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RESONANT COLUMN AND BENDER ELEMENT TESTS OF UNSATURATED CORAL SAND ON XISHA ISLANDS IN SOUTH CHINA SEA
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摘要: 为了确定珊瑚砂的动剪切模量和阻尼比等分析岛礁场地稳定性的主要动力学参数，本文针对我国南海西沙群岛某岛礁珊瑚砂，利用共振柱-弯曲元系统，研究了围压、相对密实度及饱和度对该珊瑚砂动剪切模量和阻尼比的影响规律。研究发现：(1)在饱和状态下，该珊瑚砂样的最大动剪切模量(G0)与围压及相对密实度整体呈现正相关关系，并且随着围压的增高G0对相对密实度的敏感性逐渐降低；(2)在非饱和情况下，该珊瑚砂样的动剪切模量比的整体范围略高于饱和状态下的动剪切模量比，而其阻尼比略低于饱和状态下的阻尼比；(3)该珊瑚砂样出现最小阻尼比和最大G0的饱和度约为10%；(4)在同样的围压下，珊瑚砂的特殊结构导致建立在硅质砂相对密实度和孔隙比的G0经验预测公式在预测珊瑚砂G0时分别出现了偏高和偏低的情况，本文根据珊瑚砂G0随围压的变化规律，对珊瑚砂G0经验预测公式进行了修正。研究成果可为南海西沙岛礁珊瑚砂场地稳定性分析中动力学参数取值提供参考。Abstract: Determining the dynamic shear modulus and damping ratio of coral sand is prerequisite for analysing the stability of islands under dynamic loadings. Therefore,this paper presents a study on how the confining pressure,relative compactness and saturation affect the dynamic shear modulus and damping ratio of the coral sand in South China Sea. It uses the resonant column and bender element tests. The results show the follows. (1)The maximum dynamic shear modulus G0 of saturated coral sand sample is positively correlated to the confining pressure and the relative compactness,and are decreases sensitively to the relative compactness with the increase of the confining pressure. (2)The dynamic shear modulus ratios of the unsaturated coral sand are slightly higher than those of the saturated samples,while its damping ratios are slightly lower than those of the saturated samples. (3)The coral sand samples show the maximum G0 and the minimum damping ratio at the saturation of about 10%. (4)The predicted G0 by the empirical functions based on the relative compactness and the void ratio of siliceous sand are higher and lower respectively than the results obtained in the tests. Thus,the empirical formula of G0 as a function of confining pressure is modified according to the tests. This study contributes sample values of the dynamic shear modulus and damping ratio for the stability analysis of coral sand sites on the reef islands in South China Sea.
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图 1 共振柱-弯曲元试验系统示意图
Figure 1. Illustration of the resonant column apparatus with bender element system
图 2 珊瑚砂原样的粒径分布曲线
Figure 2. Grain size distribution curve of the original coral sand samples
图 3 不同围压下珊瑚砂G0与相对密实度的关系(a)及其趋势线斜率与围压的关系(b)
Figure 3. Variations of G0 along with the relative compactness at different confining pressure(a) and the variation of the slope of its trend line with the confining pressure(b)
图 4 不同相对密实度下珊瑚砂G0与围压的关系(a)及其趋势线斜率与相对密实度的关系(b)
Figure 4. Relationship between G0 of the coral sand sample and the confining pressure at different relative compactness (a) and the variation of the slope of its trend line with the relative compactness(b)
图 5 不同围压和相对密实度下珊瑚砂动剪切模量(a~c)及其归一化曲线(d)
Figure 5. Dynamic shear modulus of coral sand(a~c) and its normalized curve (d) under different confining pressure and relative compactness
图 6 不同围压和相对密实度下珊瑚砂阻尼比
Figure 6. Damping ratio of coral sand under different confining pressure and relative compactness
图 7 珊瑚砂最大动剪切模量G0随饱和度的变化(a)及不同饱和度下动剪切模量G随动剪应变的变化(b)
Figure 7. The variation of the maximum dynamic shear modulus G0 with saturation degree (a) and the dynamic shear modulus G as a function of dynamic shear strain under various saturation degree(b)
图 8 不同饱和度下动剪切模量比(a)及阻尼比(b)
Figure 8. Normalized dynamic shear modulus curve(a) and damping ratio(b) under different saturation degree
图 11 不同围压下A1和A2修正值
Figure 11. Revised value of A1 and A2 under different confining pressures
图 12 本文考虑围压和相对密实度的G0预测值和试验值对比
Figure 12. Comparison of the G0 values obtained in the lab tests and the prediction considering the confining pressure and relative compactness
表 1 珊瑚砂样基本物理性质指标
Table 1. The physical properties of the coral sand samples in this study
颗粒比重 最大干密度/g·cm-3 最小干密度/g·cm-3 最大孔隙比 最小孔隙比 2.75 1.41 1.11 1.48 0.94 
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表 2 本文试验方案设计
Table 2. Experimental design in this study
围压σ/kPa 相对密实度Dr/% 饱和度Sr/% 测试内容 共振柱(RCA) 弯曲元(BES) 50 55、65、75 100 G-γ、λ-γ G0 100 55、65、75 100 150 55、65、75 100 200 55、65、75 100 150 75 0 150 75 10 150 75 20 150 75 30 150 75 40 150 75 50 150 75 60
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