Model Experimental Study And Application Of Deep-hole Blasting In Hard Rock For Mine Shaft

The drilling and blasting method is mainly used in the construction of mine shaft. Shaft lining and surrounding rock is subjected to negative impact because of the blasting vibration effect caused by frequent and large-scale blasting operation while completing the rock excavation. Blasting energy should not only be fully used to improve advancing speed and efficiency, but also be effective controlled to keep the vibration of surrounding rock and supporting structures within the limits.In order to solve the problem in shaft excavation, combining with projects "Research on Efficient Blasting Technology for Hard Rock Section of Shaft and Roadway in Zhujixi Coal Mine" and "Research on Key Technology of Efficient Blasting and Rapid Excavation for Hard Rock Section of Deep Shaft in Hengyuan Coal Mine", model tests for shaft cut blasting in two-circle simultaneous blasting and three-circle delay blasting were carried out based on theoretical analysis of blasting seismic wave propagating properties. Blasting vibration and strain tests were also carried out. Moreover, field monitoring and analysis of blasting vibration were presented in engineering application to ensure the stability of surrounding rock and supporting structures. Main conclusions are as follows:(1) According to similarity theory, similarity criterion for coalmine shaft was established; model material, model geometry and blasting parameters were also determined. Blasting holes were reserved during concrete pouring. Two-circle model contains ten blasting holes and three-circle model contains twenty blasting holes to implement simultaneous blasting and delay blasting. The influence of blasting to longitudinal wave velocity was also analysised and the damage degree is determined by longitudinal wave velocity changing. It was found that simultaneous blasting can generate more energy resulting in greater cavity depth, stronger vibration effect, and larger blasting damage; while delay blasting can make full use of free surface leading to greater cavity volume and lower blasting damage.(2) Vibration monitoring was conducted in all cut blasting tests. The results showed that vibration in horizontal was the smallest, and vibration in longitudinal and vertical were bigger and almost the same. Simultaneous blasting could generate larger vibration velocity and more blasting energy, which is good for cut blasting leading to great cavity volume and depth. While millisecond delay blasting could generate smaller vibration velocity and better shape, which is good for auxiliary and surrounding holes blasting, reduces overbreak and underbreak. With the delay time increasing, waveforms were independent to each other, peak vibration velocity was determined by dosage in different relays. When the total dosage was certain, an effective method in reducing and controlling blasting vibration was increasing the relays of detonation and limiting the dosage in simultaneous detonation. By spectral analyses of blasting vibration signals, vibration signal on specimen surface had a wider frequency band and main vibration frequency.(3) Dynamic strain in all cut blasting tests,112measuring points, were analyzed and effective strain waves were obtained by conversion of voltage signal to strain signal. The change rule of strain-time curve was also analyzed.(4) Based on the results of model tests, a cutting mode of double-row with the same depth was put forward according to rock properties, blasting equipment performance and drilling equipment condition. The blasting parameter was optimization designed considering the arrangement, diameter and depth of blasting holes, the charge and firing sequence. In engineering application, advance rate and efficiency was improved, blasting hole utilization reached91.7%, the vibration of shaft wall and surrounding rock was reduced. This would provide guidance for rapid excavation and safe construction of coalmine shaft achieving good social and economic benefits.(5) Through field test and analysis of blasting vibration, the propagation attenuation formula of seismic wave and the energetic distribution of signals with different frequency bands were obtained. The peak particle velocity and time are related to the charge of each interval and delay time. Delay blasting method and controlling maximum instantaneous charge were adopted to reduce the blasting vibration and to improve blasting efficiency.