珊瑚钙质砂是一种主要成分为碳酸钙的特殊岩土介质，广泛应用于岛礁建设中的军事与民用建筑。然而，目前关于石膏胶结钙质砂的力学性能及其微观机制的研究仍然匮乏。采用无侧限抗压强度试验探讨石膏胶结钙质砂试样的力学性能变化，通过电镜扫描技术分析了试样微观形貌的演化规律，揭示出石膏胶结钙质砂力学性能变化的微观机制。试验结果表明：在相同水灰比条件下，随石膏掺入比的增加，胶结钙质砂试样的无侧限抗压强度逐渐递增；在相同石膏掺入比条件下，低掺入比（5%和10%）试样的无侧限抗压强度随水灰比的递增而增大，而高掺入比（15%、20%和25%）试样的无侧限抗压强度随水灰比的递增呈现先增大后减小的变化趋势；石膏胶结钙质砂试样存在最佳配比：掺入比为25%、水灰比为0.9。上述力学性能变化的本质原因在于：建筑石膏（主要成分为半水石膏）遇水后发生化学反应，转变为二水石膏，连接了试样内的钙质砂颗粒，使土体颗粒间的胶结作用增强。

Coral calcareous sand, a unique geotechnical material primarily composed of calcium carbonate, is widely utilized in military and civil construction on island reefs. However, research on the mechanical properties and micro-mechanisms of gypsum cemented calcareous sand remains insufficient. The unconfined compressive strength test was used to investigate the changes of mechanical property of gypsum cemented calcareous sand samples. By scanning electron microscope test, the evolution laws of the sample's micromorphology was analyzed, and the microscopic mechanism of mechanical property of gypsum cemented calcareous sand was revealed. The results show that under the same water-gypsum ratio, the unconfined compressive strength of gypsum cemented calcareous sand samples increases with the gypsum content. Under the same gypsum content, the water-cement ratio of the samples with low gypsum content (5% and 10%) increases with the increase of water-cement ratio, and the water-cement ratio of the samples with high gypsum content (15%, 20% and 25%) increased first and then decreased with the increase of water-cement ratio. The optimum ratio of gypsum cemented calcareous sand samples is gypsum content being 25% and water-cement ratio being 0.9. The fundamental reason for the above changes in mechanical property is that building gypsum (the main component is semi-hydrated gypsum) reacts with water and transforms into dehydrated gypsum, which connects the calcareous sand particles in the samples and enhances the cementation between the soil particles.