In this paper, the author discusses the problems encountered in modeling jointed rock reinforced by support structures such as rock bolts. It is well known that rock bolts are extremely effective for reinforcing jointed rock, particularly jointed hard rock. If the concerned rock is highly jointed, a continuum approach could be well applicable in its modeling. It should be noted, however, that in a continuum approach, mechanical properties such as Young's modulus and shear strength are properties for a continuous material mechanically equivalent to the jointed rock. Therefore, if rock bolts are installed for reinforcing equivalent material, the effect of the rock bolts in restricting the movement of the joints is not properly taken into account because all the joints have disappeared. In order to overcome this difficulty, jointed rock should not be modeled independently of the rock bolts, but should be modeled simultaneously by considering the effect of the rock bolts. For determining the mechanical parameters of equivalent material, the homogenization theory is applicable at the design stage, and a back analysis technique can be used during the excavation.
Numerical analysis is a powerful tool when designing rock structures like tunnels and slopes. However, the accuracy of numerical analyses entirely depends on what numerical model is used to model the rock. Since there are various uncertainties involved in the geological and the geomechanical characteristics of rock, it is not an easy task to model the rock.
In the modeling of rock, there are two approaches available. One is a continuum approach and the other is a discontinuum approach. If a rock mass is highly jointed, the continuum approach could be well applicable. In the continuum approach, it should be noted that the values for the mechanical properties, such as Young's modulus and shear strength, determined by in situ tests such as plate bearing tests and direct shear tests, respectively, are values for a continuous material mechanically equivalent to the jointed rock mass. In other words, the concerned jointed rock mass is implicitly assumed to be a continuum from which all joints disappear.
Therefore, it is obvious from Fig. 1 that if rock bolts are installed into such an equivalent material, the effect of the rock bolts in restricting the movement of the joints may not be properly taken into account. This means that in the continuum approach, the effect of restricting the movement of the joints should be taken into account in a suitable manner.
(Figure in full paper)
Fig. 1 Conventional continuum approach for the modeling procedure for a jointed rock mass reinforced by rock bolts
The Hoek-Brown criterion is one of the most popular failure criteria for rock masses. The criterion is given in the following equations:
(Equation in full paper)