A New Method for the Prediction of Blast Vibrations and Suggestions with Respect to Uniform Reference Values for Short-Time Vibrations

摘要

This contribution presents an innovative, statistically supported method to predict blast vibrations in rock mass. For modelling the processes during and after detonation, a theory is employed which is based on linear momentum (so-called momentum theory), strongly supported by new measurement methods. During the course of the investigations, the following parameters have been found to dominantly influence vibrations: 1. charge WB, includes geometrical factors such as borehole length and diameter (kg) 2. detonation velocity c_d of the explosives used (m/s) 3. distance r between the points of emission and immission (m) and the statistically determined negative exponent n 4. factor R_M or R_S of the rock mass which is related to the specific blast momentum and the drilling and blasting technique used and is statistically determined together with the exponent m ( mm / kg or (mms/kgm)) The following regression formulas have been used: v_(max)=R_M(W_B·c_d·r~(-n))~m for measuremen ts of peak particle velocity v_(max)=R_S (W_B·c_d·r~(-n))~m for strain measuremen ts The vibration prediction presented here is based on extensive statistical data from many open pit mines. It turns out that the borehole charge per delay is not a key factor in the vibration magnitude. Employing the above regression formulae and using the concept of momentum theory, enables one to: 1. predict and reduce the level of vibrations with improved precision; 2. improve and adjust drilling, blasting and shotfiring techniques to the respective conditions; 3. increase the size of blast designs if the ignition is carried out according to the momentum theory, and 4. move quarrying areas and perform blast work closer to areas where vibration sensitive structures etc are located. In order to achieve a uniform basis for assessing the level of short-time vibrations the authors suggest new reference values on the basis of strain measurements as well as peak particle velocity. To this end, according to the building materials, structures will be classed into two groups. Strain as a directly assessable factor (in contrast to the alternative factor of peak particle velocity) depends on the conditions of the building ground of the respective structure. Ground conditions can be fixed either quantitatively by acoustic impedance or qualitatively by characterising the building ground geotechnically. The acoustic impedance can be correlated with the recorded frequency.