Haijian Su

The study of fiber‐reinforced coral aggregate seawater shotcrete (FRCASS) is essential for island and reef infrastructure development and maintenance. However, its behavior under simultaneous environmental degradation and dynamic loading is not well understood. In this study, a multi‐scale investigation combining nanoindentation, dynamic compression tests, and mesoscopic numerical simulation was conducted to evaluate the micromechanical properties, dynamic response, and degradation mechanisms of polypropylene fiber and steel fiber reinforced coral aggregate seawater shotcrete subjected to dry‐wet cycling. Nanoindentation tests quantitatively identified the coral aggregate as the weakest microphase (with elastic moduli primarily in the 0.3–1.0 GPa range), governing the distinctive “trans‐aggregate” cracking mode. Dynamic tests with a Split Hopkinson Pressure Bar showed that polypropylene fiber‐reinforced concrete (PFRC) consistently achieved a dynamic strength growth rate of about 12.5% under impact pressures of 0.2 to 0.4 MPa, while steel fiber‐reinforced concrete (SFRC) experienced a significant decrease in strength enhancement from 17.31% to 2.03%. After 30 dry‐wet cycles, SFRC suffered severe mechanical degradation, with fiber residual stress plummeting by 93.75% (from 400 to 25 MPa), while PFRC demonstrated superior durability, showing only a 68.4% reduction (from 380 to 120 MPa) and minimal mass loss due to the chemical inertness of polypropylene and salt crystallization clogging pores. A high‐fidelity 3D mesoscopic finite element model calibrated with nanoindentation‐derived parameters was developed using LS‐DYNA, which accurately replicated the macroscopic dynamic stress–strain response, cracking patterns and fiber effect. The results underscore the effectiveness of polypropylene fibers in enhancing damage resistance and durability of FRCASS under marine environmental conditions, providing critical insights for the design of sustainable marine infrastructure.

The fracture behavior of concrete structures under dynamic loading exhibits rate-dependent (RD) characteristics. To study the dynamic fracture (DF) mechanisms of two-dimensional (2D) concrete structures, this study proposes a DF analysis method with a novel integration of the finite particle method (FPM) and a RD cohesive zone model (CZM), which enables effective analysis of mesoscale DF in concrete. Specifically, a traction-separation law is presented, wherein only the traction strength is RD. The changes in traction with the loading rate for CZM are derived. Subsequently, the equations of motion of particles are detailed, and the internal forces of the cohesive element (CE) are developed to characterize the RD CZM. Afterward, a CE solver is implemented within the explicit FPM analysis framework. Then, a benchmark study on a single element is conducted to verify the traction-separation law of CZM. A standard DF benchmark is examined to validate the effectiveness of the proposed method. It is found that the offered approach effectively captures the path of crack propagation and the delaying characteristics of microcrack development. Applying the mesoscale fracture model of concrete structures, the intricate DF behavior of concrete is analyzed, providing enhanced understanding of crack expansion and load-bearing capacity.

Anchored surrounding rock is prone to large nonlinear deformation and instability failure under dynamic disturbances. The fissures and defects within the surrounding rock make the rock mass’s bearing characteristics and deformation instability behavior increasingly complex. To investigate the effect of the fissure angle on the dynamic mechanical response of the anchored body, a dynamic loading model of the anchored, fissured surrounding rock unit body was established based on the finite difference–discrete element coupling method. The main conclusions are as follows: Compared to the indoor test results, this numerical model can accurately simulate the dynamic response characteristics of the unit body. As the fissure angle increased, the dynamic strength, failure strain, and dynamic elastic modulus of the specimen generally decreased and then increased, with a critical angle at approximately 45°. Compared to 0°, when the fissure angle was 45°, the dynamic strength, failure strain, and dynamic elastic modulus decreased by 17.08%, 15.48%, and 9.11%, respectively. Additionally, the evolution process of cracks and fragments shows that the larger the fissure angle, the more likely cracks are to develop along the initial fissure direction, which then triggers the formation of tensile cracks in other regions. Increasing the fissure angle causes the specimen to rupture earlier, making the main rupture plane more directional.

In actual underground rock engineering, to prevent the deformation and damage of the rock mass, rock bolt reinforcement technology is commonly employed to maintain the stability of the surrounding rock. Therefore, studying the anchoring and crack-stopping effect of rock bolts on fractured granite rock mass is essential. It can provide significant reference and support for the design of underground engineering, engineering safety assessment, the theory of rock mechanics, and resource development. In this study, indoor experiments are combined with numerical simulations to explore the impact of fracture dip angles on the mechanical behavior of unanchored and anchored granite samples from both macroscopic and microscopic perspectives. It also investigates the evolution of the anchoring and crack-stopping effect of rock bolts on granite containing fractures with different dip angles. The results show that the load-displacement trends, displacement fields, and debris fields from indoor experiments and numerical simulations are highly similar. Additionally, it was discovered that, in comparison to the unanchored samples, the anchored samples with fractures at various angles all exhibited a higher degree of tensile failure rather than shear failure that propagates diagonally across the samples from the regions around the fracture tips. This finding verifies the effectiveness of the numerical model parameter calibration. At the same time, it was observed that the internal force chain value level in the anchored samples is higher than in the unanchored samples, indicating that the anchored samples possess greater load-bearing capacity. Furthermore, as the angle α_s increases, the reinforcing and crack-stopping effects of the rock bolts become increasingly less pronounced.