Study On The Technique Of Driving Blasting For Ren Hechang Tunnel In Yuhuai Railway

As a main construction method, the technique of driving blasting for tunnel is widely used in shallow tunnel engineering. The blasting scheme and its parameters not only directly concern with the blasting quality, the efficiency and benefit of the tunnel construction, but also affect the stability of the surrounding rock, the effect of tunnel support as well as the safety of the buildings around the tunnel.Taking Ren Hechang shallow tunnel in Yuhuai railway passing through the residence buildings with 11 floors and the Cloverleaf Junction as a background, the field blasting experiments of seismic effects have been done. Base on the measurement of the vibration velocity of particles on the ground and the surrounding rock of the tunnel, the propagating characteristic of seismic waves of driving blasting is studied. The attenuation coefficient and exponent of seismic waves on the ground are obtained by statistical analyses, which are K = 232.8 and a = 1.89. The further analysis and calculation shows that when the tunnel passes through the buildings and the Cloverleaf Junction, only the maximum charges of per period are restricted within 9Kg and 20Kg respectively, the vibration velocity can be satisfied with the control standard.Comparing the varying trend of the vibration velocity of the ground in front of the free face with that in back of the free face, it is found that the vibration velocity on the ground in back of the free face is larger than that in front. That is, the tunnel has an amplifying effect for the ground vibration caused by driving blasting and the amplification coefficient reaches at 1.5. In addition, the distance between the free face and the second-lining is no less than 17 ~ 40m, thus, the tunnel liner could be out of the impact of blasting vibration.In view of the situation that the seismic effect of driving blasting must be strictly controlled in Ren Hechang construction, the excavating scheme is put forward that the tunneling blasting with short footage in upside section and the horizontal-hole bench blasting with long footage...