压-拉循环荷载作用下红砂岩蠕变特性

Creep behavior of red sandstone under uniaxial cyclic compression and tension loading

利用自制岩石杠杆式拉压蠕变试验仪,对红砂岩进行2种恒定循环荷载蠕变试验以及等增量循环蠕变实验,分析各应力水平下的蠕变特征,研究岩石蠕变与循环次数之间的规律,探讨蠕变参数与循环次数之间的关系。研究结果表明:在各级恒定荷载作用下,试样变形均包含明显的瞬时应变和衰减蠕变及稳态蠕变,在1.19 MPa拉伸荷载作用下岩样出现加速蠕变。在50%σc-50%σt循环荷载作用下,岩样最大轴向应变逐渐增大,最大横向应变均逐渐减小,试样整体"缩短"而无明显扩容;85%σc-85%σt强度荷载使得岩样最大轴向与横向应变随着循环次数增加而增大,不仅表现为轴向"缩短",而且出现体积扩容;在2种恒定压-拉荷载作用下,试样均产生一定的残余永久变形,较大荷载使得试样轴向与横向残余永久应变均随循环次数增加而增加,而较小荷载作用下试样横向应变随循环次数增加而减小;试样蠕变随着增量循环荷载等级增加而增加,且产生一定的永久残余应变;施加32.59 MPa压应力后试样出现最大体积压缩应变,后体积逐步开始扩容。Burgers蠕变模型可以较好地反映红砂岩在恒定循环荷载作用下的蠕变特性,试样在经历3~4次循环后材料属性随循环次数及时间进一步劣化,最终在第5次循环时发生拉伸破坏。

To study the creep behavior of sandstone,two constant tension and compression cyclic loading creep tests and an incremental tension and compression cyclic creep test of red sandstone were conducted by using self-made rock leveraged tensile and compressive creep tester.Creep behavior of red sandstone at each stress level was analyzed,and the relationship between creep deformation and cycle times was studied.Relationships between creep parameters and cycle times were also discussed.The results show that deformation of red sandstone at each stress level contains significant instantaneous strain,decay creep strain and steady creep strain.The creep and failure accelerates at 1.19 MPa tensile load.At 50%σc-50%σt strength level,the maximum axial strain of sample increases and the maximum lateral strain decreases with the cycle times,and the sample overall presents“shortening”and has no obvious expansion.At 85%σc-85%σt strength level,the maximum axial and lateral strain of sample increase with cycle times,and the sample not only presents axial“shortening”but also volume expansion.The sample experiences residual permanent deformation at two different constant stress levels,and the axial and lateral residual permanent strain of the specimen increases with the cycle times at larger stress level,while the lateral strain decreases with cycle times at smaller stress level.Creep value of the sample increases with the increase of the load level,and a certain degree of permanent residual strain is generated.The sample presents the maximum compressive volume strain at compression stress level of 32.59 MPa and then its volume increases gradually.Burgers creep model can better reflect creep behavior of red sandstone under constant cycle loading.After cyclic compression and tension loads for 3-4 times,material properties of rock sample further deteriorate with cycle times and the sample finally presents tensile failure in the fifth cycle time.