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During underground hard-rock mining, the drilling and blasting method currently remains the most economical excavation method, and the rock may experience a multistrain-rate spectrum under quasi-static, dynamic, and rheological loading conditions and their combination as well. The study on the damage mechanism of rock under multistrain-rate condition that induced by mining excavation is the fundamental issue for predicting the mining-induced hazards such as rockburst. In this study, the state of the art of rock damage and failure under different strain rates is reviewed first. Then, the numerical model for rock failure under multiple strain rates is formulated when the rock damage is taken as the main thread. Meanwhile, we summarize our work in this area over the past ten years, and the constitutive law for the damage and failure of rock under multistrain rates is presented. Finally, several numerical examples, i.e., rock damage and failure under combined static and dynamic load, rock damage and failure triggered by dynamic stress redistribution due to excavation, rock damage and failure induced by blasting, and rock damage and failure due to the combination of dynamic disturbance and rheological load, are presented. Based on these numerical simulations, the associated rock damage mechanism and failure behaviors under differently combined multiple strain rates are clarified, which may provide a theoretical basis for clarifying the rock failure mechanism during rockbursts and rock blasting. Also, further studies on the damage and failure of rock under multiple strain rates are suggested.

The coal seam methane poses a serious threat to production equipments and personal safety in underground coal mining of China. Loosening blasting is one of the most important measures to enhance gas drainage in coal seam and to prevent gas outbursts. In this work, a coupled multiphysical model for the blasting damage of coal and gas flow in coal seam is proposed, based on which the evolution of damaged zone and release of stress concentration in coal seam before and after blasting near the working face is examined by means of numerical simulation according to an actual in situ condition during underground coal mining. The numerical simulation indicates that, after the loosening blasting in coal seam, a broken zone with radius of 1.0 m and a loosening zone with radius of 1.2m are formed around the blasting hole. Moreover, due to the loosening blasting, the stress concentration area above blasting hole is extended from � = 3~4 m to � = 7~10 m deep into the coal seam, while that above the controlling hole is extended from � = 3~4 m to � = 4~8, thus confirming that the loosening blasting has notable effects on increasing coal bed permeability and enhancing gas pre-drainage. Keywords: Coalbed, loosening blasting, gas drainage, numerical modelling

Understanding and cognition on characteristics of acoustic emission (AE) signals is the foundation and precondition of read comprehensively AE signals. Traditional Fourier amplitude spectrum and power spectral density(PSD) representations based on Fourier transform have limitations, that is, it loses any information related to time and is unable to completely reflect the non-stationary characteristics of AE signals essentially. In this paper, based on wavelet transform, the relationship between wavelet coefficient in every frequency bands and power spectral density is derived; PSD estimate method and time-dependent PSD estimate method based on wavelet transform are also presented in this paper. The feasibility of the presented method is illustrated by AE Signal of rock processing and analysis.