The intense development of natural resources of Eastern Siberia and Central Asia is making it necessary for hydraulic engineers to construct dams under complex hydrogeological conditions, on foundations Containing soluble rocks. This is related to the fact that the eastern part of the European sector of the USSR, East-ernSiberia, and Central Asia are zones of the wide distribution of haiogenic ro~ks, which are represented here mainly by gypsum, anhydrite, and halite.

The use of the energy of a blast for constructing profile earth structures began for the first time in the Soviet Union in the 1930s. Originally small embankments for industrial installations were constructed by the directional blasting method. Later this method began to be used for constructing dams and embankments. During the past 15-20 years such large structures were constructed by massive directional blasting as the 72-m-highmudflow protection dam at Medeo; the 65-m-high dam of the Baipaza hydro development on the Vakhsh River; the 91-m-high embankment across the gorge of the Akh-Su River; the 50-m-high experimental dam on the Burlykiya River.Comprehensive investigations were carried out on these structures, which expanded the amount of knowledge about the construction and seepage properties of the rock of the body of dams constructed by directional blasts~ The results of the investigations showed that earth dams constructed by this method have a high reliability. Thus the mudflow-protective dam at Medeo withstood a catastrophic mudflow in 1973.

A number of impounding structures have been constructed in our country by means of blasting.The largest of them are the mudflow-control dam at Medeo, the dam of the Baipaza hydrodevelopment on the Vakhsh River, the height of which exceed 60 m, the 90-m-high dam on the Akh-Su River in Dagestan, coefferdams of the Nurek and Chlrkey hydrodevelopments, and a number of others.Thus the Soviet Union can rightfully be considered the pioneer of this method of constructing dams. Construction experience shows that the use of blast-fill dams at hlgh-head hydrodevelopments will have a maximum economic effect, since their construction can be accomplished in a shorter time and with smaller capital investments.However, the construction of dams by the blasting method has nonetheless not gained wide use. The main reason for this is the lack of knowledge about the properties of the material in such structures.An experimental 50-m-hlgh dam was constructed by the blasting method in February 1975 on the Burlyklya River* in the Kirgiz SSR ( Fig. i) for the purpose of obtaining the necessary data for substantiating the blast-fill dam project of the Kambaratln hydrodevelopment. To conduct the investigations on the experimental site, 10 shafts were driven to depths of 21-47 m at five sites (Fig. 2). These shafts were used during sinking for determining the granulometrlc composition, unit weight, and permeability of the earth over the height of the structure and subsequently (after filling the reservoir) as plezometers for measuring the drawdown curve of seepage [i].The seepage characteristics of the soll in the dam were determined at several water levels in the reservoir.The seepage drawdown curve for the maximum water level in the reservoir is shown in Fig. i. Table 1 gives the water-level elevations in the shafts at different water levels in the reservoir.The seepage properties of the soil composing the dam proved to be different in different zones.The central zone, located between shafts 1 and 3, has the maximum water-retalnlng capacity and the zones of the upstream and downstream shoulders of the dam have the minimum.Analytic methods were used for determining the numerical values of the permeability coefficients of the soll in the different zones of the dam. The permeability coefficient was determined by the equations of steady plane seepage for discharges and water levels in the shafts and upper pool recorded for 15-20 days. The values of the permeability coefficient were determined twice at the save level --in the first case by Eq. (I) on the assumption that the flow was laminar with a linear law of resistance, and in the second by Eq. (2) on the assumption that the flow is turbulent; this is seen from the equations = 2LQ/~v(h ~ + %) H(1) and = 2Ql~v(h, + h,) ~77.(2)where K Z and K t are the permeability coefficients, respectively, in the case of linear and quadratic laws of motion of the flow, cm/sec; Q is the seepage through the dam, mS/sec; hl and h2 are the depths of the seepage in the initial and end cross sections of the inves...

In mountainous regions where it is usually difficult to haul in construction materials, earth dams made of local materials are the most expedient type of retaining structures. The impermeability of high dams is most often secured by creating a cutoff of low-permeability soil. In regions with high seismic activity additional requirements are imposed to assure reliability of the structures. In this case the stability of darns should be secured by mandatory consideration of factors determining both the long-term and short-term adverse effect on their behavior.The practice of constructing and operating dams shows that among the most unfavorable short-time factors adversely affecting the reliability of high dams is disruption of the continuity of the cutoff element by the formation in it of longitudinal and transverse cracks caused both by nonuniform deforrnadons of the dam during the postconstruction period and by earthquakes during operation. An underestimation of such damages when designing dams can be dangerous.The considerable adverse effect of cracks on the behavior of structures is confirmed by the published data of an analysis of the causes of earth dam damage in the USA [1]. These data show that about 40% of all such damage is due to seepage through dams, about 30% is due to construction defects, and 30% is due to unsatisfactory operation of the discharge devices. All those cases which were accompanied by a noticeable increase of seepage and the occurrence of piping are considered to be seepage-caused. In our opinion, the effect of seepage, and consequently the formation of cracks causing it, on the failure of dams was responsible in a much greater number of cases than has been recorded by investigations. Actually, it has been possible to notice the formation of cracks only in those dams where by virtue of certain circumstances these cracks were exposed and caused serious operational impairment tothe structure, and then its damage.Longitudinal cracks form usually due to differences in compressibility of the soils in the core and transitional zones, and also nonuniform temporal self-consolidation of clay, especially when the core is wetted on the upstream side during filling of the reservoir. The occurrence of transverse cracks is due mainly to nonuniform deformation of the body and foundation of the core over its length, especially under the effect of seismic forces [2]. The character and size of these cracks are determined by a number of factors, including the canyon outline at the dam site, height of the structure, and deformative properties of the soils in the body and foundation of the core. Longitudinal cracks can have only an insignificant adverse effect on the operation of the core as a cutoff element, and therefore they can be neglected when calculating seepage through it.The most dangerous disruption of the continuity of the core occurs with the appearance of transverse cracks, which propagate in a direction parallel to the seepage movement through the core and threaten to produce the direct communic...

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