不同围压和层理下板岩三轴蠕变试验及损伤模型研究

Triaxial creep experiment and damage model for slate under different confining pressures and beddings

为了研究围压和层理对板岩三轴蠕变特性的影响,制备了最大主应力方向与层理夹角为0°和90°的2组岩样(0°为平行组;90°为垂直组),分别进行5 MPa、10 MPa、15 MPa围压下的三轴蠕变试验。结果显示:板岩在三轴应力条件下的蠕变具有瞬时弹性阶段、稳定蠕变阶段、加速蠕变阶段这三个阶段特征;在同一围压下,垂直组试样加载级数大于平行组岩样加载级数;垂直组试样的瞬时弹性应变高于平行组试样;垂直组试样的累计蠕变应变均低于平行组试样。计算长期强度与峰值强度的比值得到垂直组试样的强度损伤低于平行组试样;围压越高,试样蠕变变形越小,峰值强度和长期强度越高。基于Kachanov蠕变损伤理论,考虑层理角度的损伤,引进一个弹塑性损伤元件,建立了描述不同层理角度板岩蠕变过程的改进西原模型,用该模型对试验数据进行拟合,结果表明:模型能够较好地反映蠕变三阶段;垂直组试样的弹性模量、黏滞系数比平行组试样相对较大,蠕变参数基本随着围压的增大而增大,体现了围压效应,这与试验结果相吻合。

In order to study the influences from confining pressure and bedding on the triaxial creep properties of slate,two groups of rock specimen(0°for parallel group and 90°for vertical group)with the maximum principal stress direction and be-dding angle of 0°and 90°are prepared,and then the triaxial creep experiments under the confining pressures of 5 MPa,10 MPa and 15 MPa are carried out respectively.The results show that creep of slate under triaxial stress has the characteristics of three phases,i.e.instantaneous elastic phase,stable creep phase and accelerated creep phase.Under a same confining pressure,the loading series of the vertical group of specimen is larger than that of the parallel group of specimen,while the instantaneous elastic strain of the vertical group of specimen is higher than that of the parallel group of specimen and the cumulative creep-strain of the vertical group of specimen is lower than that of the parallel group of specimen.It is obtained from the ratio between the long-term strength and the peak strength that the strength damage of the vertical group of specimen is lower than that of the parallel group of specimen,while the higher the confining pressure is,the creep-deformation is to be less and both the peak strength and the long-term strength are to be higher.Based on the Kachanov′s creep damage theory and under the consideration of the damage of bedding angle,an improved Nishihara′s model for describing the creep-processes of the slates with different bedding angles is established through introducing an elastic-plastic damage element,and then the relevant experimental data are fitted with the model,from which the results show that the model can better reflect the three phases of the creep and the creep parameters are basically increased along with the increase of the confining pressure,thus the effect of confining pressure is embodied,which is consistent with that from the experiment result.