循环单剪下珊瑚钙质砂和普通硅质砂剪切特性对比研究

对普通硅质砂和西沙群岛珊瑚钙质砂开展多级正应力下循环单剪试验，对比多循环周期下两种砂土剪切性质和颗粒破碎的差异。研究发现，两种砂样在循环剪切下体积变化都比较微弱，剪切过程中存在阶段性剪胀，使得试样的轴向位移呈波动变化；循环单剪下剪应力峰值包络线可以用联合型指数函数表达；剪应力随循环周期变化分为同步阶段和差异阶段，两个阶段转变节点对应的循环周期数随着正应力的增大而迅速减小；同步增长阶段珊瑚钙质砂和普通硅质砂的剪应力变化一致，在差异阶段普通硅质砂的剪应力要高出珊瑚钙质砂。两种砂剪应力差异程度随试验正应力不同而变化，普通硅质砂剪应力最大可高出珊瑚钙质砂14.7%；珊瑚钙质砂和普通硅质砂的颗粒破碎存在明显差异，珊瑚钙质砂全粒径范围内颗粒破碎分布更均衡，普通硅质砂在特定粒径区间内出现了剧烈的颗粒破碎，颗粒级配曲线存在明显拐点。普通硅质砂和珊瑚钙质砂滞回曲线的形状及随循环次数的变化规律有显著差异，是两种砂样剪切性质不同的重要体现。

Comparative study of shear performance between coral sand and siliceous sand in cycles simple shear test

Cycles simple shear test are carried out for coral calcareous sand from Xisha Islands and local siliceous sand under multistage normal stress; and the difference of shear properties and particle breaking properties of two kinds of sandy soil under multiple cycles is compared. Under cyclic shear, both sand samples exist relatively weak volume changes and staggered shear dilatation which make the axial displacement curve of the specimen fluctuating. Shear stress peak envelope in cycles simple shear test can be expressed as an ExpAssoc function. Shear stress is divided into synchronous phase and differential phase with the change of cycle period; and the number of cycles corresponding to two phase transition nodes decreases rapidly as the normal stress increases. During the synchronous phase, the shear stress of coral sand and siliceous sand is consistent, while during the differential phase, the shear stress of siliceous sand is significantly higher than that of coral sand. The shear stress difference between the two types of sand varies with the normal stress, with the shear stress of the siliceous sand can be up to 14.7% higher than that of the coral sand in maximum. There are significant differences in the particle breakage between coral sand and siliceous sand. The distribution of particle breakage in the full particle size range of coral sand is more balanced. By contrast, siliceous sand has a violent particle breakage within a certain particle size range with obvious inflection points in the grading curve. The shape of the hysteresis loops and its variation with the number of cycles have significant differences between siliceous sand and coral sand, which reflecting the difference in the shear properties of the two sand samples.