砂岩矿物组分流变特性纳米压痕实验研究

深部地下工程中,关于岩石流变特性对工程结构施工设计和稳定性的显著影响研究较多,但主要是基于宏观非均质岩样进行的,很少涉及岩石细观尺度上的矿物流变特性。采用纳米压痕技术研究砂岩中矿物组分的流变特性和本构方程,结合X射线衍射(XRD)、扫描电子显微镜(SEM)和能谱仪(EDS)获得的矿物组分分布特征,砂岩中石英、钠长石、方解石和高岭石的弹性模量分别为87.74,59.85,32.30和17.31GPa,体现了砂岩的细观非均质性。砂岩的纳米压痕细观流变过程包括瞬时弹性变形、蠕变和弹性后效,可以采用伯格斯模型进行描述。在细观流变变形过程中,蠕变荷载保持阶段和卸载阶段会加剧矿物中孔、裂隙发育,使得拟合弹性后效获得的流变力学参数明显小于拟合蠕变过程获得的结果。砂岩宏观流变弹性参数可以通过细观矿物组分流变弹性参数尺度升级获得,为流变力学特性研究提供了一种方便、高效的方法。

Rheological characteristics of mineral components in sandstone based on nanoindentation

In deep underground engineering,the rheological characteristics of rock can affect the construction design and stabilities of engineering structures,which has been extensively investigated. However,the previous studies mainly focused on large inhomogeneous rock samples and ignored the rheological characteristics of minerals in them at the meso-scale. Consequently,in this study,the rheological characteristics and constitutive model of various minerals in sandstone were investigated by using the nanoindentation technique. The distributions of minerals were obtained by using X-ray diffraction(XRD),scanning electron microscope(SEM) and energy dispersive spectrometer(EDS). The elastic moduli of quartz, albite, calcite and kaolinite from nanoindentation experiment are respectively 87.74,59.85,32.30 and 17.31 GPa,indicating the heterogeneity of the sandstone at the meso-scale. The nanoindentation rheological process consists of instantaneous elastic deformation,creep and elastic aftereffect,which can be described by the Burgess model. During the rheological process,the creep load-holding and unloading periods inevitably make the pores and cracks in the minerals develop,which aggravates the deformation during elastic aftereffect and yields smaller rheological parameters than those obtained from the creep. The macro-scale rheological elastic parameters of sandstone can be obtained by upgrading the rheological elastic parameters of its mineral components at the meso-scale,which provides a convenient and efficient method for studying the rheological properties of sandstone.