In this paper the method of failure nuclei delineation in a rock masses is presented. This method is implemented in a software program for strong seismic events forecasting. It is based on direct use of the fracture concentration criterion. The method is applied to the database of microseismic events of the North Ural Bauxite Mine. The results of this application, such as: efficiency, stability, possibility of forecasting rockburst are discussed.
In underground mining, a very important safety issue relates to strong dynamic events. It is necessary to develop effective forecasting techniques of their scale and location. The first stage of strong events forecasting is the delineation of dangerous volumes, then in these areas additional analyse should take place. The purpose of this paper is to develop the clusters delineation procedure using the kinetic concept of solids strength. This procedure should be as much as possible formalized and have a minimum of assigned parameters, for objectivity of the obtained results and possibility of its subsequent analysis.
For better detection of prognostic features before a strong event, the delineated areas should include the whole failure nucleus and should not contain irrelevant events, which do not correspond to strong event triggering. Any restrictions on the geometry (Sobolev et al. 1991) should not be imposed both at the delineation stage and at the correction stage, when additional (new) events are considered. According to development of the kinetic concept of strength (Zhurkov 1965) using the concentration criterion of fracture (Kuksenko et al. 1975) and the two stage model of fracture (Tomilin & Voinov 1993), the weak events (they have one scale level less than strong ones) must take part in the preparation of the strong ones, which are the result of exceeding the critical threshold concentration of weak events. Therefore, we have only two physical parameters, defining strong event preparation: the size (R) or energy class (K) of the seismic event to be for forecasted and the threshold concentration parameter CP - a dimensionless value which is the distance between centres of cracks (hypocenters of microseismic events) divided by their mean size. The area of failure nucleus was delineated on the basis of the calculation of the concentration parameter for each pair of microseismic events. Then the pairs with CP value lower than a given threshold, which have common events, were aggregated in clusters. Other researchers use only the parameter CP as an effective predictive parameter (Mansurov 200 1). All registered microseismic events shall be regarded as the development of new cracks in a rock masse, because we have no additional information for a more correct classification. An attempt to overcome the difficulties of the concentration parameter estimation leads to using two additional parameters. In the procedure of failure nucleus delineation only the last recorded events NEv will be used, since according to the recurrence interval plot a constant number of weak events (in average) corresponds to the preparation of each strong event.