ABSTRACT:

Joint shear behavior is analyzed in relation with profiles 2D statistical description, 3D statistical modelling of asperities angularity, geostatistical analysis and krigeage modelling to detect superposed structures and restitute surfaces topography of a joint roughness morphology on replicas of a natural fracture submitted to direct shear tests performed under various normal stresses and stopped at defined shear displacements. The shear processes and progressive degradation on the replicas joint surfaces as well as their evolution are evaluated through measurements of the damaged areas using image analysis. The evolution of the size and location of the damaged areas are analyzed in relation with normal stress for given shear displacement.

RÉSUMÉ:

Le comportement d'un joint en cisaillement est analyse en fonction de la description statistique 2D des profils, de la modelisation statistique 3D de l'angularite des asperites, de l'analyse geostatistique et du krigeage permenant de detecter la superposition de structures et de restituer la topographie des surfaces de la morphologie de la rugosite du joint, sur des repliques d'une fracture naturelle sollicitees en cisaillement direct sous diverses contraintes normales et pour des deplacernents en cisaillement definis. Les mecanismes de cisail- Iement et la degradation progressive des surfaces du joint sur les repliques, ainsi que leur evolution sont evalues en mesurant les aires endommagees à I'aide de la technique d'analyse images. L'evolution de la dimension et de la localisation des aires endommagees sont analysees en fonction de la contrainte normale appliquee pour des deplacements en cisaillemcnt definis.

ZUSAMMENFASSUNG:

Das Verhalten von Kluftscherung wird analysiert in Benzug auf 2D-statitische Beschreibung der Profile, 3D-statitische Modellisierung der Winkel von Asperiten, geostatitische Analyzen und Krigeagemodellierung, um aufeinandergereihte Strukturen einer rauhen Kluftmorphologie auf Bausteinmodelle eines natuerlichen Bruches, festzustellen. Scheversuche an diesen Modellisierungsversuch wurden unter verscheidene normale Spannungen ausgefuehrt und bei hestimmten Scherdeplacierungen angehalten. Der Scherungsprozess und progressive Degradierung der Kluftflachen des Bausteinmodels wurden in den gestörten Zonen durch lmageanalysierung ausgewertet. Die Entwicklung der Grösse und genaue Stellung diesel' Störungszonen wurden analysiert in Bezung auf Normalspannung fuer einen bestimmten Scherungswert.

1 INTRODUCTION

The prolific literature on characterization and behavior of single, irregular rock joints submitted to various normal and direct shear loading conditions, to evaluate the needed mechanical and hydraulic parameters In hydromechanical stability analysis of workings in fractured rock masses (Stephansson 1985; Barton & Stephansson 1990; Myer et al. 1995; to cite only the three organized symposium of the ISRM commission on rock joints) show their inextricable complex behavior and characteristics. These numberless research works on various rock joints problems confirm Scholtz (1990) statement that there is no constitutive law for friction quantitatively built upon micromechanical framework because of the complexity of shear contacts, the topography of contacting surfaces and the evolving surfaces topography during sliding. A recent review of the literature on rock joints testing and modelling (Stephansson & Jing 1995) pointed out that there is still a large number of problems to solve before having an overall understanding of the phenomenon, particularly the roughness morphology and the difficulty of its characterization and modelling. In this paper, an approach is reviewed for geometrical description of joint surfaces morphology on the basis of a 3D statistical description and modelling. A contribution to the characterization of damaged areas in relation with shear displacement under constant normal stress is also presented, in which the evolution and geometrical characteristics of the damaged zones are evaluated in relation with the normal stress magnitude.

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