Experimental study on deformation, peak strength and crack damage behavior of hollow sandstone under conventional triaxial compression

• Conduct a series of triaxial experiments for hollow sandstone with various hole diameters
• Analyze the effect of hole diameter and σ3 on deformation parameters of hollow sandstone
• Compare two methods to confirm the elastic modulus and Poisson's ratio of hollow sandstone
• Investigate the effect of hole diameter and σ3 on peak strength of hollow sandstone
• Discuss the effect of hole diameter and σ3 on crack damage threshold of hollow sandstone

Based on a series of triaxial compression experiments using hollow sandstone specimens with various hole diameters (d = 0, 11, 15 and 26 mm), the deformation, peak strength and crack damage behavior of hollow sandstone specimens under different confining pressures are investigated. The experimental results show that the Young's modulus of hollow sandstone only depends on the confining pressure and is not affected by hole diameter in the tested range of d = 0–26 mm. Two types of methods used to confirm the elastic modulus and Poisson's ratio of rock material are proposed to evaluate the triaxial deformation characteristics of hollow sandstone. The effects of confining pressure and hole diameter on the Poisson's ratio and peak strain of hollow sandstone are analyzed. The peak strength and crack damage parameters of hollow sandstone depend on not only the confining pressure (σ3) but also the hole diameter. Under uniaxial compression, the peak strength and crack damage threshold (σcd) of hollow sandstone are independent of hole diameter, whereas the triaxial compressive strength of hollow sandstone decreases linearly with increasing hole diameter. The peak strength and crack damage threshold of hollow sandstone increase with increasing confining pressure, which can be better described by the nonlinear Hoek-Brown criterion than by the linear Mohr-Coulomb criterion. Furthermore, the sensitivity of the crack damage threshold of hollow sandstone to hole diameter is lower than that of peak strength on hole diameter. The concluding remarks can be used to improve the stability and safety of deep underground engineering.