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Notes: Conclusions 1. Equation (3) is recommended for determining the design value of the coefficient of strength fst of rock en masse. 2. In engineering-geologic reconnaissance practice, use should be made of the classification presented in Table 1, in order to gather data for changing over to the new index of soundness of rock en masse.

Notes: Conclusions 1. The chamber walls are stable under static loads. The horizontal displacements of the rock walls of the chamber, which during the period from April 1975 through September 1976 reached a maximum value of 15 mm, are diminishing with time and indicate pressure release of the rock mass due to excavating the chamber cavity. Additional support is not required. The analysis and the character of the displacements based on the available data do not give grounds to assume disturbance of the stability of individual large rock blocks in the chamber walls. The 1977 data indicate stabilization of the wall deformations and confirm the correctness of the conclusions made. 2. It is necessary to continue regular observations of the deformations of the anchors during operation of the pumped-storage plant units for checking the stability of the chamber walls under the effect of dynamic loads.

Notes: Conclusions 1. Improvement of the layouts and designs of underground hydraulic structures by combining the functions of tunnels, using designs involving the surrounding rock in work, and also the use of precast structural elements is an important reserve of scientific and technological progress in underground hydrotechnical construction. 2. It seems expedient to use the described designs in objects that are being designed and to organize and conduct investigations to substantiate these designs for particular objects, including future ones. 3. Since the majority of progressive designs are possible only if a smooth contour of the workings is provided and overbreak of rock and overplacement of concrete bring harm, it is necessary without delay to develop and introduce an effective technology of smooth blasting in Soviet underground hydrotechnical construction for the most characteristic engineerhing-geological conditions.

Notes: Conclusions 1. The use of a yielding structure of the arch of the generator hall provides reliable support of the roof under conditions of large tectonic stresses. 2. Compared with the more technologically efficient but more material-consuming rigid structure according to the technical design, the proposed structure makes it possible to obtain a technical-economic effect due to a reduction of the volume of works on rock excavation and underground reinforced concrete in connection with reducing the thickness of the arch to 0.7 m. At present the space under the arch of the generator hall of the Rogun hydrostation is already being driven and works are underway on concreting the arch of the proposed and investigated combined structure (according to variant 6).

Notes: Conclusions 1. With respect to the length of the route, depth, engineering-geological conditions, presence of thick zones of faults, gas-dynamic phenomena, quite considerable inflows of geothermal waters with a high temperature, and especially large rock pressure, the Arpa-Sevan tunnel numbers among unique structures. 2. The main causes of the formation of damages are the engineering-geological conditions related mainly to the large depth of the tunnel and changes in the properties of the rocks when they are saturated with water, as well as to disturbance of the hydraulic regime of operation of the tunnel. 3. When designing the tunnel it was impossible to accurately predict changes in the physical and mechanical properties of the rocks, which entailed a decrease of their strength and deformability and an increase of movements and rock pressure on the lining. 4. Damage of the tunnel lining after operating for 5 years on a length of less than 10% of the total length (in this case the section of total reconstruction of the lining is only 5% of the tunnel length) is not an extreme phenomenon under the indicated conditions. The works performed on reconstructing the lining make it possible to evaluate the further operation of the tunnel as completely reliable, since the 5-yr operation, which can be regarded as a large-scale experiment, revealed the weakest places. 5. When designing analogous structures the value of the characteristics of the ground should be determined with consideration of a change in its properties upon saturation with water under pressure on the basis of investigations according to specially developed instructions. It is also necessary to develop a program of lining calculations taking into account the time factor and continuously varying properties of the medium during tunnel operation. 6. The experience of operating the Arpa-Sevan tunnel confirmed the recommendations of par. 1.5 of building code SNiP 2.06.09-84 “Hydraulic Tunnels,” that the main tunnels intended for constant passage of water during operation of hydrostations, reclamation systems, and water-supply systems should be equipped with monitoring and measuring instruments for evaluating the condition of the tunnel lining, ground surrounding it, and hydraulic and seepage regimes. The readings of these instruments should be led out from the tunnel to control boards allowing an evaluation of the state of the structure at any time. It is necessary to provide automation of the operating regime of long free-flow tunnels not calculated for pressure from the internal water pressure.

Notes: Conclusions 1. The majority of linings of hydraulic tunnels during their operation receive various damages — considerable leaks of water from the tunnels are observed, the working and technological joints open and large cracks form in the linings, the surface roughness increases, and the linings are destroyed in individual sections of the tunnel. As a result the capacity of the hydrostation decreases, and in individual cases emergency situations related to loss of stability of the tunnels and sliding of the mountain slopes are created. 2. The recommendations given in the present article permit improving the quality of linings and, to a considerable extent, preventing their damage during operation of hydraulic tunnels.

Notes: Conclusion The operating experience gained with the diversion tunnels of the Charvak, Nurek, and Toktogul hydroelectric schemes confirmed their high efficiency under severe hydraulic conditions, involving the conveyance of high-velocity discharges carrying abrasive sediments. It should be noted that the actual operating periods of the tunnels significantly exceeded the design durations. The expediency of adopting a horseshoe cross-sectional shape for large diversion tunnels operating under pressure, was also verified. At the same time, the operating record of these large size unique tunnels, the first in construction practice, has demonstrated the possibility of reducing the materials required for their construction, thus enabling their construction time and cost to be reduced, as well as the labor input in building similar tunnels of large cross section.