膏岩三轴压缩试验及高温相变特征研究

Study of gypsum rock triaxial compression experiment and characteristic of high temperature phase transition

采用伺服刚性试验机对天然膏岩开展三轴压缩试验,研究了温度及围压对膏岩强度及变形特性的影响。结果表明,膏岩在不同围压下均具有良好的塑性流动特性,加载后无明显的剪切破坏面,而是出现明显的侧向膨胀。根据三轴试验结果,利用摩尔-库仑定律得到了膏岩的强度准则及抗剪强度参数。升高温度导致膏岩强度降低,且高温下石膏发生晶型转变,从二水石膏脱水转变为半水石膏,利用扫描电镜和X衍射对此过程进行了研究。脱水过程导致瞬间孔隙应力增加,膏岩破坏特性由延性转变为脆性。随着持续加载,破裂断面逐渐愈合。膏岩显著的塑性流动能力及快速的裂隙愈合能力对于天然气盖层的封闭稳定性具有重要意义。

Experiments are carried out to study the influences of temperature and confining pressure on natural gypsum rock strength and deformation properties under triaxial compression using servo-controlling testing machine.The results indicate that gypsum rock has obvious plastic flow property under different confining pressures.There is no obvious shear failure surface but lateral dilation is observed.Based on Coulomb-Mohr theory,the strength criterion and shear strength parameters of gypsum rock are obtained.With the increase of temperature,the strength of gypsum decreases.At high temperature,gypsum dehydration process takes place with result of transformation from gypsum to bassanite.Scanning electron microscope（SEM） and X-ray diffraction（XRD） methods are used to study the process.With the dehydration process,the pore pressure increases and the failure property becomes brittle.With load continuing,failure surface tends to heal.Obvious plastic flow characteristic and fast self-healing property of gypsum rock are fundamental to sealing stability of natural gas caprock.