Works on the construction of the foundation pit for the dam of the Kurpsa hydroelectric station began following the completion of the temporary diversion tunnel and damming the Naryn River [i].After the rock was excavated in the side cuts for the dam, excavation began in the channel part of the pit, where in an extremely short time (1.5-2 months) it was required to excavate about 60,000 m 3 of earth. The dimensions of the dam pit are: width ii0 m and length 90 m. Immediately adjacent to it is the ll0gm wide, ll5-m-long foundation pit for the powerhouse.Upper Carboniferous flysch deposits, represented by interstratified sanastones of strength group VIII with respect to the Construction Norms and Regulations (SNIP) (up to 75%) and argillites of group VII (up to 25%) occur in the base of the pits. The rock surface in the channel is uneven. There were a largenumber of grooves and individual depressions filled with fluvial deposits with various particles sizes. The thickness of the alluvial deposits reached 5 m.The foundation rocks were broken by various tectonic joint systems and bedding joints. With respect to the degree of fracturing the rocks belong to the II category (severely fractured, medium-block) according to the provisional classification [2]. The rocks in the channel are severely waterlogged. There was flowing water (recharge from the upper pool) in the rock mass over the entire section being excavated. The plan of the pits is shown in Fig. i. The contract design called for loosening the near-contour layer by 105-mm-diameter borehole charges with a 1.5 m-thick protective layer being left. The protective layer was to be finished in two levels: the upper 1-m-thick level with loosening by means of blasthole charges with manual pneumatic drilling and the lower 0.5-m-thick level by means of picks.However, it was impossible to accomplish the design scheme, since even in stretches of the river where the rock outcropped the blastholes and even the 105-mm-diameter boreholes, drilled by rigs with a submersible compressed-air drill (NKR-100M), after extracting the drilling tool either collapsed or were very quickly filled with sand and cuttings owing to the strong inflow of water. An intense technology of excavation with loosening of the rocks by charges of 130-mm-diameter sticks of explosives in holes bored by BTS-150 rigs was developed.To protect the base of the pit from destruction the holes were drilled short so that the boundary of the explosive disturbance of the natural state of the mass did not exceed the limits of the design outlines of the pit.The size of the zone of disturbance was determined by the method developed at the AllUnion Trust for Special Hydraulic Engineering Works (Gidrospetsproekt) [311 The calculated depth of the zone of penetration of blast deformations into the mass was 12 charge diameters. In conformity with this, the bottom of the charges was 1.5 m from the base. To determine more accurately the effect of the explosion into the mass, experimental clearing to the undamaged rock was perfor...

The problem of the directed blast on the Burlykiya River (Fig. i) was to form a rock pile which would model the Kambaraty Dam. The working design of the blast took into account the microrelief features of the gorge.Determination of the blast outline and construction of the pile profiles were carried out by the method of parallel sections.A linear charge arrangement was adopted.The lines of least resistance (LLR) for individual segments of the charges were determined graphically.Depending on the designed dam section, the LLR of the main charges for the left and right banks amounted to 7-40 m and 9-24 m, respectively. The values of LLR for auxiliary charges ranged from 8 to 22 m~The charge per meter of the gallery was computed fromwhere K is the computed consumption of explosive, with an adopted value of 1.8 kg/m 3, assuming granular granulite 79/21 was to be used; w is the line of least resistance, m; n is an index of the action of the blasts (for the main charges, n was taken to be 1.1); and e is the power coefficient.Where LLR exceeded 25 m, a correction Vwf~25 to the embedment depth was applied.For the explosive, granulite "M" (power coefficient e= 1.12) was adopted; this was loaded into the galleries by pneumatic chargers.Having regard to the great mass of explosive supplied, the complex topography, the limited time available, and the stricter requirements for safe work, a separate design was prepared for the charging operation.A short-delay detonation of the charges was proposed in the following pattern: on the right bank, the first-and second-stage blasts of charge 1 (Fig. 2) and, after a 25-msec delay, those of the charge in gallery No. 4; on the left bank, the third-and fourth-stage blasts I00 msec after the charge in gallery No. i, and the charges in galleries Nos. 2 and 3 also after i00 msec.In arranging the delays, allowance was made for an overhang over a considerable area of the left bank, and also having regard to the recommendation of the Institute of Physics of the Earth (IFZ) of the Academy of Sciences of the USSR, stemming from results of small-scale modeling.The design aimed at heaving 478,000 m 3 of rock into the gorge, to form a pile some Fig. i. View of dam site on the Burlykiya River from upstream.

The Kambaraty hydroelectric scheme, currently in the design stage, comprises a homogeneous dam, two head-race tunnels, an underground power station, and two discharge tunnels. The site area extends some 4-5 km. The Naryn River here makes a sharp bend.The river valley has a somewhat asymmetric cross section, with steep banks which flatten out in the upper part of the slopes.A narrow gorge 30-60 m deep is cut into the valley floor. The abutments reach heights of 800-900 m (right bank) and 1100-1200 m (left bank) above the valley floor. The valley width above the gorge varies from 60 to 150 m, reaching 750-950 m at the dam crest level. The area is distinguished by deep dissection and considerable steepness of the exposed slopes.