Blast-placed membraneless rockfill dams for hydropower schemes

Abstract

One of the most widespread typesofdam adopted in the construction of hydropower schemes in mountain regions is the rockfill dam built from local natural materials. For dam heights of the order of 250-350 m, the fill volumes become very large (50-120 million m s) and the construction of such hydropower schemes requires very high capital and labo~ inputs. For these dams the problems of reducing the cost and time of construction have not been wholly solved. Therefore, the development and application of fundamentally new and progressive design and construction technologies for high earth and earth-and-rockfill dams must become the principal trend in dam construction in mountain regions. In the construction of dams from local materials the following two stages stand out [1]:Stage I. Foundation preparation, which is accompanied by the driving of diversion tunnels and construction of cofferdams, dewatering of the river bed, cleaning the excavation on the area of contact between the foundsdon and the water-retaining elements of the dam (core or membrane), and blanket and curtain grouting.Stage 1I. Construction of the dam prism, including work on the winning of materials from quarries, the mechanical processing of material suitable for placement in the water-retaiuing elements of the dmaa; transport of the excavated and processed materials from quarries and plant to the dam; and the dumping, spreading, and compaction of the various materials in the dam prism.The execution of the above-mentioned interrelated works, where the dam dimensions are increased and the construction operations are shifted deep into mountainous regions, is rendered substantially more complex owing to the difficult access conditions in narrow gorges. The steepness of the slopes complicates the development of quarries for the dam rockfill, and the substantial distance of the loam, gravel and sand borrow pits from thedamsite gorge, located in the main rock massif, give rise to high haulage costs. The difficulties are aggravated immeasurably by the low capacity of modern transport equipment in comparison withthe growing volumes of dams. Furthermore, the construction of a high rockfill dam of traditional type necessitates the driving of a large number of special transportation and auxiliary tunnels and various types of shafts, whose total length together with the hydraulic tunnels can amount to 35-40 km (e.g., at the Nurek and Rogun hydropower schemes). The combination of these factors causes a marked increase in the length and complexity of the communication services, the fleetsofmechanical and service plants, the number of personnel, the volume of design work for items in the work areas and the township.The unfavorable effect of the above-mentioned factors is markedly reduced where dams are constructed by directional blasts. This method, which is the most expedient under poorly accessible, mountainous conditions, enables large economies to be effected by a single heave of the whole voktme of construction material into the dam prism by means of explosiv...