For a long time "Hydroproject" Institute (Moscow) is carrying on observations over deformation processes at the foundation of the Inguri dam (Western Georgia), and the geophysical methods are being used. It has been found that each stage of the project construction and operation corresponds to a certain type of alteration in velocities of elastic waves in supersonic and seismic frequencies range. The reasons of the observed alterations of the velocities, as well as possibilities of usage of geophysical data for quantity evaluation of deformation processes and their forecast are discussed in this paper.
L'institut "Hydroproject" (Moscou) fait depuis longtemps des observations sur les processus de deformation dans la fondation du barrage-voûte d'Ingouri (Georgie Ouest) en utilisant les methodes geophysiques. On a constate que chaque phase de construction et d'exploitation de l'amenagement correspond à la variation certaine des vitesses d'ondes elastiques dans les gammes de frequences ultra-sonores et sismiques. Les raisons des variations observees des vitesses, ainsi que la possibilite de l'utilisation des donnees geophysiques pour la determination quantitative des processus de deformation et pour la prevision des ces derniers, sont discutees.
Seit langerer Zeit werden vom Institut Hydroprojekt (Moskau) die Deformationvergaange im Felsuntergrund der Bogenstaumauer an der Wasserkraftanlage Inguri (Westgrusien) mit geophysikalischen Verfahren beobachtet. Es ist festgestellt worden, daβ jeder Bauund Betriebsstufe der Wasserkraftanlage ein bestimmter Charukter der Geschwindigkeitsanderung elastischer Wellen im seismischen und Ultraschall-Frequenzbereich entspricht. Die Ursachen der beobachteten Geschwindigkeitsanderungen sowie die Möglichkeiten der Anwendung der geophysikalischen Daten zur qualitativer Einschatzung der Deformationsvorgange und deren Vorhersage werden erörtert.
The Inguri hydropower scheme with its arch dam, 271.5 m high, which has been built under complicated engineering and geological conditions, operates successfully during several years, and is a unique project. For the said period of time the water reservoir level reached, and not once, its maximum design elevation, while an amplitude of its fluctuations achieved 100 m. During this period significant techno-genetic loads transferred upon the structure footing and those loads have changed the original strain-deformed state of the massif and have caused development of various deformation processes there (Savich et al. 1979; Savich et al. 1983). To keep under control the mentioned processes a system of comprehensive field investigations has been created at the dam section and a component part of the system are the regime seismo-acoustic observations (Savich et al. 1979). Such investigations with usage of elastic waves in seismic (f ≈ 100 Hz) and ultrasonic (f ≈ 30–50 KHz) range of frequencies were being carried on at the Inguri HPS already more than 10 years, and thanks to them some certain regularities in alteration of the massif properties have been found in a zone of its interaction with the dam at different stages of construction and operation of the structure. The received conclusions in many aspects are based upon the results of a quantity geomechanical interpretation of observed space-time variations of velocities of the elastic waves (longitudinal Vp and lateral Vs) of the seismic (VC) and ultrasonic (Vy3) ranges of frequencies. Transition to the level of quantity estimation of processes which go inside the massif demands further development of the geomechanical models. The possible reasons for velocities alteration and methods of quantitative interpretation of the data found at the regime seismoacoustic observations are discussed in the present paper on the basis of an analysis of the measured variations in time of the velocities VC and vy for one stretch of the left-bank abutment of the arch dam.
The massif of the left-bank abutment of the arch dam is represented with a strata of thick-layer Low-Cretaceous limestone within the limits of which several differently orientated systems of tectonic and lithogenetic fractures are developed (Fig. 1). The mostly spread are the fracture of system I having modulus of jointing M =2.5–10, of system II with M = 2–5, of system III with M = 0.2–0.3, of system IV with M =0.2–0.25, and as well of systems V and VI with modulus M < 0.1. The filler of the joints is a various one, mainly it is fault gouge and carbonate landwaste; a part of the joints has no filler at all (Dzhigauri 1980). The massif is subjected to significant tectonic stresses, and the maximum compressive stress б3 is ≈ 20–30 MPa, it is horizontal, and oriented along the Inguri river valley. At the subsurface part, down to some 50–60 m, the massif is unloaded due to unexpected decrease of the vertical component бz = бI =γh, where: γ - volume weight, h - thickness of the above laying rock (Savich et al. 1981).
