单轴–三轴和渗透水压条件下砂岩应变特性的CT试验研究

SANDSTONE STRAIN PROPERTIES UNDER UNIAXIAL-TRIAXIAL COMPRESSIVE AND SEEPAGE PRESSURE CONDITIONS WITH CT TECHNIQUE

常规的应力应变试验难以清晰地反映砂岩在不同应力状态下的细观应变特性,然而,砂岩细观应变特性对一些工程的影响是非常巨大的。通过螺旋CT机以及与其配套的实时三轴加载和渗透压力设备对砂岩进行各种应力状态下的应变特性试验,反映出不同应力状态下的砂岩的应变特性有很大不同。结合CT图像和CT数的分析,对砂岩应变过程中的孔隙率的变化能直观地进行计算,以及对CT数方差的分析,能较简单地判断出砂岩的应变特性以及破坏模式。研究结果表明:(1)在单轴和三轴压力作用下,砂岩CT数方差变化剧烈的地方发生脆性变化,而方差比较稳定的地方发生塑性变化;(2)当有渗透水流作用时,砂岩应变特性与干砂岩的应变特性有明显差异,峰值强度显著增大,残余强度也明显增加;(3)砂岩在单轴干燥状态下是发生脆性破坏,而在有渗透压力和围压的情况下发生的是塑性破坏,有围压而没有渗透压作用时的破坏介于两者之间。

Understanding the deformation and fracturing processes is a key problem for rock engineering and earthquake prediction. Experimental rock deformation studies and structural analysis of exhumed fault zones have been used to investigate the mechanism of faulting and to develop models of fault evolution. Through the study which is based on devices including the multislice spiral CT（MSCT） and real-time loading machine and seepage machine, the strain properties of sandstone under uniaxial-triaxial compressive and seepage pressure conditions are found to be different from each other. With integrated analysis of CT images and CT number, the porosity randomly distributed in the stress process is calculated. Through the variant analysis of＇CT numbers, it is easy to know the strain properties and cracking patterns. When the variance of CT number is increasing rapidly, the strain and cracking pattern of sandstone is brittle. If the variance of CT number is stable or declines linearly slowly, the deformation and failure modes of sandstone are plastic. The strain properties under seepage pressure are different from others. The peak strength and residual strength of a sandstone increases remarkably under seepage pressure conditions. The dry sandstone crack is brittle under uniaxial compressive condition, When the compressive conditions are with seepage pressure and triaxial compression, the crack is on plasticity. With triaxial compressive without seepage pressure, the crack pattern is between the two patterns above. So, X-ray CT is a useful method for the study of the strain properties of sandstone under uniaxial-triaxial compressive and seepage pressure conditions.