It is a well-known fact that the economic design of linings for hydraulic delivery tunnels calls for maximum utilization of the load-carrying capacity of the enclosing hard rocks. In present design practice, such rocks are taken to be elastic, instantaneously deformed media, and stresses in the lining are determined by the theory of elasticity. At the same time, investigations of deformation properties of hard rocks in situ show that most of such rocks, under continuous load, are capable of different degrees of continued deformation, i.e., of creep. For this reason, the actual state of stress in the lining may substantially differ from that computed from the theory of elasticity.This article integrates the results of special fietd studies of creep in hard rocks at the V. V. Kuibyshev MISI (Moscow Civil Engineering Institute) * and presents a method of stress state calculation for delivery tunnels in creepprone rocks.To determine slow deformations in various types of hard rocks, special experiments with rectangular concrete plates 1 m z in area were carried out in galleries at the sites of the Kirovsk and Andizhan dams of the Uzbek SSR (Fig. 1).Rock creep was studied at increasing and decreasing pressures on the plates. Analysis of the experimental data shows no substantial qualitative difference in the reaction of the rock surfaces in question (chlorite-sericite schists, black shales, stratified and massive sandstones) to the local static load. This makes it possible to consider the investigation results as valid for the total rock mass. We now turn to the principal deformations in these rocks upon initial loading. Figure 2 shows typical mean deformation (S) --mean pressure (p) graphs reflecting the rock surface behavior as the pressure is applied to the plate in increments. These graphs show that the enveloping function S = f(p), represented by the dashed line in Fig. 2, is generally nonlinear, at both increasing and decreasing pressures. For the rocks under study this function is substantially nonlinear as a rule in a relatively narrow range of increasing pressures, fluctuating from 2.5 to 10 kg/cm 2, depending on the rocks. At higher pressures, up to Pmax = 40 kg/cm z used in the experiments, the enveloping function can be taken as linear. The deviations from linearity are slight and irregular; they may be due to scatter of the experimental data.

In 1962 we offered an approximate method for the computation of pressure tunnel linings subject to internal pressure in anisotropic, orthotropic elastic media [1]. * In this method it is assumed that the reaction coefficient and radial deformations along the lining perimeter change according to the sinusoidal law.Art e = ay + (ax--Ay) sin eThese relationships reflect very roughly the real change of the reaction coefficient andradial deformations and lead to difficulties in the evaluation of errors in the computation of final results. Particularly, passing from one quadrant to another on the OY axis, these formulae give sharp changes in k 0 and Auo which cannot occur in reality. Besides, when the sinusoidal law is followed, the computation results depend on the direction of the coordinates in respect to the direction of the stratification.Computations show that more reliable results are obtained if the OY axis is parallel and OX axis normal to stratification and ky > kx. Regarding deformations, as was shown by the results of research conducted by the Prof. Kujunzic in the tunnels of Mavrove and Goiakhydroelectric plants in Yugoslavia [4],the assumption of the ovoidal form of the deformed ring [forrnula (6)] is also not justified and the deformation diagram may have a more complicated form.

In connection with the construction of the pressure tunnel of the Ingurski hydroelectric station with a thin concrete lining and deep strengthening grouting, of interest are data from foreign practice of tunnel construction [1].The tunnel of the Ingurski station is 16.5 km long, inside diameter 9.5 m, and head to 16.5 technical arm. It runs through thick-laminated, jointed Barremian limestones with steeply sloping layers characterized by Protod'yakonov's strength coefficient ] = 6-8 and coefficients of specific elastic resistance of 700 kg/cm 2 along the bedding and 300 kg/cm 2 perpendicular to it.Percolation rates into the rocks are about 6 liters/see per 1000 m z of the tunnel at a pressure of 1 technical arm.The tunnel lining consists of a thin equalizing concrete facing, 0.5 m thick, with grouting of the rock through 17 6-m-deep boreholes around the perimeter under a pressure of up to 30 technical arm. The spacing of the boreholes along the tunnel is 3 m. Grouting is done in three stages with an increase of the grouting depth and pressure in each stage.Preliminary investigations were carried out in an experimental drift which showed that the planned type of lining with grouting is completely satisfactory from the standpoint of deformation and percolation properties of the rock around the tunnel (increase of the coefficient of resistance by 2-4 times with its equalization about the contour and an almost 15-fold decrease in percolation). The description of the lining of the Ingurski tunnel and experimental investigations were published earlier [2-4].Analogous linings were made in the tunnel of the Roselan-Bati hydroelectric station in France and Festenniog hydroelectric station in England [5]. The diversion of the Jansen pumped-storage plant in Bavaria [6] also has tunnels with a concrete facing without reinforcement stabilized with high-pressure grouting.Construction of the Tunnels of the Jansen Pumped-Storage Plant in Bavaria. The 1640-m-long Weinberg tunnel has a diameter of 3.5 m and design internal pressure of 18 technical arm. The 1319-m-long Reisach tunnel has a diameter of 4.9 m and design internal pressure of 23 technical atrn. The concrete lining of both tunnels ( Fig. 1) is 40 cm thick. Both tunnels run through tectonieally disturbed and partially weathered gneisses. It is interesting to note that the minimum depths of both concrete-lined tunnels are much less than the figure 0.5P required by our regulations: 65 m or 0.28P in the Reisach tunnel and 50 m or 0.27 P in the Weinberg tunnel.Grouting was carried out through 12 3.5-and 4.5-m-deep boreholes in each tunnel section under a pressure of 40 technical atm. Grouting was done simultaneously through 28 boreholes. Before grouting, all boreholes were flushed with drilling fluid at a pressure of 40 technical arm. A pure, finely ground cement grout prepared in highspeed mixers was used for grouting.

