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Regarding the issue of creep characteristics of the rock mass following excavation or excavation with graded loading and unloading under external forces. This study performs uniaxial compression and step loading and unloading creep tests on rock samples under different wetting-drying cycles with yellow sandstone to investigate the creep characteristics of rock bodies after excavation or excavations with step loading and unloading under external forces. Moreover, it constructs a creep damage model based on the nonlinear rheological theory and damage mechanics to describe the instantaneous elastic strain, instantaneous plastic strain, nonlinear viscoelastic strain, and nonlinear viscoplastic strain of rocks. Besides, it proposes a creep model parameter identification method based on the creep curve characteristics. The results have shown that the action of wetting-drying cycles causes a weakened decrease in elastic modulus, uniaxial compressive strength, and long-term compressive strength of yellow sandstone, in line with the exponential function change relationship. The specimen damage type evolves from shear damage of a single oblique section to conical shear damage of a double oblique section. Additionally, the creep rate is not constant in the steady-state creep stage but constantly changes with time, and the fluctuation range increases with the increase in the wetting-drying cycles. The creep damage model parameters do not differ much under the same stress condition, and each parameter is influenced by the creep stress at a specific law. The instantaneous modulus of elasticity of the elastomer and plastic body and the creep stress have a linear relationship, whereas the modulus of elasticity and viscosity coefficient and the creep stress have an exponential one. [ABSTRACT FROM AUTHOR]

The cyclic water intrusion and stresses lead to changes in the rock pores' microstructure, which affects the rock’s seepage characteristics. This study performs a three-dimensional reconstruction of the rock specimen using the Avizo software based on the results of multiple computed tomography (CT) tests conducted on sandstone subjected to varying numbers of cyclic water intrusions. In addition, a numerical model comprising pores and grain matrix is developed, based on which stress loading and seepage simulations are carried out. The results show that the mean outlet velocity, maximum seepage pressure, and permeability of the rock samples show an exponential increase with the number of cyclic water intrusions. Stress loading of the rock samples reveals that as the stress increases, the average exit velocity and permeability decrease. It is observed that the stress sensitivity index tends to increase and subsequently decrease with the number of water intrusion cycles at the same stress level when the stress sensitivity index is calculated under different water intrusion cycles. The relationship between effective stress, porosity, and stress sensitivity index is derived, and an effective linkage between permeability and macro-mechanical parameters considering stress sensitivity is achieved. [ABSTRACT FROM AUTHOR]

PVDF-based gas diffusion electrode is synthesized in two steps: first, PVDF-based gas diffusion layer is produced by phase inversion and subsequently the product is electrochemically polymerized with polypyrrole and reduced graphene oxide. The manufactured GO@Pr@GDE toward O2 reduction reaction is studied as air cathode to generate H2O2, which can be further used to oxidize nonbiodegradable ofloxacin in a simple cell system. Although all the GDE samples have a similar configuration, GO@Pr@GDE shows the highest catalytic activity toward H2O2 production. The exchange current density of GO@Pr@GDE in Na2SO4 solution is 2.4 × 10−8 A cm−2, which is 6 times greater than that of Pr@GDE. Results of XRD, FTIR, and SEM characterization are consistent with GDE's electrochemical behavior, revealing that pyrrole polymerized on the pristine PVDF-based GDE can supply more conductive sites, and reduced GO plays the most important role in H2O2 production and achieving 69% removal efficiency of ofloxacin. [ABSTRACT FROM AUTHOR]