The placing of a low-slump concrete, four layers in 2.3m lift
Tractor mounted vibrators at Emosson Dam, Switzerland
- Temperature rise, which will depend upon the heat of hydration of the cement, the quantity of cement per cubic metre, the concrete placing temperature and the rate of construction;
- Heat dissipation, which will depend upon the conditions of exposure - including the temperature of the underlying concrete and the thermal diffusivity of the concrete. If it is considered necessary to heat the underlying concrete the rate of rise of its temperature should not exceed 2° Celsius per day;
- The effects of restraint from a cold surface, i.e. rock or concrete say 14 days old, it will depend upon the temperature gradient which can be reduced by placing concrete in half lifts for a predetermined height, say 3m above the cold surface;
- The arrangement of cooling pipes - at 0.25 and 0.75 of the height of the lift may be more efficient than on the top of the old lift and at mid-height of the new lift. The horizontal spacing will depend upon the rate of heat removal required and the temperature of the cooling water (i.e. river water of varying temperature or refrigerated water);
- The local weather conditions - humidity, temperature and wind.
- Is it permissible to design for tensile stress in the concrete?
- Will arching of the dam result in overall economy?
- Are longitudinal contraction joints necessary in large gravity dams?
- Can the transverse contraction joints be omiited, located at wider spacing etc?
- What clean up is necessary on horizontal construction joints?
- Should the height of lift be specified by the designer?
- Should the cement content of the concrete be specified or only the properties required in the concrete?
- Can the dams of intricate shape be justified?
- Should ancillary works be separated from the dam to minimise interference with a continuous or cyclic process of dam building?
- What is the optimum layout and design for galleries?
The Waterways and Concrete Dams Group specializes in structural, hydraulic, and quantitative risk analyses, evaluations, and designs of appurtenant hydraulic structures (such as spillways and outlet works) for both concrete and embankment dams. The Group is effective in undertaking and completing work ranging from long-term, complex technical activities to small, "quick-turn-around" technical studies. A large portion of the Group's work and experience involves safety of dams evaluations.
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