Study On Harmful Effect Of Shock Wave In Underwater Borehole Blasting Nearby Bridge Pier And Its Protection Methods

With the implementation of the development strategy of the Yangtze River Economic Belt and the new requirements of navigation standards,the underwater reef blasting project presents a trend of large volume and large dose.At the same time,with the advancement of urbanization in China,the regional environment is becoming more and more complex and the control of the harmful effects of underwater shock waves is also more stringent.Although the related theories of land blasting have been well rounded,in the underwater environment,the existence of the water has led to great differences between underwater bored blasting and land blasting.Due to the large number of influencing factors in the shock wave propagation process,the difficulty in monitoring the shock waves,and the relatively few engineering practices in underwater bored blasting,the development of the theory of shock wave in underwater bored blasting and the study of related laws have been limited to a certain extent,and it has caused great difficulties to predict the harmful effects of underwater shock waves in practical projects.In view of this,based on the dredging project of the Jiulongpo-Chaotianmen section of the Yangtze River Channel,a numerical calculation model for underwater bored blasting that matches the actual reef blasting project was constructed.Based on the study of the propagation law of shock wave in underwater bored blasting,a comprehensive analysis of the influence of the harmful effects of underwater shock waves on piers was conducted,and then the question of which setting modes of bubble curtain can effectively reduce the harmful effects of underwater shock waves was systematically studied.The main research methods and results include the following aspects:(1)A detailed investigation on the dredging project of the Jiulongpo-Chaotianmen section of the Yangtze River Channel was conducted,including analyzing engineering situation of study area,geological conditions and blasting construction plans,which lays the foundation for the follow-up numerical simulation research.(2)By using the explicit dynamic analysis finite element software,the numerical analysis model of bench blasting in accordance with the actual project was constructed.Moreover,the propagation and attenuation laws of shock waves in water are obtained,the shock wave rises to the peak in a very short time,then decays exponentially to the hydrostatic pressure,and finally fluctuates above and below the hydrostatic pressure value.At the same time,comparing the peak pressure data of shock waves obtained in tests,the reliability of the numerical calculation model was verified,which laid the foundation for the following research.(3)Considering that the dynamic response of bridge piers during underwater bored blasting is the result of the combined effect of seismic waves and shock waves,multiple seismic isolation trenches are set in the numerical calculation model to reduce the seismic effects.Furth more,the harmful effects of shock waves on the piers are obtained,the maximum stress and velocity response of bridge piers are located in the middle of piers and the toe of piers.Therefore,in practical projects,the two parts of piers should be focused on.(4)In order to study the influence degree and regularity of multiple parameters in setting modes of bubble curtains on the reduction of shock waves,based on the orthogonal test and range analysis method,an orthogonal numerical calculation scheme considering the influencing factors of the number of bubble curtains,bubble curtain spacing,and bubble curtain protection distance was constructed.The results of orthogonal test and sensitivity analysis show that the bubble curtain can be set by following the principle of more objects and more closer to the protected object,which can effectively reduce the harmful effects of shock waves on buildings.