Creep property is an important mechanical property of rocks. Given the complexity of rock masses, mechanical parameters change with time in the creep process. In this work, a nonlinear function for describing the time-dependent change of parameters was introduced and an improved variable-parameter nonlinear Nishihara shear creep model of rocks was established. By creating rock-like materials, the mechanical properties of rocks under the shear creep test condition were studied, and the deformation characteristics and long-term shear strength of rocks during creep were analyzed. The material parameters of the model were identified using the creep test results. Comparison of the model’s calculated values and experimental data indicated that the model can describe the creep characteristics of rocks well, thus proving the correctness and rationality of the improved model. During shear creep, the mechanical properties of rocks have an aging effect and show hardening characteristics under low shear stress. Furthermore, according to the fact that Gk of the nonlinear model can characterize the creep deformation resistance, a method to determine the long-term shear strength is proposed.
The creep characteristics of joint have an important influence on the long-term stability of rock mass engineering such as tunnels and slopes. In this paper, the sawtooth angle α is taken as the variable, five different numerical models of regular sawtooth joints are established using the discrete element numerical method, to study the shear mechanical characteristics of joints under creep condition. In addition, the shear mechanical properties of joints under transient condition are compared to analysis the influence of creep on the mechanical characteristics of joint. The results show that under shear creep condition: (1) Shear displacement of joint increases stepwise with time. At low sawtooth angles, the difference of joint shear displacement with different normal stresses is large. The long-term shear strength of joint is proportional to normal stress and sawtooth angle. (2) The total absorbed energy U and elastic energy Ue of the joint both increase as the sawtooth angle α increases. Dissipated energy Ud tends to increase first and then decrease with increasing sawtooth angle. Compared with the energy characteristics under transient condition, it is found that the joint under creep condition not only has a lower shear strength, but also requires less total absorbed energy and dissipative energy, and fewer cracks at critical failure. (3) Before the peak strength, the damage variable D increases nonlinearly with the shear displacement. Compared with the transient condition, the damage amount corresponding to the peak strength under the creep condition is smaller, and the evolution rate of the damage variable D with shear displacement at the critical failure is higher.
The Xi’an region of China has been suffering from groundwater depletion, ground fissure hazards, and surface subsidence for a long time. Due to the complex tectonics and frequent human and natural activities, land deformation in the region is aggravated, posing a threat to infrastructure and human life. This study adopted the multi-orbit and multi-temporal InSAR technology to measure multi-dimensional displacements and time-series displacements in Xi’an City. Through the multi-dimensional deformation verification, it was found that the control of groundwater flow direction by ground fissures is the cause of horizontal deformation. On the contrary, the flow direction of groundwater from west to east was inferred using multi-dimensional deformation. Further analysis was performed by calculating the deformation gradient of the cumulative deformation to obtain differential land subsidence and angular distortions, and it was quantitatively determined that the threshold for the generation of ground fissures caused by differential subsidence is 1/500. Then, through the mutual verification of the time series data and the groundwater level, a positive correlation was obtained. However, due to the inconsistent geological conditions and soil layers at the monitoring positions of Well 2 and Well 3, the lag time was 64 days and 4 days, respectively. Finally, the relationship between the surface deformation and the groundwater in the sustained uplift areas was explored. The Well 1 groundwater-level data with a monitoring period of 22 years and the corresponding monitoring points’ time series data were modeled; it was concluded that, in the future, the groundwater level will continue to rise and surface deformation will mainly increase, without a slowing trend. Therefore, research on the impact of surface uplift on infrastructure should be strengthened. By quantifying the relationship between land subsidence, ground fissures, and the groundwater level in Xi’an, the results of this study provide a reference for groundwater monitoring and management.
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