Taking the Gubei Mine as the research object, indoor uniaxial creep tests were carried out at temperatures of -5, -10, and -15 degrees C under loads of 0.3, 0.5, and 0.7 sigma s to study the creep characteristics of deep soil, Based on the Burgers rheological model and the auxiliary formula of viscoelastic rheological formula, the freezing pressure under the combined action mechanism of frozen wall, outer shaft wall and polystyrene foam board was theoretically analyzed. The results show that the creep deformation of frozen clay under a certain constant stress loading changes with time. At three temperatures, the creep is attenuated creep under constant stress of 0.3 and 0.5 sigma s; it exhibits non-attenuated creep at a constant stress level of 0.7 sigma s, and the growth rate increases over a certain period of time, and finally it is destroyed by excessive deformation over time. The calculated value of the freezing pressure calculated by the frozen wall model is roughly the same as the development law of the measured value, and the calculated value of the theoretical value of the freezing pressure is slightly larger than the measured value, indicating that the calculated value can be an effective reference for the creep of the frozen wall and can provide a guarantee for the construction safety.

Fractional calculus is a powerful mathematical tool for solving mechanical modeling problems. It is used to simulate soils between ideal solids and fluids. Using Riemann-Liouville's fractional calculus operator and theory, fractional order viscous element, nonlinear viscous element and viscoplastic body are connected in series to establish a fractional nonlinear creep damage model, which is used to simulate the nonlinear gradient process of rock creep under different water content conditions. The constitutive equation of the model is constructed. The parameters of creep damage model are identified based on the principle of least squares. The results show that the correlation between theoretical model and experimental data is more than 0.98, which can simulate the creep characteristics of rock well. The effect of model parameters on deformation is further explored, so that the effectiveness of model parameters can be analyzed and verified, and the applicability of the model in other complex stress environments is increased. The research results can provide theoretical basis for stability analysis and disaster prevention of soft rock slopes.

The investigation on damage creep properties of rock under freeze-thaw conditions are essential for assessing the long-term stability of rock mass engineering in cold regions. This research analyzed the damage characteristics of rock under the coupled effect of freeze-thaw cycles and loading; the damage variable under the coupled effect of freeze-thaw cycles and loading was proposed. A damage creep constitutive model was developed, and the determination method for the model parameters was proposed. The rationality of the model was calibrated using test data, and the calculation results of the proposed model were compared with classical Nishihara model. Additionally, the research analyzed the variation of model parameters with the number of freeze-thaw cycles and discussed the damage creep mechanisms of rock under the coupled effect of freeze-thaw cycles and loading.

Understanding the anisotropic creep behaviors of shale under direct shearing is a challenging issue. In this context, we conducted shear-creep and steady-creep tests on shale with five bedding orientations (i.e. 0 degrees, 30 degrees, 45 degrees, 60 degrees, and 90 degrees), under multiple levels of direct shearing for the first time. The results show that the anisotropic creep of shale exhibits a significant stress-dependent behavior. Under a low shear stress, the creep compliance of shale increases linearly with the logarithm of time at all bedding orientations, and the increase depends on the bedding orientation and creep time. Under high shear stress conditions, the creep compliance of shale is minimal when the bedding orientation is 0 degrees, and the steadycreep rate of shale increases significantly with increasing bedding orientations of 30 degrees, 45 degrees, 60 degrees, and 90 degrees. The stress-strain values corresponding to the inception of the accelerated creep stage show an increasing and then decreasing trend with the bedding orientation. A semilogarithmic model that could reflect the stress dependence of the steady-creep rate while considering the hardening and damage process is proposed. The model minimizes the deviation of the calculated steady-state creep rate from the observed value and reveals the behavior of the bedding orientation's influence on the steady-creep rate. The applicability of the five classical empirical creep models is quantitatively evaluated. It shows that the logarithmic model can well explain the experimental creep strain and creep rate, and it can accurately predict long-term shear creep deformation. Based on an improved logarithmic model, the variations in creep parameters with shear stress and bedding orientations are discussed. With abovementioned findings, a mathematical method for constructing an anisotropic shear creep model of shale is proposed, which can characterize the nonlinear dependence of the anisotropic shear creep behavior of shale on the bedding orientation. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).