This paper describes how rock displacement meters were used to measure deformations in the rock forming the foundations of an arch dam. From the measurements, an effective rock modulus as experienced by the dam is deduced and compared with the estimate made using plate jacking tests in four galleries of the foundation. Measured prototype deformations of the foundations were predictable, and even reflected the weakening effect of fractured rock in a known faulted zone. Values from jacking tests were a good measure of the foundation modulus, while a seismic value obtained in similar rock was high by a factor of two. It is concluded that correlated measurements of this kind allow designers to build up confidence in their simplified models of reality.
Cet expose decrit comment des "elongamètres" mesurant la deformation de la roche ont ete employes pour mesurer les deformations de la roche formant la fondation d'un barrage en voute. En consequence on a deduit le module d'elasticite effectif dont on avait fait l'experience dans le barrage et on le compara aux evaluations faites en utilisant des essais au verin dans quatre galeries de la fondation. On a trouve qu' on pouvait predire les deformations mesurees du prototype, et que les valeurs obtenus dans les essais au verin correspondaient favorablement au module de la fondation. On a conclu que les mesures correspondantes de cette sorte permettent a l' ingenieur d'avoir une plus grande confiance dans ses modèles simplifies de la realite.
Diese Abhandlung beschreibt, wie Messgerate fuer Felsverformung benutzt wurden, um Verformungen in der Felsgruendung einer Bogentalsperre zu messen. Aus diesen Messungen wird ein von der Talsperre erfahrener Modulwert abgeleitet und mit derSchatzung verglichen, die anhand von Belastungspruefungen an vier Stellen der Felzgruendung gemacht wurde. Es stellte sich heraus, dass die Verformungen in der Gruendung vorauszusehen waren; diese reflektieren auch eine Schwachung in einer bestimmten Störungszone. Die aus den Belastungspruefungen gewonnenen Werte erwisen sich als gutes Mass fuer die Gruendungsmodul, wahrend die Werte aus seismischen Versuchen doppelt so hoch waren. Hieraus lasst sich schliessen, dass derartige Messungen den Ingenieuren erlauben, ein Vertrauen dafuer zu entwickeln, dass ihre vereinfachten Modelle den Bedingungen der Wirklichkeit entsprechen.
An arch dam is a highly hyperstatic structure; its analysis makes use of simplifying assumptions about the paths the imposed loads take in reaching the foundation, and further simplification about how they interact with the dam shell. The overall stability of the foundation is dependent upon the manner in which the geological jointing and faulting is oriented with respect to the dam thrusts; this is not considered in this paper, which is concerned with the movement of the foundation due to the loads imposed on it by the dam forces. The dam-foundation complex must, of course, be designed as a whole but the foundations are here separated from the dam which is considered as the device loading the foundation; the purpose of the separation is to focus attention on the single most important parameter which characterises the foundation when treated as a homogeneous mass, namely, the rock deformation modulus, ER. Whatever method might be used to design the dam, the designer eventually has to decide what value to adopt for the effective rock modulus, in order to work out the deformations at the dam-foundation interface. Calculations for Gordon Dam by Giudici et al, (1975) have indicated the small percentage change of stress in key areas of the dam due to even large variations in modulus. An estimation of deformation modulus can be made by careful geological observations or ultimately by some direct measurement. This is where the helpful insensitivity of the shell to foundation movement is partly negated by the impossibility of sampling, by any measuring technique, more than a small portion of the total loaded area. Even when sites are carefully chosen as being representative of the foundation, small scale plate tests, for example, suffer from the inherently small bulb of pressure or small volume of material which is being sampled and stressed. The dam on the other hand will feel the integrated effect of foundation imperfections to greater depths than.can be conventionally sampled. It is interesting, therefore, to measure the actual foundation deformation and thus to deduce the foundation modulus the dam "feels" for comparison with the estimated values.
Gordon Dam is a double curvature arch dam set in a narrow gorge of the Gordon River in the south west of Tasmania. The dam is part of the system of the Gordon Power Scheme described by Thomas (1971). The dam is 140 m in height, 200 m in crest length and varies in thickness from 1m at the crest to 18 m at the base. The main geometric feature of the valley is the marked asymmetry between the left and right abutments.
