Vibration Safety in Excavating a Multi-arch Tunnel by Blasting

摘要

Using the Dongkoutang Tunnel Project of the Shaoyang-Huaihua Expressway in Hunan Province as example, the author conducted scene experiments of the blasting vibration in the tunnel and studied the blasting vibration effect by using the software ANSYS/LS-DYNA. The Dongkoutang tunnel is a multi-arch tunnel with two holes and with two lanes in each hole. The mid-board between the two holes was 1.4m width and 5.1m height, which was constructed with concrete. The excavation sequence of the tunnel was first digging the mid-drift, secondly constructing the mid-board with concrete, and then excavating the two main holes by blasting. The numerical model combined with the blast excavation of the Dongkoutang tunnel was set up. The results of calculation showed that the Peak Particle Velocity (PPV) of vertical direction appeared more early than that of horizontal direction and the vibration wave in vertical direction attenuated more quickly in the mid-board. The PPV of horizontal direction was larger than that of vertical direction in the mid-board. Stress concentration emerged at the turning points of the cross section of the mid-board, especially at the top and the foot. The principal stress at the side of facing the blasting source was larger than that at the backside in the mid-board. The tensile stress did not occur in the mid-board and the peak value of compression stress was below 8Mpa, which was much smaller than the compressive strength of concrete. But during excavating the one main hole, blasting vibration would affect largely the arch crown and its nearby regions of another hole that had been dug. The blasting vibration effect on the stability of the surrounding rock and tunnel structure must be concerned.