The well understood tendency of placing the systems of underground structures of powerplants in the rock masses with favorable geologic conditions rarely can be realized in practice. Generalization of insitu and model data obtained for already completed projects (in our case the powerhouse of Inguri powerplant) is the best basis for choice of a numerical method and model to be used during the design stage of a new structure.
Das Bestreben komplexe unterirdische Bauwerke von Wasserkraftwerken in Bereichen von Bergmassiven unter guenstigen ingenieur-geologischen Bedingungen zu errichten, kann in der Praxis nur selten realisiert werden. Die Verallgemeinerung von in-situ Werten und Ergebnissen aus Untersuchungen an Modellen, die durchgefuehrt wurden fuer bereits bestehende und im Bau befindliche unterirdische Maschinenraume von Wasserkraftwerken machte es maglich, rechnerische Prinzipien zur Begruendung von Vortriebsschemen und Konstruktionen zur Verankerung des Systems groBer, dicht beieinander angeordneter Hohlraume der zu projektierenden Kavernen zu verwenden.
La tendance a construire des complexes souterrains de centrales hydroelectriques dans des massifs rocheux dans des conditions geologiques favorables peut être concretisee rarement dans la pratique. La generalisation des donnees in-situ et des resultats des etudes des modeles provenant des projets qui ont ete deja executes (dans notre cas, les salles des machines souterraines de la centrale hydroelectrique Inpri) est la meilleure base de choix d''une methode numerique et d''un modele devant gtre utilises durant la phase de dimensionnement d''une nouvelle structure.
Design of the support systems for the large-span underground openings is an intricate problem without a sole solution. Systems of caverns for underground hydraulic powerplants usually include openings for powerhouse, transformer hall, valve chambers and Sometime underground surge shafts or reservoirs. In some cases this caverns are at sufficient distances from one another and for layout at shallow depths the trans- former hall is placed usually on the ground level, so each cavern may be regarded separately from other openings, but quite often the analysis has to be made for the whole system of underground structures. The difficulties arise from the existence of access adits, ventilation and cable shafts, draft tubes, eic. From the analyst''s point of view this is a typically three-dimensional problem which only in rare cases can be solved as a two-dimensional one. Sole reliable source of information on the stress-state of the structure and surrounding rock mass is in situ measurement. Regretfully this kind of data is available only during and after the construction process takes place and is not at hand during the design stage. One can use only the data from the analogous structures already in operation or apply to mathematical or physical models. Further parallel analysis of data obtained from models and in situ during and after construction provides the basis for drastic improvements of models in use and higher level of design for new projects. (Figure in paper)
At the Moscow Institute of Civil Engineering (MICE) investigations for the Inguri underground powerhouse were initiated by Eristov et al in 1969 (1972,1974). The cavern (Fig. 1) is 126 m long, 21.8 m wide and 52.3 m high. The support consists of a reinforced-concrete arch with suspended crane beam-walls. The arch axis is a circular arc with radius of 14.05 m with a central angle of 1200. The arch thickness at the crown and that of the crane wall$ is 1.3 m and the arch thickness at the abutments is 2.23 m. The height of the opening supported by the concrete arch and the crane beam-walls is 13.33m. The cavern is located in thicklayered medium-jointed limestones. The dip of the rock strata is 30–400 and the rock shows considerable anisotropy. Preliminary geological investigations gave the values for the Young''s modulus in the direction along＿ the strata E = 8000 - 10000 MN/m4 and in perpendicular direction E = 6000 - 8000 MN/111. For model analysis materials prepared of plaster and grounded limestone mixtures were used. The MICE has gained quite a reputation for physical static and dynamic modelling of different kinds of hydraulic structures (dams and foundations, tunnels, etc.) and model materials were selected from an abundance of mixture recipes. Wide-ranging test program was carried out for the determining both the physical-mechanical characteristics of the model materials and that of interlayer joints. Several two-dimensional models were analyzed for cases of isotropic and anisotropic jointed rock mass. For isotropic homogenous conditions the model was made by direct pouring of the model material mixture into the 1.8x1.8x0.2 m rigid steel framework and subsequent drying. Anisotropic jointed and layered rock mass was modelled either by pouring different model materials in order to make thin layers with different properties or by assembling the model from prefabricated bricks made of dryed model material. In some models granular paraffin was used to reduce interblock or interlayer friction.