Experimental work concerning the grouting of joints in the Krasnoyarsk hydroelectric plant dam

1. The type of formwork, the dimensions of the blocks and concrete lifts, the composition of the concrete mix, the concrete-placing techniques, and the temperature regimen of the concrete should be selected in such a way as to obtain the maximum possible and most uniform separation of the joints with the minimum possible roughness of the surfaces. This is achieved through the use of smooth formwork and the levelling of the first-stage concrete surfaces. The experimental work conducted at the Krasnoyarsk hydroelectric plant permits working out some recommendations for the most rational application of grouting techniques under similar conditions. 2. For primary grouting, use should be made of linear outlets, which ensure the best hydraulic communication between the grouting system and the air passage. In particular, use can be made of a system with a horizontal outlet in the lower portion of the layout and with an air-removal slot in the upper portion. The distance between them predetermines the expected degree of hydraulic permeability of the joint. 3. Perforated and spring outlets may be used for secondary and multiple grouting, provided their construction is improved by increasing the watertightness of the valve. To reduce the limiting effect of the concrete upon the deformation of the sleeve in perforated outlets, the cast rubber in the sleeve should be replaced by porous rubber having a larger thikness. 4. The multiple grouting system should be comprised of several loops. In the case of small absorption of the grout during grouting, it is necessary to organize continuous or impulse circulation of the flow in the pipe system and in the air-removing slots. Immediately after the primary grouting the conduits should be washed. In the case of a system which is not watertight, washing should continue until the grout sets in the joint, that is, for not less than an hour. 5. The criterion for thickening the injected grout could be the stabilization or the slow variation of the parameters of the grouting process-absorption from the tank, overflow from the air conduit, etc. 6. Taking into consideration the tendency toward increase of the area of grouting layouts in the dams now being constructed or designed, it is necessary to replace the 11Gr pumps now used by larger ones; this would permit increasing the pumping pressure, the additional separation of the joints, and the velocity of the injected grout and would ensure the required quality of the grouting operations.