ABSTRACT

The paper presents the results of endoscopic research in the fracture zone of rock layers in the premises of underground headings. The evaluation of roof rocks carried out using a visual camera allows for the determination of their quality as it is equally effective method to the other popular ways of describing rock quality. The results obtained allowed for the proper estimation of fracture zone around the underground heading In selected coal mines.

INTRODUCTION

Drifting a heading in a mine results in the appearance of the fracture zone in the rocks around the heading. It happens due to the undesirable increase of stresses and exceeding the strength of rocks. The range of the fracture zone has a massive influence on the selection of the type and parameters of a support for the given heading. The design works related to the proper selection of the supports for headings should be carried out On the basis of a thoroughly analysed rock mass, on the basis of a realistic picture of fracture and discontinuities as well as strength tests in natural conditions. The tests carried out using a borehole endoscope are the optimal way to determine the amount and range of fracture in the premises of a heading in a mine.

The knowledge of basic parameters relating to fracture, i.e. number of fractures, their distribution and the character of fracture, is applied in a series of geotechnical classifications for describing rock mass quality. As an example, one may quote here the classification based on the tunnelling quality index Q, where the following parameters were distinguished: number of fracture systems, roughness of fissure, weathering of fissure walls (Hoek et al. 1980, Pilecki 2002).

Parameters relating to fracture are also included in the geomechanical classification based on the RMR index (joint spacing, condition of discontinuities and discontinuities orientation) (Bieniawski 1976, Hoek & Brown 1980, Sheorey 1993).

Also the RQD index, commonly used in the evaluation of drill core quality, is based on the number of Overt fracture.

The authors of the paper made an attempt at the evaluation of rock mass quality for the analysed areas of several coal mines on the basis of endoscopic observations.

BSERVING FRACTURE ZONE

Observations of the range of fracture zones in headings were carried out using borehole endoscope. The device is applied to observe the walls of testing boreholes by means of infra-red camera and the picture is recorded on videotape. It gives a possibility to make a quick and easy quantitative as well as qualitative evaluation of fissure and fracture in rock mass (Majcherczyk & Malkowski 2002).

Such tests may be carried out in the testing boreholes distributed in random spots in the contour of the heading (Fig. 1). Due to gravitation and horizontal delamination of rock layers, the observations are most often carried out in the heading's roof, in vertical or inclined boreholes.

The ‘in situ’ endoscopic observation gives an opportunity for quantitative and qualitative evaluation of discontinuities of rocks around the heading.

This content is only available via PDF.
You can access this article if you purchase or spend a download.