SUMMARY:

The influence of blasting on the remaining rock has been a subject for research during several years at the Swedish Detonic Research Foundation. As a result of this a model has been established which predicts the extent of the zone of damage in the remaining rock for various charge concentrations per meter borehole and various blastin? situations. Since the shear strength of unfavourably oriented planes of weakness has a major influence on the rock mass stability, research was initiated to investigate the shear strength of joints after movements in the joints have occurred. These investigations were made in laboratory scale with a specially designed direct shear apparatus which allows movements to be created in existing and potential joints before the shearing of the joints takes place. Surface profile measurements on the used geological structures were also performed. The shear tests were carried out at low normal loads corresponding to the vertical stresses in an open pit bench.

ZUSAMMENFASSUNG:

Die Einwirkung der Snrengung auf ''das umgebende Gestein ist seit mehreren Jahren ein Forschungsgegenstand der Stiftung der Schwedischen Detonikforschung. Als Resultat dieser Forschung ist ein Modell festgelegt worden woraus sich die Ausbreitung der Beschadigung des rueckstandigen Gesteines bei Verwendung verschiedener Ladungskonzentrationen per Meter Bohrloch und bei verschiedener Sprengungsverhaltnissen im voraus feststellen Lasst, Da die Scherfestigkeit unguenstig orientierter Schwacheflachen auf die Stabilitat des Gebirges entscheidend einwirkt, ist die Forschungsarbeit auf die Feststellung der scherfestigkeit der kluefte nach Bewegung derselben eingerichtet worden.

Diese Untersuchungen wurden im Laboratoriummasstab mit einem fuer direkte Scherversuche speziellen Apparat durchgefuehrt, der das Zustandebringen von Bewegungen in pre-existierenden und potenziellen klueften zulasst, ehe der Scherversuch durchgefuehrt wird. Man hat auch die Profilen der Kluftflachen gemessen. Die Scherversuche geschiehen bei Belastungen, die den Normalspannungen in einem Tagebauabsatz entsprechen.

RESUME:

L''influence du sautage sur le rocher environnant a ete un objet de recherche pendant plusieurs annees de la Fondation Suedoise de la Recherche Detonique. Le resultat de cette recherche fut l''etablissement d''un modele permettant de predire l''etendue de la zone d''endommagement du rocher environnant par rapport à l''emploie de concentrations de charge Variees par metre de trou de mine et aux conditions de sautage differantes.

Comme la resistance au cisaillement des zones d''affaissement d''une orientation defavorable exerce une influence decisive sur la stabilite de la roche le but des travaux de recherche fut d''etudier la resistance au cisaillement des joints ayant ete exposes aux mouvements.

Ces etudes furent effectuees en echelle de laboratoire à l''aide d''un appareil de con- Struction spàciale pour faire des essais de cisailiemerit direct et permettant de susciter des mouvements dans les joints preexistants et.rotentiels avant 1 ''execution de l''essai. Aussi a-t-on ensuite me sure les profils des surfaces des plans de fracture. Les essais de cisaillement furent effectues sous l''effet de contraintes moderees correspondant aux contraintes verticales dans un gradin d''exploitation à ciel ouvert.

INTRODUCTION

The influence of blasting on the remaining rock has been a subject for research during several years at the Swedish Detonic Research Foundation (SveDeFo). The aim of the work is to study deformations in the remaining rock caused by the blasting and to investigate effects on the strength of the rock.

The main part of the field investigations have so far been made at bench blasting operations in open pit mines in Sweden, the practical application being the possibility of increasing the final slope angle of a pit by using cautious blasting methods.

Since this problem particularly demands knowledge of the shear strength of blast damaged weakness planes in the rock shear strength investigations were initiated.

In this paper results from measurements of blast-induced rock mass deformations are presented. Models for prediction of the extent of the damaged zone at bench and tunnel blasting are described. Finally results from experimental investigations of the effects of simulated blast damages on the shear strength of rock joints are presented.

MEASUREMENTS OF BLAST-INDUCED ROCK MASS ''DEFORMATIONS AND PREDICTION OF THE EXTENT OF DAMAGE

Measurements of deformations in the rock mass behind open pit blasts have been performed using steel bars anchored in holes at different depths below the surface.

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