Experimental study on dynamic compression of unsaturated calcareous sand
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摘要: 使用经过系统标定的霍普金森压杆试验装置对不同含水率钙质砂进行了在准一维应变条件下的动态压缩试验,试样的平均应变率为209~1 137 s−1。试验结果表明:半导体应变片灵敏系数和压杆弥散关系的标定对试验结果的准确性具有重要影响;当钙质砂应变小于0.025时潮湿试样的切向模量高于干燥试样,而在应变大于0.025时则相反;潮湿钙质砂的切线模量随含水率的增加先减后增。通过分析非饱和钙质砂在锁变后其轴向应力应变曲线及侧压力系数的变化规律,提出了非饱和钙质砂锁变现象的模型。Abstract: The dynamic compression tests of calcareous sands with different moisture contents under quasi-one-dimensional strain conditions were carried out using a calibrated SHPB system in the average strain rate ranging from 209 s−1 to 1137 s−1. The test results show that the calibration of the sensitivity coefficient of the semiconductor strain gauge and the dispersion of the pressure bar have a significant influence on the accuracy of the test results. When the strain of the calcareous sand is below 0.025, the tangential modulus of moist calcareous sand is higher than that of dry sand, but the opposite is true when the strain is above 0.025. The tangential modulus of moist samples decreases first and then increases with the increase of the water content. By analyzing the variation of axial stress-strain curve and lateral pressure coefficient of unsaturated calcareous sand after lock-in phenomenon, a model of the phenomenon of unsaturated calcareous sand is proposed.
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表 1 半导体应变片标定结果
Table 1. Calibration results of semiconductor strain gauges
信号类型 K1 K2 R2 入射杆压缩波 91.0 9 275 0.997 入射杆拉伸波 95.0 1 890 0.998 透射杆压缩波 93.6 4 500 0.998 透射杆拉伸波 97.1 1 537 0.999 表 2 SHPB试验工况表
Table 2. Test table of SHPB experiments
干密度/(g∙cm−3) 名义含水率/% 试验组编号 平均子弹速度/(m∙s−1) 平均应变率/s−1 1.40 1 CS001 21.43 1 128 CS002 9.78 487 CS003 4.02 335 1.40 10 CS101 18.52 1 118 CS102 9.03 551 CS103 3.62 242 1.40 20 CS201 18.04 1 137 CS202 9.01 533 CS203 3.61 209 1.40 30 CS301 18.14 836 CS302 9.13 522 CS303 3.56 243 表 3 非饱和砂土锁变现象试验结果的统计
Table 3. Experimental results of unsaturated sands with locking-up phenomenon
结果 $\dot \varepsilon $/s-1 (σz)max/MPa 砂土种类 Cu e0 Sr/% M/GPa R Veyera[12] 1 000 220 Eglin石英砂 3.41 0.51 60 3.32 0.56 80 2.85 0.44 180 Tyndall石英砂 1.18 0.654 80 3.65 0.82 211 Ottawa石英砂 1.5 0.545 80 3.24 0.86 Luo[34] 600 300 Quikrete 砂 2.33 0.55 64 — 0.68 85 — 0.59 Barr[13] 3 500 240 松散石英砂 2.2 0.77 25 3.17 1.02 52 3.35 1.01 本文 500 70 密实钙质砂 >6 1.01 57 — 1.02 86 2.34 1.11 注:$\dot \varepsilon $为应变率;Cu为不均匀系数;e0为初始孔隙比;Sr为试样饱和度;M为锁变模量。 -
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