Conventional borehole pressure relief can meet the requirements for preventing rock bursts, but it can also easily destroy the roadway, resulting in system support failure. Taking coal-like samples with boreholes as the research object, the pressure relief effects of the same-diameter boreholes and variable-diameter boreholes are compared and analyzed by a uniaxial compression test. The joint pressure relief mechanism of the variable-diameter drilling hole is discussed. The experimental results show that the stress–strain curve of variable-diameter drilling sample occurred the phenomenon of pre-peak stress drop and post-peak stress plateau, which indicates that the variable-diameter drilling hole can enhance the plastic characteristics of coal-like samples. The borehole size dramatically influences the variation of various pressure relief indexes. The evolution law of AE counting the pre-peak and post-peak of borehole samples verified the abovementioned law. Variable-diameter drilling can enhance the plasticity of samples, weaken the brittleness and reduce the impact tendency. Under the maximum size of the variable-diameter drilling hole and the same-diameter drilling hole is same, the pressure relief effect is more significant. The results obtained in this paper can provide a new theoretical basis and technical guidance for borehole pressure relief and roadway support.

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