Field investigations on rock fragmentation under deep water through fractal theory

•The systematic in-situ experiment of rock breaking under deep water is studied.•To satisfy the needs of environmental protection and channel navigation, rock breaking/drilling technology is applied.•To determine the optimal combination, a series of in-situ field investigations are carried out.•Height of rock hammer and position distance have a great influence on rock fragmentation. Though orthogonal test, the optimal combination of parameters is determined.•The distribution of fractal dimension for each factor can be satisfactorily described by normal distribution. Rock breaking/drilling technology instead of blasting is used in excavation of channel navigation. Rock hammer is a useful tool to achieve the objectives, which is more environmental-friendly than conventional blasting method. Fractal theory is appropriate easily to study rock fragmentation characteristic. To determine the optimal combination of parameters based on fractal theory, a series of in-situ field investigations are carried out. The results show that the height of rock hammer and position distance have a great influence on rock fragmentation. The optimal combination of parameters is determined to be height 27 m, row spacing 3.5 m, position distance 1.7 m, and impact frequency 2 times. The distribution of fractal dimension for each factor can be described by normal distribution. An exponential function can be used to obtain satisfactory regression relationship between nonuniformity Cu and the fractal dimension D, while a linear function is more appropriate for the relationships between the correction coefficients Ku and Kc and the fractal dimension D.