Experimental study of deformation and strength properties of simulated columnar jointed rock masses under conventional triaxial compression

The columnar jointed rock mass is a common kind of structure rock mass in extrusive igneous rocks, and correct understanding the deformation and strength characteristics of columnar jointed rock mass under triaxial stress condition was one of the key problems that should be solved for the demonstration and design of large scale rock mass projects such as hydropower station and underground cavern excavations. Therefore, in this paper, plaster mixture was used to prepare simulated columnar jointed rock mass specimens with different dip angles β between the direction of maximum principal stress σ1 and column prisms. Conventional triaxial compression tests with different confining pressures are carried out on these specimens and the variations of Young's modulus and peak compression strength with dip angle β are obtained. From the experimental results, it is found that for seven groups of specimens under the same confining pressure, the curves of Young's modulus and peak strength vs. dip angle β resemble as decreasing order-shaped, that is, the Young's modulus and peak strength decrease with dip angle β from 0° to 45° and the minimum values of Young's modulus and peak strength occur at β = 45°, then the Young's modulus and peak strength remain relatively constant with the increase of dip angle. Furthermore, based on the experimental results, an empirical expression is proposed to predict the Young's modulus and peak strength of columnar jointed rock mass specimens. It is found that the empirical expression can well predict the changes of Young's modulus and peak strength with dip angle β by comparing the theoretical curve with experimental data. Additionally, four types of typical failure modes of columnar jointed rock mass under triaxial compression condition are summarized based on test results and the failure mechanisms are also discussed. ©, 2015, Academia Sinica. All right reserved.