Mechanical properties of limestone from Maixi tunnel under hydro-mechanical coupling

Abstract

The hydro-mechanical coupling often leads to both mechanical properties and stability deterioration during excavation of water-rich tunnel rock mass. Deformation and mechanical, fracture, and strain energy characteristics of limestone from Maixi tunnel in Guiyang (China) are investigated by hydro-mechanical coupling tests in this paper. Results show that the water pressure has a significant influence on the stress-strain curve, strength characteristics, and macro-fracture degree. The compaction stage is relatively prolonged and elastic phase is shortened. With increasing water pressure, average peak strength decreases exponentially and both average elastic modulus and deformation modulus decrease linearly. The larger the water pressure, the better the fragment uniformity, and fragment uniformity increases exponentially but decreases logarithmically with peak strength. Mercury-injection curve shows a rapid increase then develops gently; the pore volume per unit mass increases exponentially revealing that water pressure has a significant effect on the dissolution pores. Strain energy dissipation characteristics show that total strain energy, dissipation strain energy, and releasable strain energy decrease exponentially with increasing water pressure. Energy ratio Ud/Ut experiences a slow increase, then dramatic rise, and finally develops gently, but Ue/Ut goes through a negative development tend and its boundary points of water pressure are both 2 MPa and 4 MPa. Ud/Ut has a typical logistic function with water pressure reflecting the damage degree and sensitivity of dissipation strain energy to water pressure.