Study On Vibration Effects Of Small Clear Distance Tunnel Driving Blasting And Its Application

The features of small clear distance tunnel are as following, its floor area is less than separated one,cost is less than multi-arch tunnel,shape is beautiful,but,it is difficult to construct,and need more technology.At the present time,the study on small clear distance tunnel is begin,research findings are in initial step,some of the problems are not reach to uniform,so there is theoretical and practical purpose in study finely and systematically on small clear distance tunnel.Taking the project of Wulong small clear distance tunnel driving blasting in Yu-chang high speed highway as the background in this thesis,the damage range of surrounding rock by the common blasting method is analyzed by the method of sound spotting to the tunnel surrounding rock and blasting vibration observation.The vibration characteristic of inter-space rock and its varying laws are studied. Inputting dynamic loadings,setting boundary conditions,choosing damping,such as these problems are discussed.By compare the field monitoring results with the calculation results to testify that use this calculation method to analyze vibration force is feasible. Based on them,check the safety of blasting method which is accepted in 7～12m and 4～7m clear distance by the way of numerical simulation, at the same time,the vibration effects of small clear distance tunnel driving blasting is studied.It can be found from results of the observation and the sound spotting that the depth of arch crown rock over-break exceeds 50cm and the damage range of surrounding rock reaches 1.3～2.3m by the common blasting method in Wulong tunnel.The reasons of over excavation is the improper layout of reinforced hole.The results of blasting vibration show that,in which the inter-space rock of tunnel is 12m,the vibration velocities of the front tunnel wall Close to the tunnel face of the back tunnel exceed 20cm/s.The vibration of inter-space rock resulted from blast seism have high main frequency and its main frequency usually exceeds 100Hz.The vibration velocities of the inter-space rock do not become smaller with the increase of distance which is less than 20m. The reasonable millisecond-delay time is not shorter than 50ms in blasting.The results of calculation show that,the error between calculation results and field monitoring is less than 20%,the calculation results are satisfied with the required precision of engineering calculation.The maximum vibration velocity that in 7～12m clear distance is 19.8cm/s caused by 2m footage full-face blast, and in 4～7m is 16.31cm/s caused by 1.3m footage full-face blast. The results are satisfied with the Safety Regulations for Blasting.By the condition of different blasting method and different clear distance,the law of blasting seismic wave is similarity; the maximum vibration velocity occurs on the abutment wall face to blasting over the range of 5～10m which is the longitudinal direction distance from blasting tunnel face.Surrounding rock faced to the blasting which longitudinal direction distance from blasting tunnel face is-5～15m is the most easy to broke,the rock on the back of blasting is safe.in the front of blasting area,the maximum vibration velocity become bigger along the direction of tunnel driving with the axial distance,than become smaller,it is become smaller inverse the direction of tunnel driving on the back of blasting area.