Radial opening ratio of EPB TBM cutterheads

The opening ratio of cutterheads, the area ratio of the cutterhead openings to the entire cutterhead, is an important index for selection of earth pressure balanced (EPB) TBM. However, the opening ratio of cutterheads alone cannot fully reflect whether the positions of the cutterhead openings are reasonable or not. To solve this problem, the concept of radial opening ratio of cutterheads is proposed. Based on the characteristic curve of the radial opening ratio, the radial abrasion events of TBM cutterheads during construction of Military Museum Station to East Diaoyutai Station of Beijing Metro Line 9 are analyzed. The main reason of radial abrasion is that the radial opening ratio is too small in a certain area on the cutterhead, and part of the soil deposits in this area. Besides, it also causes the cutterhead to abrase when soil flows from the small opening ratio area to the large one. The characteristic curve of the radial opening ratio can be used to evaluate the rationality of opening position on the cutterhead. For the TBM cutterhead with reasonable opening positions, the characteristic curve of the radial opening ratio should be gentle without large fluctuations except for the central area of the cutterhead so as to ensure the reasonable opening positions in each part of the cutterhead and smooth soil moving into the chamber. The radial opening ratio should be fully considered when designing TBM cutterheads.