Abstract
In tunnel blasting excavation, it is important to clarify the attenuation law of blast wave propagation and predict the blast vibration velocity effectively to ensure safe tunnel construction and protection design. The effects of the free surface area its quantity on the blast vibration velocity are considered, and free surface parameters are introduced to improve the existing blast vibration velocity prediction formula. Based on the Tianhuan railway Daqianshiling tunnel project, field blast vibration monitoring tests are performed to determine changes in the peak blasting vibration velocity based on the blast distance and free surface area. LS-DYNA is used to establish tunnel blasting excavation models under three operating conditions; subsequently, the attenuation law of blast vibration velocity and changes in the vibration response spectrum are analysed. Results show that the free surface area and number of free surfaces enable the blast vibration velocity to be predicted under various operating conditions: a smaller free surface area results in a narrower frequency band range, whereas more free surfaces result in a narrower frequency band range. The improved blast vibration velocity prediction formula is validated using field and numerical test data. It is indicated that the improved formula is applicable to various tunnelling conditions.
Highlights
In tunnel blasting excavation, it is important to clarify the attenuation law of blast wave propagation and predict the blast vibration velocity effectively to ensure safe tunnel construction and protection design
The free surface parameters were introduced into the vibration velocity calculation formula to improve the peak vibration velocity prediction formula based on the Sadoff formula and the peak vibration decay formula by Lu et al This is because the larger the free surface area, the greater is the number of free surfaces, and the smaller is the surrounding blast v ibration[22]
The numerical test fitting indexes indicate that the blast vibration velocity prediction formula considering the free surface parameters significantly improved the fitting indexes and yielded a better fitting effect than the base formula
Summary
Blast vibration hazard effects are evaluated by predicting the peak particle vibration velocity, and blast vibration control measures are formulated; the prediction accuracy is a longstanding issue in the blasting industry. The formula above does not reflect the effects of explosive properties, explosive type, charging method, hole size, and surrounding rock parameters on the blast vibration velocity. The larger the free surface area and the greater the number of free surfaces, the more prominent is the blasting effect. The prediction accuracy can be improved by investigating the effects of free surface factors on the blast vibration velocity and the influence law of the free surface into the prediction formula. The free surface parameters were introduced into the vibration velocity calculation formula to improve the peak vibration velocity prediction formula based on the Sadoff formula and the peak vibration decay formula by Lu et al This is because the larger the free surface area, the greater is the number of free surfaces, and the smaller is the surrounding blast v ibration[22]. The remaining variables are the same as those in Eqs. (1) and (2)
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