Experimental study on the triaxial mechanical behaviors of the Cemented Paste Backfill: Effect of curing time, drainage conditions and curing temperature.

The application of CPB (Cemented Paste Backfill) can realize the clean, efficient, and safe mining of underground metal mines. Clear understanding on the triaxial mechanical properties of CPB is important to the CPB design and the stability analysis of the backfilled CPB structure. The triaxial mechanical properties of CPB can be significantly affected by the different curing conditions. In this research, triaxial compression tests of the CPB samples were carried out using the GCTS (Geotechnical Consulting & Testing System), and the considered curing conditions include different curing time (1, 3, 7 and 28 days), drainage conditions (drained and undrained) and curing temperatures (20 °C, 35 °C and 45 °C). The measured mechanical parameters were compared and analyzed against the framework of the Mohr-Coulomb criterion. Then, the vertical stress distribution of the backfilled CPB structure was calculated and discussed using the measured mechanical parameters. The results show that with the increase of the lateral constraint ratio (σ/S), the elastoplastic stage of the measured deviator stress versus axial strain curve of CPB sample is gradually obvious. The peak deviator stress (S) and the ultimate axial strain (ε) show the linear and negative exponential increase with the σ/S respectively. The number of cracks on the fractured surface of the CPB samples gradually decreased with the increase of σ/S. The failure types of CPB samples were changed from tensile failure (σ/S = 0%) to the mixed tensile-shear failure (σ/S≈10%) and compression-shear failure (σ/S≥20%). Moreover, with the increase of curing time and curing temperature or under the drained curing condition, the peak deviator stress and cohesion (c) of CPB can be significantly increased, but the corresponding internal friction angle (ϕ) is decreased. The shear mechanical parameters of CPB can significantly affect the vertical stress distribution inside the CPB structure. Therefore, when estimating the vertical stress distribution inside the backfilled CPB structure in engineering practices, it is necessary to focus on the changes of CPB shear parameters (c and ϕ) caused by different curing conditions.