微生物加固钙质砂压缩前后细观尺度变化试验研究

Experimental study of fine-scale changes in MICP-treated calcareous sand before and after compression

MICP是岩土工程领域新兴的一种环境友好型砂土加固技术,可以用于提高钙质砂的工程性能,但由于MICP加固钙质砂试样的复杂结构,需要对其细观尺度展开研究以解释宏观现象。运用CT扫描技术,对三轴压缩前后的微生物加固钙质砂试样进行三维重构,分析加载前后试样细观尺度变化。研究发现,使用CT扫描得到的二维灰度图像可以显示试样的孔隙分布,且在二维灰度图像的降噪处理过程中非局部均值滤波算法具有良好的降噪效果。在此基础上进行三维重构,结果表明,加载前试样孔隙主要分布在试样高度方向1/3处、2/3处及试样两端,加载后这部分区域的孔隙会有所增加,即加载过程中试样的破坏主要集中在试样本身已有的薄弱区域。在三维重构基础上分割显著破坏面,显示低应力水平下试样破坏模式为X共轭剪切破坏,而在高应力水平下的破坏模式为单斜面剪切破坏。

MICP is an emerging environmentally friendly sand reinforcement technique in the field of geotechnical engineering that can be used to improve the engineering performance of calcareous sands.However,due to the complex structure of MICP-treated calcareous sand specimens,more work needs to be carried out at the fine-scale to explain the macroscopic phenomena.This paper employs CT scanning to perform three-dimensional reconstruction of MICP-treated calcareous sand specimens before and after triaxial compression,and analyzes the fine-scale changes of the specimens.The results show that the two-dimensional grey-scale images obtained using CT scanning can demonstrate the pore distribution of the specimen,and the non-local mean filtering algorithm has a good noise reduction effect in the reduction process of the 2D grey-scale images.Based on this,3D reconstruction was conducted on the MICP-treated calcareous sand specimens.The results showed that before loading,the pores of the specimens mainly distributed at one-third,two-thirds,and both ends of the specimens in the vertical direction,and the pores in these parts of the specimens would increase after loading.It is indicated that the damage to the specimen during loading mainly concentrated in the existing weak areas of the specimen itself.Segmentation of significant damage surfaces on the basis of 3D reconstructions shows that the damage mode of the specimen at low stress levels is X-conjugate shear damage,while at high stress levels the damage mode is of single bevel shear damage.