The Controlled Balsting Technique For Excavation Of Small Interval Zone In Wulong Tunnel And Its Application

The construction of Wulong tunnel in freeway from Chongqing to Changsha is faced with cutting blasting engineering in small interval zone. The seismic action of blasting results in the part or whole collapsing of inter-space rock in all probability, which will influence the stability of surrounding rock. These not only affect the construct, but also add to the difficulties of protection construction. Thus, the engineering cost increases, even the safety accidents easily occur.In order to solve these problems resulting from cutting blasting in small interval zone of Wulong tunnel, the wave detecting of rock mass and the field experiments for seismic effect were carried out. The damage range of surrounding rock caused by the common blasting method in Wulong tunnel is analyzed by the measurement. The vibration characteristic of inter-space rock and its varying laws are studied. Based on them, the technical measures of driving blasting are put forward when the thickness of inter-space rock are 7～12m and 4～7m.It can be found from results of the observation and the wave detecting that the depth of rock overbreak exceeds 50cm and the damage range of surrounding rock reaches 1.3～2.3m by the common blasting method in Wulong tunnel. In small interval zone, the common blasting can't be used.A lot of measured results of blasting vibration, in which the thickness of inter-space rock of tunnel is 12m, show that the vibration velocities of the front tunnel wall close to the work 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 samller with the increase of distance which is less than 20m. The reasonable millisecond-delay time is not shorter than 50ms in blasting.In view of the situation that the seismic effect of driving blasting must be strictly controlled in small interval zone of Wulong tunnel, the excavating scheme is put forward. Furthermore, the blasting parameters and design charts are given according to the concrete conditions which the thickness of inter-space rock are 7~12m and 4~7m. The application of the technique of blasting proposed in the thesis to Wulong tunnel construction shows that the blasting scheme and the blasting parameters are reasonable. The overbreak...