千枚岩碎屑土三轴试验剪切带扩展性状的CT研究

土体剪切带的产生和发展是岩土工程界一直关注的问题。对千枚岩碎屑土进行了固结排水剪切试验,并在试验过程中采用CT可视化技术进行了实时监测扫描,得到同一断面位置不同应变条件下的系列CT切片,从CT切片中可观测到试样随应变的增加而出现的明显的剪切带。采用CT技术真实再现了三轴试样在轴向力作用下,局部裂纹扩展逐渐贯穿形成完整剪切带的过程。对CT切片进行了7个区域的CT数平均值和CT数标准差统计,分析认为,轴向应变在3%~10%范围内是剪切带形成和发展的主要阶段,在应变3%前试样主要被压缩,在应变3%后试样在偏应力的作用下逐渐出现微裂隙,并随应变的增加,微裂隙越来越明显。CT数统计值出现微裂隙的应变和宏观观测到微裂隙的应变不对等,在判断剪切带微裂隙出现应变上建议以CT数统计值为准值。

Expansion mechanism of shear bands in phyllite detritus soil by CT technology

The emergence and development of soil shear bands is one of the concerned problems of geotechnical engineering. Consolidation drained shear tests on phyllite detritus soils are conducted, and the real-time monitoring scan is performed in the test process by using the CT technology. A series of CT pictures at the same section position are obtained under different strain conditions. It can be observed that the shear band obviously appears in the specimen with the increase of strain from CT slices. Using the CT technology, the process from local crack to form the complete shear bands of specimen is reproduced under the axial force. Through the analysis of the average value of CT number and standard deviation of 7 regions in the CT pictures, it can be found that the range of axial strain of 3%~10% is the main stage for formation and development of shear band . The specimen is mainly compression when the strain is below 3%, but when the strain is over 3%, the specimen gradually shows local crack under the deviatoric stress, and the crack is more and more obvious with the increasing strain. The strain is not equal between the CT statistical values and macro cracks through macroscopic observation. It is suggested that the CT statistical values should be regarded as the criterion to determine the strain of micro cracks in the shear band.