Rational methods of design and construction of antifiltration elements of blast-fill dams

Abstract

Further development of the fuel-energy complex of Russia leads to the need for accelerated development of hydropower in its eastern regions, where it is rational to use, as main water-retaining structure of a hydraulic project, an earth or rockfill ~m. In narrow mountain canyons such dams can be constructed by the method of directed blasting~ of the fill or loosening of rock material.The use of directed blasts for earth dam construction makes it possible to substantially reduce the volume of costly preparatory work, quarrying installations, road systems, and electric equipment for the construction site, as well as the need for earth excavation equipment and means of transportation. In some cases it is possible to omit the construction of temporary cofferdam.q and tunnels for diversion of flows during construction.Tile above circumstance leads to a significant reduction of the labor and, consequently, of the construction time. Moreover, construction of earth dams by directed blasting in regions of Siberia, the Far East, the Caucasus, and the North of our republic reduces the damage to the environment on account of decrease in the area of construction material pits.The main shortcoming of blast-fill dams is their high permeability, which results in large seepage losses through the dam body and decrease in the electric energy output at hydraulic developments intended for energy production.In cases in which in accordance with the operation conditions of the hydraulic development it is necessary to ensure minimum water seepage losses, it is essential that the rock mass pile which forms the ~m body be provided with external or internal antif'fltration elements.The teclmical-economic effectiveness of the use of blast-fill dams in the given ease must be preserved if the techniques for construction of the antifiltration elements does not annul the basic advantages of this method of construction of earth structures.In foreign practice, for example as described in [1], the blast-fill mass is used as downstream shell, and subsequently the dam is built up by the traditional method of layer-by layer placement and rolling of the fills (Fig. 1). In this ease, for construction of the antiffltration element, filling up of the mass to the design section, and placement of fills in the transition layers and the f'dter, it is necessary to construct a diversion tunnel, to exploit construction material pits, and to construct roads from the construction site to the pits. In many cases this circumstance may reduce to zero all the advantages of the construction of earth dams by directed blasting.At the "VODGEO" Institute, for many years investigations have been carried out to develop methods of construction of antiflltration elements by means of silting-up, inwash of soils into the body of the blast-fill dam, or hydraulic fill placement of low-permeability soils in the hollows formed by the rock shells constructed by blasting (Fig. 2). In this case there is the possibility of combination of two highly effective methods of construction of w...