DISTINCT ELEMENT MODELLING OF AN UNDERGROUND OPENING IN JOINTED ROCK MASS

Abstract

The assessment of the stresses and closure around an underground opening are the most important aspects in designing the underground structures. The factors influencing stresses and closure around an underground opening in general may include, the initial in situ stress state, the mechanical properties of the rock mass, the type and properties of tunnel support and the method and the procedure of excavation. Distinct element method is one of the numerical methods which are applicable for continuum as well discontinuum approach and hence is used for analysis in this work. This dissertation presents a parametric study in which the effect of variation of the joint orientation, joint friction angle, and joint spacing on the shear zone, open zone, and closure around an underground opening is studied and analyzed with the help of Universal Distinct Element Code (UDEC). In addition to this, the effect of boundary truncation, stress ratio, and the ratio of model size to opening size is also studied. The study suggests that (i) the ratio of UDEC model size to the opening size may be kept in between 5 to 6 to optimize the results, (ii) a displacement boundary causes both stresses and displacements to be underestimated while a stress boundary does the opposite, and (iii) a 60° joint orientation with joint friction angle 35° is the weakest plane around an opening as compared to 45°, 75°, and 90° joint orientation.