INFLUENCE OF CORAL SAND PARTICLE SHAPE ON THE COM￣PRESSION PROPERTY OF COARSE GRAINED CALCAREOUS SOIL
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摘要: 珊瑚颗粒形状不规则是其显著区别于陆源土的一大特征。为揭示珊瑚颗粒形状对钙质粗粒土压缩性能的影响，人工挑选出不同形状(块状、枝状、棒状、片状)的珊瑚颗粒，以块状颗粒为基础，与其他3种不同形状的粗颗粒任意一种混合，控制不同颗粒形状配比制成钙质粗粒土试样，完成室内压缩试验，对比分析试验前后珊瑚颗粒的圆度、长宽比、扁平度和凹凸度等形状参数，评价颗粒形状对压缩性能的影响。结果表明：(1)粒径为10~20 mm钙质粗粒土的压缩模量是4~5.5MPa，回弹系数为42~53；(2)随枝状、棒状或片状颗粒掺量的增加(0、10%、20%、30%)，试样压缩模量呈小幅波状变化，回弹系数呈持续减小趋势；(3)各加载区间应力-应变曲线包括应力快速增长阶段、应力-应变同步增长阶段、应变增长阶段共3个阶段和1个稳定点；(4)随枝状颗粒掺量的增加，试样的长宽比和凹凸度逐渐增加，圆度和扁平度基本无变化；因颗粒破碎的影响，试验后试样的长宽比及扁平度有所增加，圆度及凹凸度则有所减小。选择钙质粗粒土地基时，应考虑其压缩性能，避免施工初期的快速加载。Abstract: The irregular shape of coral sand particles is a major feature that distinguishes it significantly from the ordinary terrigenous soil. In order to research the influence of coral sand particle shape on the compression property of coarse grained calcareous soil, different coral sand particles(block, branch, rod, flake) were selected manually. Based on the block particles, mixed with any of the other three different shapes of coral sand particles, the different particle shape ratios were controlled to make coarse grained calcareous soil samples, and the indoor compression tests were complete. The particle shape parameters such as roundness, length-width ratio, flatness and convexity of coral sand particles before and after the test were compared and analyzed. The effects of particle shape on the compressibility were evaluated. The test results show that:(1)The compression modulus of coarse grained calcareous soil with diameters of 10~20mm is from 4 to 5.5MPa, and the rebound coefficient is from 42 to 53; (2)With the increase of the amount of branch, rod or flake particles(0, 10%, 20%, 30%), the compressive modulus of the sample changed slightly, and the rebound coefficient continued to decrease. (3)The stress-strain curves of each loading range include one stable point and three sections which are rapid growth stress section, synchronous increase of stress and strain section, strain growth section; (4)With the increase of the amount of branch particles, the length-width ratio and the convexity of the sample increased gradually, while the roundness and flatness were unchanged substantially. Due to the influence of particle breakage, the length-width ratio and flatness of the sample increased after the test, while the roundness and concavity decreased. When selecting coarse grained calcareous soil foundation, its compressibility should be considered to avoid rapid loading at the beginning of construction.
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图 4 不规则颗粒尺寸参数图示
Figure 4. Graphical representation of dimension parameters of irregular particles
图 5 分选后颗粒形状的分布直方图
Figure 5. Distribution histogram of particle shapes after separation
图 6 不同棒状颗粒掺量的试样(S1~S4)e-lgP曲线
Figure 6. The e-lgP curves of samples(S1~S4)with different rod particle contents
图 7 不同掺量试样(S1~S10)压缩模量
Figure 7. Compression modulus of samples(S1~S10)with different mass ratio of particles
图 8 不同掺量试样(S1~S10)回弹系数
Figure 8. Rebound coefficients of samples in different dosage(S1~S10)
图 10 各加载阶段S1试样的应力-应变曲线
a. 0~50kPa的应力-应变；b. 50~100kPa的应力-应变；c. 100~200kPa的应力-应变；d. 200~400kPa的应力-应变；e. 400~800kPa的应力-应变
Figure 10. Stress-strain curves of sample S1(100%block) in each loading stage
图 11 S1、S5、S6和S7试样压缩前后长宽比与扁平度平均值
Figure 11. Average values of ratio of length to width and flatness before and after compression test for samples S1, S5, S6 and S7
图 12 S1试样(100%块状)压缩前后的长宽比与扁平度概率密度曲线
Figure 12. The probability density curves of aspect ratio and flatness of sample S1(100% block) before and after compression test
图 13 压缩前后的枝状颗粒和块状颗粒
a.压缩前的枝状颗粒；b.压缩后的枝状颗粒；c.压缩前的块状颗粒；d.压缩后的块状颗粒
Figure 13. Pictures of dendritic and block particles before and after compression test
图 14 S1、S5、S6和S7试样压缩前后圆度与凹凸度平均值
Figure 14. Average values of roundness and convexity before and after compression tests for samples S1, S5, S6 and S7
图 15 S1试样(100%块状)压缩前后的圆度与凹凸度概率密度曲线
Figure 15. The probability density curves of roundness and convexity of sample S1(100%block) before and after compression test
表 1 干燥钙质粗粒土试样的物理性质指标
Table 1. Physical indices of dry coarse grained calcareous soil
颗粒粒径/mm 比重 干密度/g·cm-3 初始孔隙比 10~20 2.78 0.87 2.195 
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表 2 4种形状颗粒组合试样的质量百分比
Table 2. The mass ratio of four shapes particles of the combined samples
S1 S2 S3 S4 S5 S6 S7 S8 S9 S10 块状/% 100 90 80 70 90 80 70 90 80 70 棒状/% 0 10 20 30 0 0 0 0 0 0 枝状/% 0 0 0 0 10 20 30 0 0 0 片状/% 0 0 0 0 0 0 0 10 20 30
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表 3 不规则颗粒尺寸参数
Table 3. Dimension parameters of irregular particles
符号 描述 面积 A 3D图像中面积的平均值 周长 P 3D图像中周长的平均值 Feret长度 FL 最大费雷特长 Feret宽度 FW 最大费雷特宽 Feret厚度 FT 最小费雷特宽 凸面积 CHA 3D图像中，通过填补后颗粒面积的平均值
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表 4 分选前颗粒形状参数的统计结果
Table 4. Statistical results of particle shape parameters before separation
圆度 长宽比 扁平度 凹凸度 平均值 0.425 1.629 1.782 0.070 标准差 0.118 0.461 0.798 0.041 变异系数 0.278 0.283 0.448 0.580 集合区间 0.423~0.428 1.619~1.638 1.765~1.799 0.069~0.071 集合区间长 0.005 0.019 0.034 0.002 偏态系数SK 0.003 2.122 2.519 1.455 峰态系数KU -0.558 7.208 10.570 2.894 偏态类型 负偏态 正偏态 正偏态 正偏态
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