ABSTRACT

Hydraulic experiments have been conducted since 1997 within a small fractured calcareous rock mass in southeastern France, at a site called Coaraze. On this reduced-scale site closing a floodgate located on a downstream spring produces repeated hydraulic loadings. Simultaneous measurements of normal deformations and pressure in several joints have provided a better understanding of the hydromechanical behaviour of such a fractured rock mass. The present paper first describes both the site and conceptual interpretation of the measurements performed. We showed that accurate measurement reproduction requires incorporating certain features: a variable normal joint stiffness, the joint vicinity (through introducing a Z coefficient), and the initial stress state. The paper then develops an original analytical interpretation of the coupled pressure-displacement measurements carried out, which reveal the high level of measurement suitability to the non-linear behaviours examined. 2D modelling, using the discontinuous code (UDEC) was used to proceed with the calibration step.

ZUSAMMENFASSUNG

Hydromechanische Experimente werden seit 1997 in einer kleinen Kalksteinmasse, das sich im Suedosten von Frankreich befindet durchgefuehrt. In diesem kleinen Standort, werden wiederholte Wasserdruck Erhöhungen durch das Schliessen eines Hahnes produziert. Gleichzeitiger Druck und normale Verformung Meßungen in mehreren Fugen haben erlaubt, das hydromechanische Verhalten einer solche gebrochene Felsenmasse besser zu verstehen. Der Artikel beschreibt zuerst den Standort und stellt die begrifflichen Interpretationen der Meßungen vor. Um die Meßungen gut zu reproduzieren ist es wesentlich, bestimmte Faktoren wie die veranderliche normale Steifheit der Fugen, die Nachbarschaft der Fugen (ueber einen ZKoeffizient) und der Spannungstand zu beruecksichtigen. Der Artikel erklart die originale Methode fuer die Druck- und Verformungs-Meßungen Interpretation und zeigt die gute Korrelation der Meßungen mit dem nicht-linearen angenommen Verhaltens der Fugen. Die numerische 2DModellierung mit dem UDEC Software ist fuer die Verkeilung der Faktoren gebraucht worden.

RESUME

Des experimentations hydromecaniques sont conduites depuis 1997 dans un petit massif calcaire fracture situe dans le sud de la France. Dans ce site de taille reduite des mises en charge repetees sont produites par la fermeture d'une vanne situee à l'aval du site. Des mesures simultanees de deformation normale et de pression dans plusieurs joints ont permis de mieux apprehender le comportement d'un tel massif fracture. L'article decrit dans un premier temps le site et presente les interpretations conceptuelles des mesures. Pour bien reproduire les mesures, Il est essentiel de prendre en compte certains facteurs tels que la raideur normale variable du joint, le voisinage du joint (par l'intermediaire d'un coefficient Z), l'etat de contrainte initial. L'article precise la methode originale d'interpretation des mesures pression-deplacements qui montre la bonne adequation aux lois de comportement non lineaire proposees. La modelisation 2D, à l'aide d'un code discontinu (UDEC) a ete employee pour le calage des facteurs.

Introduction

In order to better understand the hydromechanical behaviour of a fractured rock mass, hydraulic experiments have been conducted since 1997 within a small fractured calcareous rock mass, at a site called Coaraze situated in southeastern France (Guglielmi, 1999). On this reduced-scale site (approximately 20,000 m3), repeated hydraulic loadings are produced by closing a floodgate located on a downstream spring.

The first section of this paper is devoted to a description of the site and the measurements. The second section will focus on an analytical interpretation of the measurements performed, which serves to demonstrate the importance of incorporating a variable normal joint stiffness along with the joint environment, to be characterised by a coefficient Z and which has led to developing an original methodology for evaluating the maximum normal effective σ'ni value in the absence of water. The third section will discuss how discontinuous modelling was performed in order to calibrate non-linear behaviour.

Site and experiment description
The site

The Coaraze site is situated in southeastern France, some 25 Km north of the city of Nice. It constitutes a small Beriasien-Valanginien aquifer located on the left bank of a small valley lying in a N40 direction.

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