| The upper Yangtze River waterway is mostly mountainous rivers with more distribution of obstructive reefs and shoals.As the economic and shipping development increases the requirements for the maintenance scale of the waterway,the waterway needs to be improved by blasting reefs to achieve the safe navigability of the waterway.However,blasting will have a serious impact on the ecological environment of the project waters,and the shock wave generated by it will have a significant effect on the damage of four fish.Therefore,it is of great theoretical value and practical significance to carry out research on the transmission law of underwater blasting shock waves,to clarify the damage effect of shock waves on fish and the critical safety pressure of four fish,and to propose a safety protection plan for four fish under the action of shock waves.At present,there is no systematic and complete research results on the damage and protection of the four fish by the shock wave transmission law of underwater blasting and shock wave pressure in inland waterways.In view of this,this paper is based on the combination of field monitoring experiments and numerical simulation calculations,to carry out research on the transmission law of underwater blasting shock waves and the influencing factors,to reveal the degree of damage and characteristics of the four major fish,to clarify the safety critical pressure value of shock waves that the four major fish can withstand,and to propose ecological protection schemes and arguments applicable to actual projects.The main work and conclusions are as follows.(1)Relying on five underwater blasting and reef-clearing projects,including Zhuan Zaozi underwater blasting and reef-clearing project,Xuan Tanmiao reef-clearing project,Three Gorges drainage box culvert underwater blasting and excavation project,Huang Cao Gorge reef-clearing project,and Chongqing Guoyuan Port major cargo terminal project berth harbor pond excavation project,field monitoring experiments on the peak pressure of underwater blasting shock waves were conducted to carry out research on the transmission law of peak pressure of shock waves.In this study,40 underwater drilling and blasting shock wave field monitoring experiments were conducted,and 80 sets of underwater drilling and blasting shock wave peak pressure data were obtained for different source distances(8～400 m),explosive amounts(6～234 kg),number of holes(1～12)and water depths(6.2～22.0 m).The results showed that the peak pressure of underwater blasting shock wave was extremely high,which could reach more than 10~6Pa;the pressure of underwater drilling blasting shock wave was instantaneous and completed within 20 ms from generation to completion.The theoretical formula of shock wave pressure attenuation with time and the empirical formula of peak pressure of shock wave in water were obtained by fitting the monitoring data.The fitting coefficient R~2 was0.87 and 0.85,respectively,indicating that the fitting formula could accurately reflect the transmission law of peak pressure of shock wave with distance and dosage.(2)On the basis of field monitoring,the equation of state of the reef,blocking material,explosives,water body and air,etc.is considered,and the peak pressure transmission law of shock wave in underwater borehole and its influencing factors are studied by numerical simulation,and the results show that the blast shock wave diffuses to the surrounding water body in a spherical form with the blast center as the origin;the shock wave is reflected when it reaches the water surface and produces obvious weakening effect.The results of the analysis of the factors affecting the shock wave transmission law show that compared with single-hole blasting,double-hole,three-hole and four-hole blasting can attenuate the shock wave pressure by 10%～50%,50%～60%and 60%～80%,respectively,indicating that the peak shock wave pressure is smaller with a certain amount of explosives and a larger number of holes;the peak shock wave pressure at a blasting water depth of 5m is on average 37.3%and 50.3%lower than that at a blasting water depth of 16m.The average decrease of 37.3%,50.5%,60.1%and 68.5%for blasting water depth of 5m compared with that for blasting water depth of 16m indicates that the smaller the blasting water depth is,the faster the decay of peak shock wave pressure;the effect of flow velocity on shock wave transmission can be ignored.(3)Based on the damage observation experiment of four large fish under the action of shock wave pressure of underwater blasting,the damage characteristics and safety critical pressure of four large fish were determined.The results showed that the herring and grass carp of 10-15cm were basically dead under the action of shock wave peak pressure of 7.06×10~5 Pa.The silver carp and bighead carp of 10-15cm died 50%under the shock wave peak pressure of 7.06×10~5 Pa.The juvenile silver carp of 15～30cm was seriously damaged under the peak pressure of 20.00×10~5 Pa blast wave,and the mortality rate was more than 60%.The main organs damaged by underwater blast shock waves were brain nerves,swim bladder and liver,and the other organs were gall bladder,spleen,intestine,body cavity,eyes,etc.The damage level decreases with the increase of fish length;the pressure tolerance of silver carp and bighead carp is slightly stronger than that of cyprinid and grass carp;the safety critical pressure of juvenile fish from 5 to 30 cm is about 0.14×10~5 Pa,and that of adult fish above 30 cm is about 0.75×10~5 Pa.(4)Through the analysis of the mechanism of action,it is clarified that the underwater millisecond differential blasting technology can improve the blasting effect,increase the construction efficiency and control the initial peak pressure of blasting shock wave;through the comparison of the field monitoring experimental results,it is clear that the bubble curtain technology can generally reduce the shock wave in the transmission process by more than 90%;through the fish safety critical pressure,the empirical formula of shock wave transmission law and the location of fish near each beach hazard The results show that the engineering design of the blasting and reefing area of Fo Mian Beach meets the ecological safety requirements of the four major fish species;the blasting areas of Tou Wai Liang,Dadu Kou,Daliang,Cai Seed Liang and He Shang Beach should be designed with bubble curtain to ensure that the fish in the vicinity are not damaged by the blasting shock waves;In the reef clearance area by Tiger beam blasting,the underwater micro-difference borehole blasting and bubble curtain technology should be adopted simultaneously to ensure that the nearby fish are not damaged by the blasting shock wave. |
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