Geotechnical Engineering Online Library

Damage smear method (DSM) is adopted to study trans-scale progressive rock failure process, based on statistical meso-damage model and finite element solver. The statistical approach is utilized to reflect the mesoscopic rock heterogeneity. The constitutive law of representative volume element (RVE) is established according to continuum damage mechanics in which double-damage criterion is considered. The damage evolution and accumulation of RVEs are used to reveal the macroscopic rock failure characteristics. Each single RVE will be represented by one unique element. The initiation, propagation and coalescence of meso-to macro-cracks are captured by smearing failed elements. The above ideas are formulated into the framework of the DSM and programed into self-developed rock failure process analysis (RFPA) software. Two laboratory-scale examples are conducted and the well-known engineering-scale tests, i.e. Atomic Energy of Canada Limited's (AECL's) Underground Research Laboratory (URL) tests, are used for verification. It shows that the simulation results match with other experimental results and field observations.

Deep drilling is becoming the direct and the most efficient means in exploiting deep mineral resources, facilitating to understanding the earthquake mechanism and performing other scientific researches on the Earth's crust. In order to understand the limit of drilling depth in the Earth's crust, we first conducted tests on granite samples with respect to the borehole deformation and stability under high temperature and high pressure using the triaxial servo-controlled rock testing system. Then the critical temperature-pressure coupling conditions that result in borehole instability are derived. Finally, based on the testing results obtained and the requirements for the threshold values of borehole deformations during deep drilling, the limit of drilling depth in the Earth's crust is formulated with ground temperature.