The widths of excavations of underground hydroelectric stations presently reach 34 m and the height in some cases 60 m; the volume of excavation of the generator rooms exceeds200,000 m s (for example, the Churchill Falls hydroelectric station and theRoncovalgrande pumped-storage plant). Tunneling speeds are increasing simultaneously. Thus, the generator room of the Zekingen pumped-storage plant in West Germany (22.6 X 33.2 • 162 m) was completely excavated in 14 months, the generator room of the Portage Mountain hydroelectric station in Canada (26.0 X 40.0 • 270 m) was driven in 16 months [6, 7], the generator room of the presently largest Churchill Falls station (24.0 • 48.0 • 296.5 m) was excavated in 15 months [7].As construction experience shows, the stress and strain on the structures of underground hydroelectric stations are affected to a considerable extent by the methods and rates of excavation in addition to the engineering-geologic conditions and size and shape of the structure. Full-scale investigations abroad on underground stations being constructed and in operation show that considerable displacements of walls occur in large excavations. These displacemenu, if they are not taken into account in the plans, lead to overstress and in some cases to considerable deformations, which involves expensive works on sealing cracks, straightening crane tracks, strengthening load-carrying structures, additional anchoring, etc. The experience of constructing the Poatina, Miranda, Tumut-1 and 2, Murray-1, and other stations showed that it is necessary to reexamine both the designs and methods of excavating large underground hydroelectric stations with consideration of the possible development of deformations. The data on the designs and technological characteristics of a number of large underground stations are given in Table [ 1, 3, S].

Participating in the conference were eight special sections; the themes covered by some of them were devoted to questions associated directly with the construction of hydraulic structures. In response to requests from readers, the editors decided to publish reviews of the work of these sections. The article by V. S. ~ristov and L. N. Rasskazov published here is devoted to the work of Section No. 3, which examined the problems of design and investigation of earth and rockfill dams. The work of other sections will be covered by articles in subsequent issues.The construction of earth and rockfill dams is taking place very rapidly over the whole world; these types are much more likely to be adopted than concrete dams, including at sites with complex geologic conditions, and in many cases they are cheaper to build than any form of concrete dam. This explains why, for example, out of the several hundred dams built in the USA in recent years, nearly 90% are of the earth or earth and rockfill type with clay cores; in Canada over 60% of the total are of embankment construction. In the USSR more than 150 dams of this type exceeding 25 m in height are either completed or under construction, including the following, which were either recently built or are nearing completion (heights given in parentheses): Vityui (75 m Many earth and earth and rockfill dams constructed recently in various other countries are also of great height (see Table 1).The volumes of these dams amount to tens of millions of cubic meters. Therefore, whereas heretofore no difficulties of a theoretical nature arose during the construction of relatively low dams of this type, great heights and volumes introduce very serious and important problems, many of which are not completely solved. Their correct solution is a matter of exceptional importance to modern dam construction, and here we first come face-to-face with problems in soil mechanics. It was precisely for this reason that a special section was set up at the 8th Conference, devoted to the design and investigation of earth and earth and rockfill dams.The following are the main problems: 1) stability analyses of dams, taking into account the influence of pore pressure in the cores and membranes of rockfill dams and in the body of homogeneous earth dams; 2) computation of consolidation of clay cores and membranes; 3) determination of the stressed state of dams and their deformation, taking into account the sequence of construction; 4) clarification of the laws governing the interaction of cores and membranes with the supporting prisms; 5) investigation of measures for preventing the formation of cracks in cores and membranes; 6) seepage calculations and investigations, including possible cracking in the cores and membranes, and the stability of membranes against piping; 7) investigations of seismic effects on the stressed state and deformation of dams and on their stability; 8) investigations of the strength, deformational, and seepage characteristics of the materials used in the dam construction; 9) i...