Failure wear mechanism and blade width effect of TBM center cutter rotation in water-bearing weakly cemented sandstone.

Weakly cemented sandstone (WCS) in western China is rich in clay minerals. Water‑induced softening tends to induce rotation failure of TBM central hobs, which further causes eccentric tip damage and edge chipping and remarkably reduces tunnelling efficiency. Aiming at the poorly understood sliding‑contact mechanism of central hobs under rotation‑failure conditions in WCS strata, steel‑needle scratching tests combined with XRD and SEM micro‑characterization were carried out to investigate the apparent morphological evolution of hob tips, and a corresponding empirical correlation was fitted. The results show that water saturation may promote softening of clay cement, trigger the generation of rock slag and give rise to secondary interfacial abrasion. Measured data from WCS scratching tests indicate that the relative apparent‑diameter variation of the 0.4 mm needle for water‑saturated specimens is 1.53 times that of the 1.0 mm needle, and the geometric variation of the 0.4 mm needle increases by 45%‑57% compared with dry conditions. With correction terms of equivalent blade width and water content incorporated, the empirical correlation reproduces tip‑morphology variation trends that are generally consistent with field observations of domestic TBM projects. Based on scaled steel‑needle tests, this study reveals the corresponding evolution law of tip‑contact responses for TBM central hobs under rotation‑failure conditions in Cretaceous WCS strata, and can provide experimental basis and theoretical references for hob structural design, cutter‑head layout and tunnelling‑parameter optimization for such strata. This mechanistic analysis relies on quasi‑static scratching tests and focuses on sliding‑contact behaviours at the tool‑rock interface. Its engineering application should be comprehensively evaluated combined with in‑situ dynamic tunnelling conditions.