Uniformly distributed lace design for hard rock TBMs

Optimization in TBM cutterhead design is essential for increasing its performance. Lace design for the cutters, buckets, and manholes in the cutterhead, is one of the major considerations in the design of the hard rock TBMs. An optimum lace design is necessary to avoid cutterhead deviation, vibration, and stress concentration during its operation. TBM manufacturers usually utilize two common lace designs of radial and spiral configurations. Despite the presence of many advantages for these two designs, each of them has its own disadvantages which may cause difficulties in achieving an efficient design of the cutterhead. This paper introduces a new TBM cutterhead lace design in which all three normal, side, and rolling forces are considered. The new force and moment balancing relationships are presented. With the consideration of the problems of the radial and spiral configurations, a new method of "uniformly distributed lace design" is introduced and the steps of achieving the final layout of the cutterhead is explained with its required parameters. On the basis of an example, a comparative study is made among three methods of applying radial, spiral, and uniformly distributed lace designs. The results show that the new method is very efficient in both uniformly and symmetrically distributing the cutters, buckets, and manholes on the cutterhead surface with no boundary conflicts. It also has the advantage to have low unbalanced forces and moments.