三轴压缩条件下基于CT实时监测的冻结兰州黄土细观损伤变化研究

Study of Meso-Damage Changes of Frozen Lanzhou Loess under Triaxial Compression Based on CT Real-Time Monitoring

在1 MPa围压下,对不同温度条件下的冻结兰州黄土三轴压缩试验过程进行CT动态扫描,获得了由CT数表示的土体损伤量表达式.结果表明:冻结兰州黄土最初在围压作用下,试样沿径向方向被压缩,导致试样轴向伸长;低温冻结试样的弹性变形持续时间长于高温试样,如-2.3℃试样在应变达到0.32%时即开始屈服进入塑性变形,而-7℃试样的屈服应变值达到了1.33%;试样塑性变形阶段持续较长时间,即使样品轴向变形达到了20%,试样截面积有了显著增大,但偏应力仍在持续增大;各试样整体损伤量基本都在0.1以下,相对于单轴受力状态下试样的损伤度要小得多,故围压对于冻土试样有"抗损伤"的功效.随着应变与偏应力的增大,损伤量也不断增大;对不同温度的试样而言,要产生相同的损伤,低温试样需要的偏应力远比高温试样需要的偏应力大.

Under 1MPa confining pressure, a series of CT scanning tests were performed on frozen Lanzhou loess with different temperatures under triaxial loading condition. The soil damage variable expressed by CT number was obtained and the following conclusions can be drawn. At the beginning of loading confining pressure, the specimen is compressed along the radial direction, leading to axial elongation of the specimen; the duration of elastic deformation of the specimen at low temperature is more longer than that at higher temperature, i. e. , at -2. 3 ℃, when it reaches a strain of O. 32%, the specimen will yield to the plastic deformation, and at - 7 ℃, it is necessary to reach a strain of 1.33%. The stage of plastic deformation of the specimen will last for a long time, even if the specimen has reached 20% of axial deformation, the specimen cross-sectional area will significantly increase, with deviatoric stress increasing continuously. The total damage amount of each specimen is lower than 0.1, much smaller than that under uniaxial stress state. So the confining pressure is able to ＂ endure damage＂. With the increase of strain and deviatoric stress, damage amount is increasing. Specimen at low temperature requires de- viatorie stress more than that at high temperature for reaching the same damage.