Abstract

The goal of research was to determine the spatial distribution of the fractures and to recognize the electric properties of the rock mass around the mining openings in the O/ZG "Polkowice – Sieroszowice" underground copper mine (the Lower Silesian region, Poland). The measurements were carried out with the multielectrode resistivity ABEM Lund Imaging system and georadar equipment produced by MALA Geoscience.

The measurements were conducted on the side walls of the two selected mining openings, i.e. inclined drift A5F and dip road D2. On each side wall 3 measurement profiles of the 40m length were designed. The profiles were located in the lower, middle and upper parts of the side walls.

Applying inverse combined algorithm the resistivity changes were recognized to the depth of approx. 8m from the side walls. The results of resistivity imaging have indicated the occurrence of the increasing resistivity zones in the vicinity of the side walls. They can be related to the fractured and loose zones of the rock mass. The obtained resistivity values change in the range from approx. 15Ωm to over 100Ωm. It has also been observed that the depth of the fractured zones changes and depends on the side walls height. In the both openings the fractured zones extensions increased up to 6–7m of depth near the roofs and were the lowest near the floors, reaching 2–3 m. The deeper, not disturbed zones of the rock mass showed the resistivity below 10Ωm.

The GPR reflection measurements with the use of 500MHz and 250MHz antennas delivered information about fractured zones distribution to the depth of 5.0m and 10.0 m, respectively. The results of measurements obtained for the both antennas were similar, therefore in the paper only recordings for 250MHz antenna are presented. The results of GPR surveys were correlated to the depth of about 8m with the results obtained for the resistivity method. The majority of fractures has been located by the GPR method near the openings' roofs in this way confirmed the results from the resistivity method.

1 Introduction

The aim of the geophysical research was analysis of ability of resistivity imaging (RI) and georadar reflection technique (GPR) application for detection of natural fractured zones surrounding openings and fractures induced by mining activity. Due to the fact that the GPR and RI methods base on different physical fields, therefore in the interpretation only some regions with anomalies may be correlated for both methods and so-called quantitative interpretation may be carried out.

The georadar and the resistivity imaging surveys were carried out in two galleries chosen by the O/ZG "Polkowice-Sieroszowice" copper mine (belonging to the KGHM Polska Miedź S.A. mining company), i.e. in the inclined drift A5F, region SR-14 (Fig. 1a) and in the dip road D2, region Jm-21 (Fig. 1b).

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