Influence of Ambient Humidity on the Creep Properties of Rock Masses and Establishment of a Creep Damage Constitutive Model

To investigate the effects of high humidity on the instantaneous and creep mechanical properties of deep mine pillars, in this study, presandstone samples are subjected to a controlled high-humidity environment in a custom-built simulation apparatus for 180 days. Humidity levels are meticulously set at 70%, 80%, 90%, and 100% relative humidity (RH) to delineate their effects on the specimens. The specimens are exposed to four predetermined humidity levels (70%, 80%, 90%, and 100% RH) and subsequently undergo uniaxial compression strength and creep testing. A constitutive model to assess rock creep damage, incorporating the interactive effects of humidity and stress, is developed based on the established Burgers model. Utilizing scanning electron microscopy and X-ray diffraction analysis, the study examines the impact of high humidity on the damage mechanisms of mechanical properties through microstructural and mineralogical alterations. The findings reveal that (1) under varying humidity conditions, relative to a 70% RH baseline, specimens in a 100% RH environment exhibited a 27.59% reduction in peak strength, a 43.53% decrease in elastic modulus, and an 11.43% increase in Poisson's ratio. (2) The humidity environment significantly influences the creep properties of sandstone, with increasing humidity levels linearly enhancing the initial instantaneous elastic strain of the material. (3) The integration of a viscoelastic component into the creep constitutive equation for rock masses in high-humidity environments compensates for the traditional Burgers model's lack of detail in describing the accelerated creep stage. The theoretical results of the model have a high degree of agreement with the test results and can more accurately reflect the entire process of rock mass creep. (4) Under high-humidity conditions, sandstone undergoes chemical reactions, including dissolution and hydrolysis, which diminish interparticle friction and consequently lead to irreversible damage to the mechanical properties of the rock.