The Experimental Investigation On Seismic Effect Of Shallow Tunnels

The technique of driving blasting is used as a main constructive way in shallow tunnels in rocky zone. By this way, blasting seismic effect is inevitable. The control of blasting seismic effect is concerned with not only the blasting quality, the tunnel constructive efficiency and the benefit of the tunnel construction, but also the stability of the surrounding rock, the effect of tunnel timbering and the safety of buildings around the tunnel. In order to control the blasting seismic effect effectively, the blasting seismic waves' characters should be studied.In view of the Ren Hechang shallow tunnel in Yuhuai railway, which will dig under two high buildings, the field experiments on seismic effect have been done. By measuring vibration velocities of particles in the ground and the surrounding rock of the tunnel, the blasting seismic waves' characters have been studied. By analysing the change character of the vibration velocities of the front and the back per face, it is found that the vibration velocities at the ground of the back pre face are larger than those of the front. That is, at the ground of the back pre face, there is the magnification effect of the vibration velocities, the magnification coefficient is no less than 1.3. Analysing and comparing the vibration velocities at the different regions of the digging surface changed, there is also the magnification effect of the vibration velocities in these regions.The field experiments have been done on seismic effect of the building. By studying the change character of the blasting seismic waves' along the vertical direction of the building, it is found that the vertical vibration velocities are larger 1.2-4 times than the horizontal vibration velocities at the same floor. The vertical vibration frequency is much closer to the self-frequency of the building than the horizontal vibration frequency at the same floor. Along the vertical direction of the building, the blasting seismic waves' frequency becomes closer to the self-frequency. As a result,the vibration velocities have the trend to increase.In order to calculate the particle vibration velocity in drilling blasting accurately, the corresponding formula has been brought forward. Compared with the results of the Sodev's empirical formula, the results of the formula are much closer to the values of the actual vibration velocities. 80% of the results of the formula are better than those of the Sodev's empirical formula.