the main section of the mammoth Three Gorges Dam on Friday morning in the middle reach o f the Yangtze River. The final concrete placement is due to finish on Saturday, which will mark the completion of the dam's main wall. [Xinhua]

The equipment will measure the impact of the explosion to prevent the blast from damaging the main dam 114 meters downstream on June 6.

The cofferdam, which has been in use since 2003, is 580 meters long and 140 meters high. About 192 tons of dynamite have been placed below the waterline to demolish the dam above the 110-meter mark, a total of 186,000 cubic meters of concrete.

Scientists will measure the surge, ground swell, vibrations, sound waves, noise and other data, said Zhao Gen, a senior engineer.