The distribution of discontinuities in the deep stratigraphic rock mass is random and irregular, and the spatial distribution has statistical self-similarity, which can be analyzed by fractal theory. The borehole wall image obtained based on the ultrasonic borehole imaging technology can clearly reflect the rich structural surface information such as the inclination, density, and crack width of the structural surface in the rock mass. Due to its inherent fractal characteristics, the fractal box dimension of the hole wall image can be used to describe the complexity of the structural surface. In the study, the fractal box dimension of the hole wall image and the RQD value of the rock mass are compared, and it is found that there is a linear correlation between the two. Therefore, the rock quality can be evaluated according to the fractal box dimension value of the hole wall image. Finally, a rapid quantitative evaluation method for rock mass quality classification is established based on ultrasonic borehole imaging technology and fractal method.

In situ stress field in deep strata is dominated by self-weight stress and tectonic stress, which is the dynamic source of a series of mining dynamic disasters such as rock burst, mine earthquake, and collapse. To develop deep resources and build deep engineering construction, the distribution characteristics of the in situ stress field must first be ascertained, so as to provide a basic basis for the engineering surrounding rock support design and disaster risk prevention and control. In this paper, taking the Sanshandao Gold Mine in the coastal area as the engineering background, in the early stage of the construction of the 2000 m deep shaft, the anelastic strain recovery method was used to measure the deep in situ stress field. The laws and characteristics of hysteretic elastic recovery of rock at different depths are obtained through experiments, and the effects of temperature, time, and other factors on strain recovery are revealed. The in situ stress test results are basically consistent with the traditional test methods. This method has low operational complexity and better application effect in deep formations. The research has accumulated test experience and basis for carrying out in situ stress measurement in the range of 2000 m and even deeper.

With the development of tunnels and other engineering constructions into the deep strata, rock masses are more prone to dynamic damage such as rock bursts under in situ conditions and excavation disturbances. The pore water in the rock mass will produce pressure changes during this process. According to the relationship between the change of pore water pressure and the development of rock mass damage, the variation rule and precursor characteristics of pore water pressure in the process of rock mass failure can be found. In this paper, through mechanical analysis, the evolution law of pore water pressure during the failure process of saturated rock is obtained. The study found that, in the process of rock failure, the pore water pressure presents three stages of linear growth, transition, and decrease. The rise and fall of pore water pressure are closely related to rock damage and influence each other. Through the observation of pore water pressure during coal mining, it is found that the coseismic effect of pore water pressure is significant. It is proved that there is a close correlation between the evolution of the stress field in the surrounding area of the stope and the change of pore water pressure in the surrounding area under the effect of mining disturbance. During the engineering practice, dynamic monitoring can be carried out on the change of pore water pressure inside the rock mass according to the law, and the precursor information of rock mass instability and failure can be explored.