What factors influence the selection of disc cutter spacing on a hard rock TBM cutterhead?

Several factors influence disc cutter spacing on a hard rock TBM cutterhead, all aimed at optimizing rock fragmentation, cutter life, and TBM advance rate. Rock type and its properties are paramount. Stronger, more brittle rocks typically require closer cutter spacing to effectively fracture the rock between the cutter paths. Softer, more ductile rocks can tolerate wider spacing. The uniaxial compressive strength (UCS) and tensile strength of the rock are key parameters. The fracture frequency, which describes how many natural cracks exist in the rock, also affects spacing; highly fractured rock may require closer spacing to avoid large, unstable blocks from breaking off. Cutter size and type play a role. Larger diameter cutters generally allow for wider spacing. The desired penetration rate also influences spacing. A higher penetration rate often necessitates closer spacing to ensure efficient rock fragmentation. The cutterhead's geometry impacts spacing selection, including cutterhead diameter and the number of cutters. The goal is to achieve optimal rock fracturing while minimizing cutter wear and maximizing advance rate. Insufficient spacing leads to inefficient rock breakage and higher cutter wear, while excessive spacing results in larger rock fragments that are difficult to handle and can damage the TBM. The 'cutterhead' is the rotating front part of the TBM fitted with disc cutters. 'Disc cutters' are hardened steel wheels that roll across the rock face, applying high pressure to create fractures. The 'uniaxial compressive strength (UCS)' measures the maximum compressive stress a material can withstand before failing. 'Penetration rate' is the distance the TBM advances into the rock per unit of time.