ABSTRACT:

The variations of damage factor from blasting for driving a dritt in soft rock are studied by means of damage theory. The distinguishing deformation features of the surrounding rock of a drill are analyzed. The effective supporting structure and its building method for drifts in soft rock are put forward.

I.
INTRODUCTION

Supporting a drift in soft rock is a complicated technological problem facing the extraction or underground coal. For a long time, much research is carried out by Chinese and foreign scholars, and many important achievements are reached, but some defects still exist in the research(He, 1999,wang Liu& 2000). Blasting for driving a drift in soil rock damages its surrounding rock, and results in low strength and stability of the rock, which is not taken into account in the research. Soft rock is the sort of that which is soil, weak, loose in its basic characteristics. In engineering, the soft rock displays low strength, many small openings, cracks, and joints, large plastic deformation before breakage by load, et al. Relatively, soft rock has low modulus of elasticity and large Poisson's ratio. Up to now, there has not been the consensus of the definition of soft rock yet, more than ten various definitions are still existing(He.1999) In engineering practice, blasting drives most of the mine drifts. Although the various blasting methods, such as smooth blasting, controlled directional split perimeter rock blasting et al (Wang,1990, Yu,1997,Dai,2000), are used helpful to protecting the surrounding rock, damage from blasting for driving happens inevitably in the surrounding rock. The damage results in the change in mechanic properties of rock, especially in soft rock. In order to support effectively the drill in soft rock, it is helpful very much to study the law that blasting for driving damages the surrounding rock, analyze the law that the damaged rock deforms, and find out the reasonable supporting structure and building method.

2.
SURROUNDING ROCK DAMAGE FROM BLASTING FOR DRIVING

The smashed, the cracked, and the damaged areas are usually formed after charge in rock is shotted. For driving a drift, the perimeter shotholes are placed near to its contour with other holes are far from the contour. Under this condition, it is supposed that damage in the surrounding rock damage is resulted from the explosion in the perimeter holes. When smooth blasting is used, the explosion in perimeter holes makes the through crack between them, breaks the rock between the perimeter holes and production holes, and else damages the surrounding rock. This damage affects greatly the deformation the drift and the stability of its supporting.

3.
DISPLACEMENT AT THE DRIFT WALL AFTER THE ROCK DAMAGED

The damage in the surrounding rock by perimeter blasting is a non-uniform and anisotropy. If the deformation and the stability of the damaged rock are supposed to be plane strain problem, according to the reference (Yu.1993), the effective stress in damaged rock. From it, it is known that the radius of plastic area in the rock.

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