Influence Of Bench Blasting On Roadway Stability Under The Condition Of Combined Mining

Under combined mining conditions, influence domains of the two kinds mining method overlap each other, a mining effect influences or disturbances another equilibrium system, the two kinds of excavation system induce or restrict each other, so as to form a composite dynamic change system. Because of the special arrangement relationships between the underground and the open pit mine, resulting in the roadway stability problems under open-air and underground composite mining more complicated. The stress in the surrounding rocks of roadway designed under open pit slope is composed of bench blasting in open pit and underground mining, which influence each other. Under this stress filed, the surrounding rocks will always stay in the process of stress redistribution, which makes the rock strength weakening gradually. In addition, open-pit mining will reduce the surrounding rock vertical stress, unloading stress produced by mining makes the stability of roadway surrounding rock becomes very sensitive, leading to the influence of underground mining on the roadway stability more significant than ordinary and the instability probability of surrounding rock increases. Although the use of combined mining has achieved very good performance, but the production process also encountered challenges. In Anjialing Open-pit mining process, with the help of a large number of bench blasting excavation, blasting seismic wave will apply a dynamic load on the roadway surrounding rock, which may causes surrounding rock slip failure. Under multiple step blasting, stress in roadway surrounding rock always keep in a dynamic redistribution. Based on Anjialing Open-pit mining, using the existing blasting wave theory, roadway stability under blasting vibration was researched, the influence of blasting vibration on roadway stability was explored. Through the numerical simulation, the effects of seismic wave to the roadway surrounding rock loose circle, the stress and displacement of lining and anchor was researched, finally, theoretical calculation of actual collected data validates the analysis and find out the rule of the influence of blasting vibration on existing roadway under combined mining. The main conclusions are as follows: 1.Roadway surrounding rock failure is mainly caused by BVAE(accumulation effect of blasting vibration). The failure mechanism can be explained using burst and storage characteristics of BVAE.2.The association degree of blasting vibration at the interval τ was quantified and the relationship between the association degree and its effects on the surrounding rock damage was shown, which reveal the key of surrounding rock instability induced by blasting load.3.The weakening function of BVAE to the physical and mechanical properties of surrounding rock was analyzed using wavelet packet frequency energy band analysis, and the characteristics of main frequency of blasting vibration signals trend to lower frequency is found.4. The removal of rock mass makes the stress in surrounding rock release, which makes the maximum tensile stress increase and its change amplitude has a great relationship with the stripping rock mass weight and its relative position.5. The reason, mechanism and results of blasting vibration cumulative effect is revealed.Correlation function Rz shows the association degree of blasting vibration at interval r, revealing the causes of blasting vibration cumulative effect; Wavelet analysis shows the characteristics of blasting vibration to be low in multi band multi modal, revealing the interaction process of blasting vibration cumulative effect and its performance characteristics; Verify the damage development of surrounding rock caused by blasting vibration using PFC, which revealing the effect results of blasting vibration cumulative effect.6.The BVAE on the stability of roadway can not be ignored, so more attention should be paid in the blasting.