Study On Viberation Effects Of Ground Resulted From Blasting In Shallow Tunnel

With the development of China's traffic, a great deal of shallow tunnel in downtown area will be constructed, in which some shallow tunnels need to be excavated by blasting because of engineering and environment conditions. The vibration effects produced by blasting will endanger the safety of buildings close to tunnel. As a result, it is an urgent problem that how to forecast the vibration effects and control it so as to ensure the safety of building in engineering.Taking the project of Ren Hechang shallow tunnel in Yuhuai railway as the background, the field experiments of the vibration effects of the ground in tunnel blasting have been done. Base on the measurement of the waveforms of the vibration velocity in different distances away from the blasting sources on the ground, the vibration characteristic of the ground and its varying laws are studied. The results of the tests and analyses show that there are many differences in the vibration effects resulted from different blast-holes blasting. The vibration effects of cutting hole blasting is the most intensive in all kinds of blast-hole and its vibration intensity is over two times greater than that of the other blast-holes blasting. The vibration velocities of the ground resulted from relief; breast and trim holes blasting do not always become greater with the increase of their single period charges. The dug region of the shallow tunnel may cause the hollow effect of ground vibration in tunnel blasting, that is, the vibration velocity of ground in back of the free face is larger than that in front. The tunnel has an amplifying effect for the ground vibration caused by blasting and the value of amplification coefficient is 1.3-2.3. The blasting vibration effects along the tunneling direction can be forecasted by Sadov's formula, but the formula is not suited to the forecast of the opposite direction.In the light of the measurement of vibration effects of ground resulted from blasting in Ren Hechang tunnel, the numerical simulation of ground vibration is studied by using dynamic finite element method. The loading methods, calculating models, calculating conditions and calculating methods are studied. It is available to study problem which the vibration load is forced upon the excavating boundary of tunnel in simulating blasting vibration effects. So the high nonlinear problems of basting needn't to solve. Comparing the calculated values of different inputted dynamic waves, it is found that the forms of inputted dynamic wave can affect the characteristics of the vibration wave obtained by simulating. The simulated wave of ground vibration, obtained by using the vibration wave of excavating boundary as the inputted load of numerical calculation, resembles the measured wave in shape and the attenuation of vibration velocity with time and distance accords with the measured results. Its peak vibration velocity and main frequency can be used in...