Optimum design of the peripheral cutters’ specification on the head profile for hard-rock TBMs

One of the most important goals in the design of the TBMs is to optimize the arrangement of the peripheral cutters on the cutterhead layout. Peripheral cutters refer to the cutters installed on the curved area near the periphery of the TBM cutterhead. This optimization is essential to improve TBM performance (e.g. penetration rate) and to control the interaction of the cutters (e.g. cutter normal force) with the tunnel face. The actual penetration of the peripheral cutters in the tunnel face is relatively lower which leads to lower applied normal force. To avoid ridge formation between these cutters and to prevent high asymmetric forces applied to the flanks of the cutters, it is necessary to gradually reduce the cutter spacing in the peripheral region of the cutterhead. The evaluation of the design specifications of the peripheral cutters, including spacing, tilt angle, and normal force is typically relying on experience and engineering judgment. To improve such strategies and to achieve an efficient design for the cutterhead lace design, an optimization method is introduced based on the statistical analysis of the cutterhead design details of various TBMs from around the world, as well as the principal of using the optimum ratio of spacing to the cutter contact area (S/Acon). The results of this method provide the optimum spacing of disc cutters and their corresponding tilt angles and normal forces for the peripheral cutters. In developing relationships for the peripheral cutters’ normal forces, graphical methods are utilized to calculate the actual cutter contact area and the actual cutter indentation area for different values of cutter tip width, cutterhead curvature radius, and tilt angle. In this regard, a multivariate regression formula is presented to evaluate the actual indentation area. To illustrate the steps presented in this method, an example is provided and the details of the design procedure and its final results are explained. The results of the proposed method establish a new foundation to improve the design process of hard-rock TBMs to help prevent structural damages and low performance. © 2020 Elsevier Ltd