蠕变作用后大理岩强度与变形特性试验研究

Experimental study on strength and deformation characteristics of marble after creep

为研究蠕变行为对岩石力学性质的影响,分别在裂隙压密阶段、弹性阶段、裂隙稳定扩展阶段和非稳定扩展阶段,对大理岩进行不同应力水平和时间的蠕变预处理,卸载后再进行单轴压缩破坏试验,分析不同条件蠕变作用后大理岩强度与变形特性的变化规律,同时提出采用体变速率进行岩石变形阶段划分的新方法。结果表明:(1)裂隙压密和弹性阶段蠕变对大理岩力学性能起强化作用,随蠕变时间增长,强度和弹性模量增大,泊松比减小,且弹性阶段蠕变的强化程度大于压密阶段。裂隙稳定扩展阶段蠕变呈现相反的变化规律,起劣化作用,而岩样在非稳定扩展阶段蠕变预处理时快速破坏;(2)依据扩容速率可将岩石变形过程分为3个阶段,分别为平稳压缩阶段、加速扩容阶段及减速扩容阶段;(3)裂隙压密和弹性阶段蠕变后,大理岩峰值扩容速率随蠕变时间增长略有减小,裂隙稳定扩展阶段蠕变后则随蠕变时间增长显著增大;(4)原始岩样和蠕变作用0 h后岩样的单轴压缩破坏形态以单一剪切面破坏为主。随蠕变时间增长,裂隙压密和弹性阶段蠕变后岩样破坏形态转为沿轴向劈裂破坏,裂隙稳定扩展阶段蠕变后转为剪切、劈裂组合破坏,除几条主裂隙外,还伴随众多次生裂隙。

In order to investigate the effect of creep behavior on the strength and deformation of rock,a number of marble samples were pretreated under different hours of creep preloading at different stress levels which contains the compaction stage,elastic stage,stable stage of crack growth,unstable crack growth and failure stage on the whole stress-strain curves. After the creep loading,the samples were reloaded under uniaxial compression to analyze the influence of creep behavior on the strength and deformation of marble. Meanwhile,a new method was proposed to divide the stages of volume strain using the volumetric strain rate. The creep at the stress levels of the compaction stage or the elastic stage enhances the mechanical performance of marble. With the creep time increases,the uniaxial strength and elastic modulus increase but Poisson’s ratio decreases. The enhanced degree of mechanical performance of creep is greater at the elastic stage than at the compaction stage. In addition,the failure of the rock samples occurs in a short time if the creep is conducted at the unstable crack growth or failure stage. The deformation process of the rock can be divided into three stages according to the dilatation rate,a stable compaction stage,an accelerated dilatation stage and a decelerated dilatation stage. After going through the creep preloading at the compaction stage or the elastic stage,the dilatation rates of marble samples decrease slightly with the increasing in creep time. On contrary,after going through the creep preloading at the stable crack growth stage,the dilatation rates increase dramatically with the creep time increases. The failure patterns of marble samples without creep preloading under uniaxial compression are mainly shear failure with a single macrocrack. With the increasing of the creep time,the failure patterns of marble samples underwent creep preloading at the compaction stage or the elastic stage were gradually transformed from shear failure to splitting failure. The failure patterns of marble samples underwent creep preloading at the stable crack growth gradually transform to the mixed mode of shear and splitting failures,accompanied by several principal cracks and numerous associated cracks.