In order to study the mechanical properties of submarine weathered granite under marine geological conditions, uniaxial compression tests were carried out on the original medium weathered granite of the seafloor of an offshore area in Pingtan, Fujian Province by using triaxial experimental apparatus to analyze the fracture characteristics, stress–strain characteristics, and compressive strength indexes. Based on the theory of discontinuous medium, the uniaxial compression and uniaxial tensile tests of rocks were simulated, and the microscopic mechanical parameters of discrete elements of granite samples were determined based on the indoor macroscopic mechanical tests: effective modulus E_t, compressive elastic modulus E_c, macro Poisson’s ratio μ, and uniaxial compressive strength σ_c. The results show that the parallel bond model has good simulation results for the uniaxial compression test, but the tensile strength and tensile–compression ratio were quite different from the experimental values. When the confining pressure is large, the calibrated parameter adaptability by uniaxial compression is poor. The reason for certain errors is a large resistance of the parallel bond model to particle rotation and the influence of normal stress on shear strength is not considered. The cementation model can be modified by adding coefficients based on laboratory test results.

Rock-socketed pile is one of the important foundation forms for offshore wind turbines, however, the construction of rock-socketed piles is very difficult. In this work, we propose to use hydraulic fracturing to pre-crack the rock foundation seabed around the piles to assist the construction of rock-socketed piles. Understanding the propagation mechanism of hydraulic fractures is the theoretical basis for hydraulic fracturing of rock seabed. Using mortar specimens containing single internal cracks and corresponding numerical simulations, hydraulic fracturing tests were carried out to study the influences of pre-existing crack characteristics and in situ stress on hydraulic fracture propagation behavior. The mortar specimens showed a tensile-shear failure mode under confining stress in hydraulic fracturing tests, and a macro-fracture penetrated the upper and lower ends of the specimens. Quantitative analysis of hydraulic fracture propagation behavior shows that under the comprehensive influences of the pre-existing crack angle and the stress, it is relatively easy to obtain good engineering results by selecting the pre-existing crack dip angle of 45°∼60° for directional hydraulic fracturing, and the increase of in-situ stress will improve the stability and deflection capacity of the cracks in the seabed.