The effect of fracture patterns on penetration rate of TBM in fractured rock mass using probabilistic numerical approach

Existence of discontinuity features has a great influence on mechanical properties and cuttability of a rock mass. In the literature, the influence of geometrical properties of joint sets such as joint spacing and orientation on penetration rate (PR) of a tunnel boring machine (TBM) were investigated and reported. However, the actual fracture pattern in a rock mass is more likely a discrete fracture network. The numerical probabilistic distinct element method (DEM) modeling of PR of a TBM is a very useful method that simulates very complex geometrical models of fracture systems, such as stochastic discrete fracture network (DFN) models with different possible fracture patterns close to the tunnel face. The formed chipping area under TBM cutters are investigated for both intact rock (IR) and DEM models and additional chipping area of fractured models in comparison with IR model are calculated. The probability density function of percentage of additional chipping area follows a normal distribution with mean value of 46 %. Results represent that the additional chipping area of 95 and 80 % of DFN-DEM models are 20 and 33 %, respectively, which shows that numerical modeling of PR of a TBM based on an intact rock is underestimated about 20 and 33 %. Fracture pattern also controls the formed chipping area under each cutter.