ABSTRACT:

A multi-disciplinary approach was adopted for the characterisation of a rock volume at the Äspö HRL utilised for an excavation disturbed zone (EDZ) experiment which was performed to enhance the understanding of the properties of the disturbed zone surrounding a drift and their dependence on excavation methodology. Two parallel drifts were excavated, one using a TBM and the other by drill and blast methods and an extensive suite of measurements were conducted using different investigation methods before, during and after excavation of the drifts. The methods used covered both remote sensing, geophysical techniques and physical investigation procedures and illustrative results are presented. The data were integrated with information from the regional geological setting of the Äspö area and will be utilised to develop an integrated model for the rock volume which will be used in a validation test.

RESUME:

Une approche multidisiplinairea ete adoptee pour la caracterisation d'un volume rocheux au HRL d' Äspö utilise pour une experience concernant l'EDZ (zone perturbee par l'excavation), realisee pour ameliorer la comprehension des proprietes de la zone perturbee autour de la galerie, ainsi que l'influence des methodes de creusement sur ces proprietes, Deux galeries parallèles ont ete creusees, l'une avec un tunnelier (TBM) et I'autre par foration-tir, et un large eventail de mesures, utilisant differentes methodes d'investigations, ont ete mises en oeuvre avant, pendant et après les creusements. Les methodes ont concerne a la fois des mesures à distance, differentes techniques geophysiques et caracterisations physiques. Les resultants des caracterisations sont ensuite presentes, Les donnees eclairees par les connaissances du cadre geologique regional d' Äspö ont servi de support au developpernent d'un modèle integral du volume rocheux, utilise pour les modèles et pour valider les observations.

ERGEBNIS:

Das durch Vortriebsarbeiten gestörter Gebirge im Äspö HRL wurde multidisziplinar untersucht, um die Eigenschaften des durch die Arbeiten beeinflußten Gesteinskörpers in Abhangikeit Von der Vortriebsmethode zu beschreiben. Zwei parallele Stollen wurden aufgefahren. Der eine wurde durch eine Tunnelbohrmaschine, der andere in Bohr- und Sprengtechnik vorgetrieben. Vor, wahrend und nach dem Vortrieb der Stollen wurden umfangreiche Messungen durchgefuehrt. Es wurden Fernerkundungsmethoden, physikalische und geophysikalische Untersuchungen angewandt und davon wurden relevante Ergebnisse prasentiert. Diese Ergebnisse wurden in das regionale geologische Inventar des Äspögebietes integriert, um die Entwicklung eines umfassenden Modells fuer den Gesteinskörper zu ermoglichen. Diese Modellvorstellungen sollen im Rahmen eines Validierungsversuches verwendet werden.

1. INTRODUCTION

The ZEDEX (Zone of Excavation Disturbance EXperiment) project was undertaken at the Äspö Hard Rock Laboratory (HRL) Sweden by ANDRA, United Kingdom Nirex Limited (Nirex) and SKB to enhance the understanding of the properties and mechanical behaviour of the Excavation Disturbed Zone (EDZ) surrounding a drift with respect to its origin, character, magnitude of property change, extent and their dependence on excavation method. Supporting studies to increase understanding of the hydraulic significance of the EDZ and to test equipment and methodologies for quantifying the EDZ were also performed. The rationale for undertaking this project is that the properties of the disturbed zone are considered to be of potential importance to the performance and safety assessment of radioactive waste repositories as the disturbed zone may provide preferential pathways to radionuclide transport and may affect the efficiency and effectiveness of plugs placed to seal underground openings. Previous documented work has shown that the excavation of a tunnel will cause disturbance to the rock mass surrounding the tunnel. The character and magnitude of the disturbance is a function of the tunnel, the method of excavation used to excavate the tunnel and the properties and nature of the rock mass and how these relate to the presence of the air filled void. The hypothesis tested was that the nearfield (<2m) disturbance should be reduced by the application of an appropriate excavation method (smooth blasting or tunnel boring). The hypothesis also predicted that the far-field disturbance (>2m) would essentially be independent of the excavation method. The ZEDEX project comprised investigations before, during and after excavation of the drifts and allowed a comparison to be made between the Excavation Disturbed Zone caused by two different excavation techniques. The site for the study was located at the beginning of the TBM drift at a depth of 420m below ground.

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