Numerical experiments modeling different three-dimensional mine lay out were performed, using two boundary condition sets defined by presence or absence of horizontal additional stress. The determined stress/deformation states were used afterwards for quantitative characterization of the effect of horizontal tectonic stress on system behavior. Local rock mass load intensity and the related failure possibility were assessed using the indicators called safety margins related to several well known failure criterions such as: the maximum principal stress', Coulomb-Mohr's, and true triaxial strength theories. The safety margins' spatial distribution served then as a basic measure helpful in identifyng areas of higher failure risk. The analysis permitted selecting the safest mining layout of the three considered, and recommend it for the practical development in one of the Polish underground copper mine.
A problem of interaction between room-and-pillar panel, exploited in so called roof deflection technology, with overburden strata subjected to high level stress has been recognized as one of the most important geomechanical and safety issues in the Polish deep copper mines. In 1997 and 2005, measurements of three dimensional Stress field were carried out at three locations in the KGHM's copper mines in Polkowice (Fig. 1), Poland (Katulski et al., 1997, Fabich and Pytel, 2005). The results obtained were similar to other stress measurements performed throughout the world and they have proved that at the depth of 1100m below the surface, the average horizontal stress value within the hard dolomite deposit is greater of about 50 pct. than the vertical stress value estimated to be equal to 29.7MPa. Despite of a limited number of such measurements, their results could be used as a basis for a practical extensive design comparative study utylizing the very refined FEM quantitative computations.