Positioning the Peripheral Cutters in Hard Rock TBMs

One of the most important goals in the design process of the TBMs is to determine the proper positions of the peripheral cutters. Since the actual penetration of the peripheral cutters in the tunnel face is lower, the normal force applied by them to the tunnel face is also lower. In order to avoid ridge formation between these cuters and to avoid asymmetric forces applied to the flanks of the cutters, it is necessary to gradually reduce the cutter spacing in the peripheral area of the cutterhead. The design of the peripheral cutters’ parameters (spacing and tilt angle) are usually performed experimentally, and there is no theoretical background for it in the literature. In this paper, an empirical model is introduced to determine the optimum configuration of the peripheral cutters on the cutterhead profile. This model is developed based on the principles of the optimum excavation using the optimum ratio of spacing to penetration rate (S / p), as well as the information of design details of a number of hard rock TBMs from around the world. The results of this model provide the optimum spacing of disc cutters and their corresponding tilt angles and normal forces for the peripheral cutters.