大位移剪切下钙质砂破碎演化特性

为了揭示钙质砂在大位移剪切作用下的破碎及形状演化规律，对南海钙质砂进行了系列不同剪切位移下的环剪试验。首先，利用筛分和激光粒度分析获取试验后的颗粒粒径分布，分析颗粒分布变化情况；其次，通过粒径分布对破碎进行定量分析；最后，运用图像处理技术计算颗粒圆度和扁平度，分析了颗粒形状的变化情况。试验结果表明，在不同的竖向压力下，颗粒会达到不同的稳定级配，但达到稳定所需的剪切位移相同；经历大位移剪切后，出现粒径为0.01～0.075 mm钙质砂破碎严重的现象；随剪切位移的增加，颗粒的圆度和扁平度减小。针对细小颗粒破碎严重的现象，修正了相对破碎率；修正后的相对破碎率能考虑粒径为0.01～0.075 mm颗粒发生的破碎。剪切后的钙质砂颗粒更为规则，整体轮廓趋于圆形、表面更光滑。

Evolution of particle breakage of calcareous sand under large displacement shearing

To reveal breakage behavior and deformation of particle shape for calcareous sand from the South China Sea with large shearing displacement, a series of ring shear tests was performed under controlled shear displacement. After ring shear, the particle size distributions of the samples were obtained by the sieving method and laser grain-size analyzer. The particle breakage was quantitatively examined by analyzing particle size distribution. The roundness and flatness was also analyzed to examine the variation of particle shape using the image processing technology. Experimental results indicate that shearing under different vertical pressures would lead to different stable graduations. However, the stable graduation is observed under the same shearing displacement. Severe breakage occurs in the samples with particle sizes of 0.01-0.075 mm after large displacement shearing. With the increase of the shear displacement, the roundness and the flatness of particles decrease. The relative breakage is modified to account for the severe breakage of fine grains (<0.075 mm) in large displacement shearing. The modified relative breakage ratio can cover the breakage of the particles with sizes of 0.01-0.075 mm. After large displacement shear, the shape of calcareous sand tends to be more regular, more rounded and smoother.