The creep behaviors in deep underground engineering structures, especially in soft rocks, have a remarkable impact on the long-term stability of the excavations, which finally leads to the high risk and failure of it. Accordingly, it is essential to recognize the time-dependent deformation through the investigation of this phenomenon. In this study, the creep behaviors of soft rocks were examined to help understand the underlying mechanism of the extended time-dependent deformation. Due to the limited results about the time-dependent properties of the constituents of the rock that reveal their heterogeneity, the targeting nanoindentation technique (TNIT), was adopted to investigate the viscoelastic characteristics of kaolinite and quartz in a two-constituent mudstone sample. The TNIT consists of identifications of mineralogical ingredients in mudstone and nanoindentation experiments on each identified constituent. After conducting experiments, the unloading stages of the typical indentation curves were analyzed to calculate the hardness and elastic modulus of both elements in mudstone. Additionally, the 180 s load-holding stages with the peak load of 50 mN were transformed into the typical creep strain–time curves for fitting analysis by using the Kelvin model, the standard viscoelastic model, and the extended viscoelastic model. Fitting results show that the standard viscoelastic model not only can perfectly express the nanoindentation creep behaviors of both kaolinite and quartz but also can produce suitable constants used to measure their creep parameters. The creep parameters of kaolinite are much smaller than that of quartz, which causes the considerable time-dependent deformation of the soft mudstone. Eventually, the standard viscoelastic model was also verified on the quartz in a sandstone sample.

深层地下工程结构中的蠕变行为，特别是软岩中的蠕变行为，对开挖的长期稳定性产生重大影响，最终导致其高风险和高破坏性。因此，必须通过研究这种现象来识别随时间变化的变形。在这项研究中，研究了软岩的蠕变行为，以帮助理解随时间变化的变形的潜在机理。由于关于岩石成分随时间变化的特性有限的结果表明它们的不均匀性，因此采用靶向纳米压痕技术（TNIT）来研究两成分泥岩样品中的高岭石和石英的粘弹性特征。TNIT包括对泥岩中矿物成分的识别以及对每种已识别成分的纳米压痕实验。经过实验，分析了典型压痕曲线的卸载阶段，以计算出泥岩中两种元素的硬度和弹性模量。此外，使用开尔文模型，标准粘弹性模型和扩展粘弹性模型，将峰值载荷为50 mN的180 s保持载荷阶段转换为典型的蠕变应变-时间曲线，以进行拟合分析。拟合结果表明，标准粘弹性模型不仅可以完美表达高岭石和石英的纳米压痕蠕变行为，而且可以产生用于测量其蠕变参数的合适常数。高岭石的蠕变参数远小于石英的蠕变参数，这会导致软泥岩随时间的显着变形。最终，还在砂岩样品中的石英上验证了标准粘弹性模型。