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EXPERIMENTAL STUDY OF ACOUSTIC EMISSION CHARACTERISTICS DURING ONE-DIMENSIONAL COMPRESSION REBOUND OF CALCAREOUS SAND
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摘要: 为了揭示钙质砂在一维压缩回弹作用下的压缩变形、颗粒破碎特性以及声发射规律，对钙质砂进行了3种相对密实度下不同粒组的一维压缩回弹实验和声发射实验。通过对不同粒组、不同相对密实度的钙质砂进行一维压缩实验和同步的声发射实时监测，获得其压缩、回弹和声发射特性，最后通过筛分获得实验后的颗粒粒径分布，得出相对破碎势Br。实验结果表明：钙质砂的压缩变形由颗粒位置调整和破碎两部分组成，其中颗粒破碎是产生压缩变形的主要因素，回弹曲线近似一条直线，表明压缩变形为不可恢复的塑形变形；压力相同时颗粒粒径越大，相对破碎势Br越大。颗粒形状不同致使颗粒间填充作用与嵌合作用不同，影响颗粒的滑移与重排列，进而影响颗粒的压缩变形。两种砂的声发射计数率随粒径增大而增大，且都集中出现在800~3200 kPa的压缩阶段，钙质砂的压缩变形及破碎特性与其声发射特征具有一致性，钙质砂声发射计数率与时间关系曲线和应力与时间关系曲线吻合较好，可通过声发射计数率与时间关系曲线来反映钙质砂的力学特性。钙质砂存在一个声发射事件最少的“临界孔隙比”，本次实验中1~2 mm钙质砂临界孔隙比为1.33~1.41，试样的初始孔隙比偏离该临界值时，声发射活动会有不同程度提高。Abstract: This paper aims to reveal the compressive deformation,particle breakage characteristics,and acoustic emission laws of calcareous sand. The one-dimensional compression-resilience tests and synchronous acoustic emission tests were carried out on calcareous sand with different particle size fractions under three different relative densities. By sieving analysis,the relative breakage(Br) was obtained based on the particle size distribution after the test. The experimental results showed that the compressive deformation of calcareous sand is caused by the particle rearrangement and particle breakage. The particle breakage is the major factor behind this phenomenon. The rebound curve is approximately a straight line,indicating that the compressive deformation is an irreversible plastic deformation. Under the same stress,the larger the particle size,the greater the Br. The different shapes of the particles result in different interparticle filling and interlocking effects,which affects the sliding and rearrangement of the particles,and then influences the compressive deformation of the particles. The acoustic emission counts rate of the two kinds of sand increases with the increase of the particle size,and both appear mainly in the compression phase between 800 kPa and 3200 kPa. The compressive deformation and breakage characteristics of calcareous sand are consistent with their acoustic emission laws. The relation curves between counts rate and time are in good agreement with the stress-time curves. The mechanical characteristics of the calcareous sand can be reflected based on the counts rate-time curves. For calcareous sand,a "critical void ratio" exists with the fewest acoustic emission events. In this study,its value of calcareous sand with a particle size of 1~2 mm is 1.33~1.41. When the initial void ratio of the sample deviates from this critical value,the acoustic emission activities would increase in varying degrees.
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Key words:
- Calcareous sand /
- Acoustic emission /
- One-dimensional compression /
- Particle breakage
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图 1 钙质砂各粒组图
a. 0.5~1 mm；b. 1~2 mm；c. 2~5 mm；d. 2~5 mm片状；e. 2~5 mm枝棒状；f. 2~5 mm块状
Figure 1. Each grain group diagram of calcareous sand
图 5 1~2 mm不同相对密实度的e-p曲线
Figure 5. 1~2 mm e-p curves with different relatively tightness
图 6 2~5 mm不同形状钙质砂的e-p曲线
Figure 6. 2~5 mm e-p curves of 2~5 mm calcareous sand in different shapes
图 7 钙质砂不同粒组压缩回弹后的级配曲线
Figure 7. The distribution curves of calcareous sand different grain groups after compressed and rebounded
图 8 2~5 mm不同形状钙质砂压缩回弹后级配曲线
Figure 8. The distribution curves of different shapes of 2~5 mm calcareous sand after compression and rebound
图 9 钙质砂、标准砂不同粒组声发射计数率、应力与时间曲线
a. 0.5~1 mm钙质砂；b. 1~2 mm钙质砂; c. 2~5 mm钙质砂；d. 1~2 mm标准砂；e. 2~5 mm标准砂
Figure 9. Acoustic emission count rate, stress and time curve of calcareous sand and standard sand of different particle groups
图 10 钙质砂、标准砂不同粒组声发射幅值、应力与时间曲线
a. 0.5~1 mm钙质砂；b. 1~2 mm钙质砂；c. 2~5 mm钙质砂；d. 1~2 mm标准砂；e. 2~5 mm标准砂
Figure 10. Acoustic emission amplitude, stress and time curve of calcareous sand, standard sand of different particle groups
图 11 钙质砂1~2 mm不同密实度声发射率、应力与时间曲线
Figure 11. Acoustic mission count rate, stress and time curve of 1~2 mm calcareous sand under different densities
a. Dr=60%; b. Dr=70%; c. Dr=80%
图 12 钙质砂1~2 mm不同密实度声发射幅值、应力与时间曲线
Figure 12. Acoustic emission amplitude, stress and time curve of 1~2 mm calcareous sand under different densities
a. Dr=60%; b. Dr=70%; c. Dr=80%
图 13 粒组、相对密实度Dr与相对破碎势Br的关系
Figure 13. The relationship between the relatively dense(Dr), and the relatively fragmented potential(Br) of different granular groups
图 14 钙质砂、标准砂压缩(回弹)指数Cc(Cs)
Figure 14. Compression(rebound) index Cc(Cs) of calcareous sand and standard sand
图 15 2~5 mm钙质砂不同形状相对破碎势
Figure 15. The relative breakage potential of 2~5 mm calcareous sand with different shapes
表 1 试样的基本物理参数
Table 1. The basic physical parameters of the sample
试验材料 粒径/mm Gs ρd，max/g·cm-3 ρd，min/g·cm-3 钙质砂 0.5~1 2.82 1.32 1.06 1~2 1.31 0.97 2~5 1.30 0.90 标准砂 1~2 2.68 1.54 1.25 2~5 1.61 1.30 
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