The work and the tecnique: Xiaolangdi Dam, China

The Xiaolangdi multipurpose dam was designed to be one of the largest clay-core rock dams ever built in the world. 

Beyond its basic purpose of producing energy, the facility was designed to fulfil various needs, such as flood control for the lower section of the river, improvement of sediment management to help delay changes to the riverbed, controlling the flow of ice to prevent flooding during the winter period, and providing water for civil, industrial and agricultural use.
The earth and rock embankment that makes up the main body of the dam is specifically intended to stabilise the amount of water flowing into the lower section of the river, controlling the sedimentation of materials and preventing sheets of ice from getting through in the winter. A cross-section view of the embankment reveals that it consists of 17 zones of filler materials, each with specific characteristics to meet the various different functions of the design. The excavation volume was 8.5 million cubic metres, nearly 8 million of which was rock.

Following completion of the diversion works, as well as the construction of one dam upstream - which forms the tip of the main dam - and another downstream, work could finally begin on the main dam. Throughout the entire construction period, measures were put in place to drain and treat the water. The consolidation and waterproofing works involved building a jet grouting interception wall below the cofferdam located upstream spanning a total surface area of 9,910m² with an average depth of about 30 metres, as well as a concrete cut-off wall built beneath the main core of the dam, which was achieved using the bentonite slurry trench construction technique. Work was successfully completed on the dam at the end of November 2000, a whole 13 months ahead of the contractually agreed completion date, and the fully operational facility can now generate up to 5.1 TWh a year thanks to its six turbines.