The advanced borings are used in many countries to prevent the gas outburst in the coal mines and their effects are widely proved. But the site experiments are not so easy, for they require a lot of time and funds.
The author made a model experimental study to investigate the effect of the advanced borings on the stress relief. A three-dimensional model experimental apparatus of about 1: 80 geometrical scale was used. The boring diameter, the number of borings, the spacing of borings and the strength of model coal seam were selected as the parameters of the experiments. As the model rock mass, the gypsum plate was used and as the model coal seam, artificial seam composed of the mixture of water, gypsum and diatomite. The scale of the stress and the strength was 1: 40.
The effect of the stress relief was measured by the degree of stress relief defined by the author. The relationship between this degree and the above mentioned experimental parameteres are reported. The strength of the coal seam and the boring diameter are the most important parameters which determine the effect of stress relief.