Multilevel schemes for the layout of temporary and permanent spillways are presently used in the construction of high-head hydrodevelopments.Such schemes, corresponding to the technical level attained by Soviet gate construction, provides the release of considerable flows over a wide range of heads up to 100-130 m. The number of levels of spillway structures at high-head hydrodevelopments can be reduced by using high-head gates.This can effect a considerable economy, especially in the case of spillway tunnels, since the cost of each level amounts to 10-20 million rubles.At present designs have been developed for deep, mainly vertical-lift and radial gates which can operate satisfactorily under heads to 200 m for opening areas of up to 30 m 2. However, if the temporary discharges during construction are great, the spillway is built with a large number of openings, which adversely affects the hydraulics and leads to an increase in the spillway face, rock excavation, and capital expenditures. Therefore, the need for creating high-head gates covering openings greater than 30 m 2 at heads to 200-300 m is quite pressing.
When designing hlgh-head spillways the provision of protection of the waterway of the structure from the destructive action of the high-velocity flow is a complex problem. It is often economically expedient to use low-head spillways as the service ones in the case of high heads and also to closely arrange or combine the power and spillway conduits. In these cases it is necessary to create conditions for dissipating the excess kinetic energy of the discharge behind the service gates to prevent cavitation erosion of the linings and scour in the lower pool, to reduce the dynamic loads on the structural elements, and to provide normal conditions of operation of the power conduits.For a number of years scientific laboratories of our country have been investigating socalled eddy spillways [i] based on the effect of swirling the flow in the exit section behind the dlscharge-regulating gate. It was established as a result of these works that when the flow is swirled the pressure increases and the wall velocities decrease as a consequence of the effect of the!~centrifugal forces on the walls of a cylindrical tunnel. This increases the cavitation safety of the spillway. The use of the interaction of swirled flows makes it possible to reliably dissipate their excess kinetic energy [2, 3].Thus the investigations showed the prospects of spillways of this type for high-head hydraulic structures [4]. An analysis of the expected technical--economical, layout, and operating characteristics shows their competitiveness and, in a number of cases, advantages over spillways of the traditional types, particularly over multilevel spillway systems [5, 6]. At present research is practically completed, considerable empirical data have been accumulated, methods of calculation hay been developed for the majority of spillways of this type, and a pilot model wlth an 800-unmdiameter exit conduit has been tested [7]. The necessary data are available for converting from research to practical introduction. However, the obstacle on this path was the complexity and labor intensity of construction and the technological inefficiency of the majority of the designs proposed by researchers.With consideration of this, at the hydrodynamics laboratory of the Moscow Special Design Department of Steel Hydraulic Structures (Mosgidrostal') investigations were aimed at developing primarily rather simple designs of bottom eddy spillways based on using the usual types of high-head sates mastered by Soviet industry: vertical-llft and radial. The possibility of realizing such a spillway system was examined in one of the publications [8]. As a result of the given work, a spillway system in which dissipation of the kinetic energy is accomplished by the interaction of concentric oppositely swirled flows was proposed and investigated on a model (Fig. 1).The spillway operates in the following way. Two flows from the entrance sections 1 enter the gate chambers with the emergency-guard 2 and service 4 gates, from under which in a free-into-air regime behind the gates (via...
On the basis of analyzing the experimental data in [I] a relation between the radius of the loosening crater (r) and the parameters of the drilling and blasting operations in the case of row blasting of shothole charges is proposedwhere QI is the mass of the charge in one shothole; L is the depth of the shothoies; ab is the pattern of the charges; s is the length of stemming.The time of projection of rock pieces is 0.I sec in the case of instantaneous blasting and 0.i + (n -l)tsh in the case of short-delay blasting (n is the number of short-delay periods, tsh is the delay interval between series).For charges of each of the short-delay periods the covering is measured from the extreme shothole of the short-delay period.Scatterless blasting will be provided when conditions (3) are fulfilled regardless of the massiveness of the shelters.
At the present time there are experimentally justified and reliable methods wMch permit indicating, with assurance, under which hydraulic regimens cavitation may develop in any element of a spillway structure, or on any rough surface of such a structure. However, the available data indicate also that, frequently, for structures operating under heads of 40-50 m or greater, the complete elimination of cavitation is practically impossible or requires the application of complex engineering measures. For this reason it would be desirable to allow a certain degree of cavitation, provided the resulting destruction is not excessive and is acceptable from the standpoint of reliable operation of the structure over a sufficiently long period. The possibility of such a solution is confirmed by the operating experience with many structures which have operated reliably despite cavitation phenomena. However, the cases in which inadmissible and catastrophic destruction of isolated elements of hydraulic structures has taken place under cavitation [1] were in the past always used as specific warnings against such an approach.The present state of research on the problem of the mechanism of cavitation erosion of materials and on the processes which determine its development is not sufficient for making quantitative predictions of the extent of cavitation destruction, especially for the cavitation stages corresponding to a very intense erosion.The tests performed indicate that it is possible to establish the form and stages of the cavitation phenomenon for which the erosive action is either very small or practically does not take place over a sufficiently long period of operation of the structure. For hydraulic structures the most characteristic feature is the development of the so-called "separation" forms of cavitation, which take place when the water flows around different projections,
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