ABSTRACT

ABSTRACT:

We performed more than 700 hydraulic fracturing stress measurements in 140 test boreholes in various parts of Korea during the past 7 years. In this paper, the overall characteristics of the initial rock stress state in Korea are studied. For depths less than 310 m, the stress ratio (K) had a tendency to decrease and stabilize with depth. However, for some areas, excessive horizontal stresses with stress ratios greater than 3.0 were observed. A highly predominant orientation of the maximum horizontal stress component was not apparent but azimuths in the range of 70° to 90° (N70°E-EW) were superior in frequency. The results from the investigation of excessive horizontal stresses showed that there existed several regions where the localized excessive horizontal stress was large enough to potentially induce brittle failures around openings at depths of less than 300 m depth. Finally, results from a case study are briefly introduced in this paper.

1 INTRODUCTION

Rock stress measurement and its estimation has been regarded as one of the major branches of study in the geo-science fields including rock mechanics, structural geology, civil engineering, mining engineering, etc. Especially for civil and mining engineering problems, the initial rock stress state is one of the key factors required to evaluate the stability and failure around an excavated underground opening, and its importance increases as constructions go deeper and the scale of rock structures become larger. The stress induced failure around an opening does not directly mean the overall collapse of the rock structure but it may bring a temporary stoppage of excavation work and/or redesigning of the supporting system. In the long run, the stress induced problem can act as a serious obstacle to ensure the stability and the economical efficiency of underground construction procedures, especially for civil engineering sites.

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