Full-scale investigations of seepage in an experimental blast-fill dam

Abstract

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...