Attenuation of blast vibration in tunneling using a pre-cut discontinuity

• A sawing machine is applied on the tunnel face to generate a discontinuity.
• The effect of discontinuity is evaluated both experimentally and numerically.
• For this, the peak particle velocity before and after the discontinuity is compared with each other.
• A parametric study is performed to model the vibration propagation using MS & LP pattern.

A pre-cut discontinuity, similar to the pre-splitting around a tunnel periphery, is introduced to investigate the attenuation of the wave propagation due to tunnel blasting. For this, two empty holes were drilled to support the sawing jigs and a wire sawing machine with embedded industrial diamond wire was used to cut an artificial discontinuity near the initial blasting holes at the tunnel face. The peak particle velocity with/without pre-cut was measured during tunnel blasting and the effect of the pre-cut method was quantitatively accounted for, although, due to limited time and unfavorable field conditions, the cutting depth was not able to reach the initial design depth. Numerical analysis was also performed in order to model the tunnel geometry and blasting procedure. For this, a commercial package called UDEC was used and the accuracy of UDEC was initially proven by an analytical solution of the reflection and transmission of the incident wave. Various parametric studies including sequential detonations were performed and the reduction factor of attenuation with ideal cut-off discontinuity was shown to be 50%. Future work will concentrate on the improvement of the wire sawing machine to reduce the cutting time and three dimensional modeling of the blasting effect will also be performed.