Coral sand (CSD) was mixed with fine soil in varying proportions within real reef ground, exhibiting intricate dynamic behaviors under cyclic loadings, such as earthquakes. Undrained cyclic triaxial tests under diverse confining pressures and cyclic loading stress ratios (CLSR) with various fines content (FC) were conducted to systematically investigate the liquefaction characteristics and excess pore water pressure (EPWP) development. The coarse-grained CSD and fine-grained CSD displayed distinct failure modes, with the fine-grained CSD exhibiting a greater propensity for liquefaction. The liquefaction resistance of CRR₂₀ (cyclic resistance ratio) showed a trend of first decreasing and then increasing with the increase of FC, and reached the minimum value near the critical FC (FC_th). As FC and confining pressure increased, the axial deformation transformed from a gradual accumulation mode to a slow-rapid development mode. Particle breakage decreased with increase of FC but increased with confining pressure and CLSR. The plastic exhibited a trend of initial decrease followed by subsequent increase as FC rose, attaining its minimum value around FC_th. EPWP development curve changed from Type A to Type B as FC and confining pressure increased. EPWP exhibited differential responses during the third stage of Type B development pattern, when FC was relatively low (coarse-grained CSD), the growth rate of EPWP slowed down; while when FC was relatively high (fine-grained CSD), it continued increasing. The EPWP development of CSD mixtures exhibited notable discrepancy from that of quartz sand, thus a new unified EPWP model was proposed. The new findings obtained in this paper provided valuable insights for seismic design of infrastructure on coral island.

To investigate the propagation process of shock waves within a channel under different explosive yields and charge positions, this study established an experimental channel designed for individual soldier transit. Through experiments and simulations, it is found that the quantity and position of the charge affect the time history of overpressure and shock wave parameters. Within the tunnel, the propagation velocity and overpressure peak of the shock wave decreased with increasing of distance, while the duration and impulse of positive overpressure continuously extend and increase. When the charge equivalent increases, all shock wave parameters are enhanced, though the influence on the rate of overpressure peak attenuation is minimal. As the distance between the explosion center and the interior of the tunnel increases, all parameters decline. Both experiments and simulations reveal a unique change in the time history of overpressure and shock wave parameters near the 9 m measurement point inside the tunnel. By analyzing pressure contour maps and overpressure time history, it is discovered that wavefront movement is the primary cause. Based on the fundamental shock wave theory, a higher overpressure peak of shock wave results in faster wavefront motion. From the 3 m to 7 m section inside the entrance, the leading wavefront overpressure continuously attenuates with increasing distance, and its motion speed significantly decreases. However, the overpressure values of subsequent reflected waves attenuate more slowly or even exceed those of the leading wavefront due to continuous collision and superposition. Between the 7 m and 9 m sections inside the entrance, the reflected waves formed by later superposition catch up with and overlap the leading wavefront, resulting in an increase in the first peak value with increasing distance. This process is also clearly understood through the simulated overpressure contour map. Based on the experimental and numerical simulation results, a predictive model for shock wave overpressure within the channel, which has practical engineering reference significance, has been developed.