ABSTRACT:

The paper summarizes the results of different-scale deformation tests performed at a large number of hydraulic and other projects during the last 30 years. The analysis demonstrates that the scale factor with respect to deformation properties of rocks shows up vividly only at transition from laboratory to in-situ investigations. The attempts to reveal it at processing the results of in-situ geomechanical tests with different active volume of rock loading have not been successfull because of a large number of acting factors.

RESUME:

Dans un travail sont generalise les resultats des essais à I'echelle differente dont les proprietes de deformations, que sont realise sur grande nombre des objets hidrotecniques et d'autres pendant 30 annees derniers. L'analyse montre, que l'effet d'echelle dont les proprietes de deformation de roche clairement se manifeste seulement en traversant des essais en laboratoir à les investigations "in-situ". Relever de set effet d'echelle pendant a l'etude des resultats d'essais geomecaniques avec' volume actif differente de massif rocheux à chargement n'est pas abouti à cause de grande nombre de facteurs d'iufluence.

ZUSAMMENFASSUNG:

Die Resultaten der Deformationsforschungen von dem verschieden smaß stabs in dem Felsmassen sind zusammengefaßt. Diese Forschungen auf zahlreichenden hydrotechnischen und andere Objekten im Laufe von letzten 30 Jahren autgefuehrt waren. Die Analyse hat gezeigt, daß der Maßstabfaktor sich im Bezugauf die Gesteinsdefomlationseigenschaften bei dem Übergang von den labormaßigen Versuchen zu den Felduntersuchungen klar offenbart. Die Herausgestellung dieser Faktors mittels Bearbeitung der Resultaten von dem geomechanischem Feldversuch mit verschiedenen aktiven Gesteinsumfangen mißlungen ist, da die Menge der anderen entscheidenden Faktoren zu groß war

1 INTRODUCTION

Modulus of deformation is the most widespread characteristic of rock masses used for designing various engineering structures: dams, tunnels, large chamber excavations, bridges, etc. By the present time a considerable amount of factual data for its determination has been accumulated and various correlation relationships connecting modulus of deformation with engineering geological and other parameters have been proposed. In the sixties and seventies plate bearing tests carried out in underground excavations by concrete plates usually l.0xl.0m in size were the most frequent type of in-situ investigations. In most responsible cases tests were conducted in pressure chambers and somewhat later tests of radial loading in cylindrical chambers 1.5 - 2.0m in diameter were carried out. The mentioned types of investigations are rather labour consuming and in this connection in the following years tests with the use of flat jacks and particularly pressuremeter (dilatometer) tests in boreholes appeared more frequent (the latter tests on account of their efficiency and a small scale may be related to proximate investigations). However at performance of pressuremeter tests and tests with small flat jacks a question always arises about reliability of the obtained results because of a small active volume of the rock involved in this tests. The problem of reliability of this or that type of investigations is closely connected with the problem of the scale factor The analysis of the results of plate bearing tests with different area of loading performed by specialists of" Institute Hydroproject " at a number of hydraulic projects demonstrated that with an increase of dimensions of the plate both a decrease and an increase of modulus of deformation of the rock mass may take place (Iofis and Rechitski 1993). In this case for high-modulus rock masses (by convention E>8000 MPa) a decrease of value E with an increase of the loading area F takes place normally and at small moduli of deformation of rock masses relationship E=f(F) is mainly of an increasing nature (see Figure 1).

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