Mechanical behaviors and wetting-induced deformation of metamorphic granite based on large-scale triaxial test

The surrounding rock mass of underground engineering containing abundant groundwater in fault fracture zones is weak and broken, and is susceptible to severe collapse caused by humidification, thus resulting in many technical problems for engineering maintenance. Taking metamorphic granite of the fault fracture zone at Wuyue Pumped Storage Power Station, Henan province of China, as the object, large-scale tri-axial tests were conducted to investigate the mechanical behavior and wetting-induced deformation of rock masses under the hydraulic environment including moisture content, confining pressure and stress level. The test results reveal that, as the confining pressure increase, the peak strength and peak strain of specimens increase under different water states, and that the peak strength under dry state is respectively 22.90% and 27.33% averagely higher than that under natural and saturated states while the difference between the latter two is only 3.61%. It is worthwhile mentioned that the peak strain is the largest under natural state and the smallest under dry state, indicating that the peak strain is markedly influenced by the moisture content. It is also shown that the wetting-induced strain increment (i.e. axial strain increment -△ε1s, volume strain increment -Δεvs and shear strain increment Δγs) is significantly affected by the stress level and confining pressure, and that effect the stress level on these three indicators is more sensitive compared to the confining pressure. In particular, 1 time increment of the stress level will lead to the improvement of the three indicators by an average of 2.59, 1.41 and 3.17 times, respectively. Comparison of the strength and deformation of granite samples before and after wetting shows that wetting deformation not only weakens the strength properties of the rock mass but also increases the volumetric deformation. The proposed calculation model upon wetting-induced deformation obtained through the experimental results was recommended as the reference for safety assessment of wetting-induced deformation of surrounding rock masses and the numerical analysis. © 2020, Science Press. All right reserved.