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Sanbanxi HPP, located in Jinping County of Guizhou Province, has a concrete-faced rockfill dam (maximum height 185.5m) and an installed capacity of 1000MW. Its dam building technology was a key national scientific research project in the Tenth Five-Year Plan period. The application of such technologies as damming with super-hard rock and realizing flood retention in one dry season offered new ideas for the design and construction of 200m-level high CFRDs.
The project is mainly for power generation and boosting the benefits of downstream cascade hydropower stations and concurrently for flood control, cultivation and tourism. Its reservoir has a NPL of 475m, corresponding to 3.75 billion m3 of storage, and an effective storage of 2.62 billion m3. The project can play significant regulation and compensating role for the lower 13 cascade developments. In the future it can increase the firm output and annual energy of the lower cascade stations by 203MW and 1,470 GWh, respectively, and currently it can raise the firm output and annual energy of the Hongjiang, Wuqiangxi and Lingjintan hydropower stations by 55MW and 640 GWh, respectively. The main construction was commenced on July 1, 2002, and the total construction period is four years and nine months.
Main Technical Features and Key Technical Issues:
The dam body filling materials were tuffaceous sandy slate from quarry and palimpsest tuff, palimpsest tuffaceous sandstone, and palimpsest tuffaceous slate from excavation of structures at the dam site. The materials for dam building feature in complex rock type and great difference in strength. The saturated uniaxial compressive strength of rockfill materials varied from 15MPa to 235MPa and could be up to 300MPa, and there were hard rock, extra-hard rock, and strongly weathered rock with low strength.
Realizing flood retention in one dry season was adopted as the mode of passing the flood season in dam construction. The mean monthly filling intensity reached 400,000 m3, and the peak was 600,000 m3. The temporary section height, total filling volume and filling strength of the dam body ranked first in China.
The dam site is at an asymmetric V-shaped valley with high and precipitous slopes on both banks and a width-height ratio of 2.28, so the dam is subject to 3D arching effect. A 50m-high toe wall (retaining wall) was built at the interface to the spillway on the left bank.
Because of alkali reactivity of the concrete aggregate, appropriate amount of fly ash was added to control the total alkali content in concrete and to effectively inhibit the alkali reactivity of the concrete.
The construction period was shortened to only four years and nine months through design optimization.
Reasonable blasting and rolling compaction methods and technologies were employed. For instance, rock gradation of blasting was improved through approaches of coupling charge, proper increase of unit powder consumption and selec_tion of rational drilling and blasting parameters, a certain proportion of weathered rock was mixed, and 15-18t towed heavy-duty vibratory rollers were utilized to make the compacted dam body have relatively high dry density and relatively low porosity.
As for the design of CFRD, such measures were employed to ensure the safe operation of the dam as specially designed cushion cells, new type of cohesionless fine silt for waterstop structure, and clay blanket on the upstream face.
Concrete face slab on the dam surface – connecting plate was furnished at the auxiliary dam of the CFRD in accordance with the topographic and geological conditions at the dam site so as to save the work amount, elongate seepage path and decrease seepage.