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AbstractThe construction of an island airport on a coral reef will inevitably encounter wave, tidal and aircraft takeoff and landing loads. To study the dynamic response of the coral sand island airport under these loads, a 1:50 laboratory model test was conducted with Meiji Reef Airport as the engineering background. The model test studied the pore water pressure characteristics of the coral sand strata beneath the airport runway under wave loads with different wave heights, tidal loads with different tidal heights, and aircraft impact loads with different cyclic loading times. Additionally, the displacement characteristics of the coral sand strata beneath the airport runway under the aircraft impact loads with different cyclic loading times were also studied. The results show that the pore water pressure of coral sand strata under the airport runway decreases with the increasing offshore distance under the wave and tidal loads. The change of wave height has little influence on the pore water pressure of coral sand strata, while the change of tidal water level has a significant effect on it. As the number of aircraft impact load cycles increases, the cumulative excess pore pressure in the coral sand strata under the airport runway no longer increases and plastic deformation occurs. The research can provide a reference for the runway foundation treatment of the island airport under construction and planning. [ABSTRACT FROM AUTHOR]

Adjacent cyclic explosions significantly impact the stability of underground anchored caverns. Based on the similar model test of the vault explosion of the anchored cavern, the dynamic analysis finite element software ANSYS/LSDYNA(18.0) was used to establish a model of the straight wall side explosion of the underground anchored cavern and conduct a numerical simulation. When the total amount of explosion load is the same, we compared the stress time history curve, displacement time history curve, tunnel wall displacement, and circumferential strain curve of the surrounding rock in the underground anchored cavern (under both a high-level single-side blast and a low-level cyclic side blast). We obtained the dynamic response rules of the surrounding rock. By comparing the damage evolution process of the surrounding rock in the two situations, the damage accumulation law of the surrounding rock was analyzed. At the same time, the axial stress distribution characteristics of underground anchor cavern anchors under the action of cyclic explosion were studied. The findings demonstrate that when the total level of blast load adjacent to the cavern is the same, the displacement and circumferential peak strain of surrounding rock and the axial stress of rock bolt in the high-level single explosion are greater than those in the low-level cyclic explosion. However, compared to a single explosion, the rock mass suffers more damage in the cyclic explosion. This study will provide engineers with information that will assist them with a better understanding of the cumulative damage mechanisms of surrounding rock, as well as the stress characteristics of rock bolts under dynamic loads near the explosion site, which will be used to design underground caves with anti-blast features. [ABSTRACT FROM AUTHOR]

The temporal and spatial effects of a complicated excavation process are vital for an ultra-shallow buried large-span double-arch tunnel excavated under an expressway in service. Numerical simulations are urgent and necessary to understand the effect of the total construction process. Taking Xiamen Haicang tunnel as a research object, the total excavation process of three pilot tunnels and the three-bench reserved core soil method of an ultra-shallow buried large-span double-arch tunnel with a fault fracture zone under an expressway was simulated using software FLAC3D. The deformation of the surface, surrounding rock, underground pipelines, tunnel support structure and partition wall of the three pilot tunnels and the main tunnel was analyzed, and the dangerous areas and time nodes were obtained. When the tunnel was excavated to the fault fracture zone, the deformation of the surface and surrounding rock increased significantly. The rock and soil within 20 m behind the excavation surface of the pilot tunnel were greatly disturbed by the excavation. During the excavation of the main tunnel, the horizontal displacement of the middle partition wall moved slightly towards the main tunnel excavated first. The research results can provide a reference for the construction design of double-arch tunnels. [ABSTRACT FROM AUTHOR]