| Traditionalmode of transportation by sea has been unable to meet the needs of economic interchange,complementation and improvement in coastal areas,so the construction of subsea tunnels is an imperative.Though the project of subsea tunnels brings benefits to human beings,the high frequency bandwidth and high energy shock pulse generated by blasting operation may lead to different degrees of impact on marine organisms,such as behavioral effects and death.Studying the shock pulse generated by blasting construction of subsea tunnels in water,predicting the intensity of shock pulse and evaluating the noise fields are of great significance to marine ecological environment and marine life protection.The mine tunneling method or drilling blasting,is required in the construction of subsea tunnels.The stress wave generated by the subsea tunnels blasting changes in form with theattenuation of energy.It propagates in the form of shock wave,compressive stress wave and seismic wave in the seabed strata successively.When the wave reaches the bottom interface,it refracts into water and forms the shock pulse.In this thesis,the shock pulse generated by subsea tunnel blasting has monitored in real time and related numerical were analyzed.The main contents and results of this paper are as follows:1.According to the needs of real-time monitoring of shock pulse generated by subsea tunnel construction projects surrounding Xiamen in water and the signal energy,a monitoring system including hydrophone,signal conditioning module,signal acquisition and recording module and signal display module is designed.2.The time-frequency analysis of the shock pulse is carried outby MATLAB software,and the parameters of peak sound pressure level,root mean square sound pressure level,sound exposure level of the monitoring data are calculated.The main conclusions are drawn in the following:when the total charge is 150.0kg and the maximum charge of a single section is 41.0kg in the subsea tunnel drilling blasting,the peak pressure value of shock pulse in water can be as high as 6.4kPa;from the view of power spectral density,the intensity of the shock pulse is mainly distributed in low frequency,and decreases with the increase of frequency;when the shock pulse in water measured at the same horizontal distance but different depths has similar waveforms,the amplitudes are quite different;shock pulse energy in water monitored at the same depth but different distances,will rapidly attenuate as the distance increases.3.The improved Hilbert-Huang transform(HHT)method based on noise assisted analysis has been used to analyze the time-frequency-energy of the shock pulse.The algorithm uses ensemble empirical mode decomposition(EEMD)when performing modal decomposition.When the white noise with uniform distribution is added to the time-frequency space of the original signal,the mode effectively overcomes the modal aliasing problem of empirical mode decomposition(EMD)in the traditional HHT algorithm.For it makes the analysis signal continuous on different scales.Through the transformation,it can be found that the energy of the analyzed signal is mainly concentrated in the range of 0-300Hz,and the continuous high amplitude is mainly concentrated in the time 0.4-1.0s and the normalized frequency of 0.07-0.28.These details can be further utilized to analyze the impact of shock wave in water on fish and marine mammals in the construction sea area.4.In this thesis,Cole’s peak pressure fitting formula is used to fit the data obtained by monitoring,it is found that the fitting results deviates greatly from the measured data,and the correlation index is R2=0.22.Then the new peak pressure fitting formula Pm=e-3.91·((?)/R)-1.65·(HS/R2)5.55 based on the method of dimensional analysis is obtained.In addition to the explosive charge Q and distance from explosion point to measuring pointdistance R,two new parameters are added in the new formula:the vertical distance H from the explosive position to the seabed interface and the horizontal distance S from the explosive position to the measuring position.The results show that the correlation index is R2=0.98,and the average fitting error between the predicted value and the measured value is 13.9%,which means that agood fitting effect is achieved.Therefore,the final results provide an effective method for the prediction of the peak pressure of the shock pulse generated by subsea tunnel blasting in water. |
