Fatigue damage can occur in surface rock engineering due to various factors, including earthquakes, blasting, and impacts. The underlying cause for the variations in physical and mechanical properties of the rock resulting from impact loading is the alteration in the internal pore structure. To investigate the evolution characteristics of the pore structure under impact fatigue damage, red sandstone subjected to cyclic impact compression by split Hopkinson pressure bar (SHPB) was analyzed using nuclear magnetic resonance (NMR) technology. The parameters describing the evolution of pore structure were obtained and quantified using fractal methods. The development of the pore structure in rocks subjected to cyclic impact was quantitatively analyzed, and two fractal evolution models based on pore size and pore connectivity were constructed. The results indicate that with an increasing number of impact loading cycles, the porosity of the red sandstone gradually increases, the T₂ cutoff (T_2c) value decreases, the most probable gray value of magnetic resonance imaging (MRI) increases, the pores’ connectivity is enhanced, and the fractal dimension decreases gradually. Moreover, the pore distribution space tends to transition from three-dimensional to two-dimensional, suggesting the expansion of dominant pores into clusters, forming microfractures or even macroscopic fissures. The findings provide valuable insights into the impact fatigue characteristics of rocks from a microscopic perspective and contribute to the evaluation of time-varying stability and the assessment of progressive damage in rock engineering.

In recent years, the development of marine hydrocarbon resources has led to an increased demand for research on the marine soil bearing capacity and cyclic loading effect in marine engineering design. Because of the difficulties and high costs involved in obtaining high-quality soil samples from offshore sites, in situ testing techniques have become the preferred method of determining design parameters in offshore geotechnical engineering projects. This paper provides a review of the current state of marine penetrometer deployment technology used in offshore engineering investigations and presents a summary of the T-bar penetrometer test for measuring marine soft clay. The existing literature research on penetration mechanisms, numerical simulations, laboratory experiments, and field tests of the T-bar penetrometer in the field of marine geotechnical engineering are analyzed. Finally, the potential difficulties, challenges, and prospects of the T-bar penetrometer tests are discussed.