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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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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