Publication Date: 2026
Geotechnical and Geological Engineering (09603182)44(1)
The main bearings of tunnel boring machines (TBMs) are crucial components, typically designed to operate reliably for around 15,000 h under optimal conditions. However, the main bearing of an EPB-type TBM used to excavate Lots 1 and 2 of the 18 km Ghomroud water transfer tunnel in Iran failed after operating for less than 5000 h.This failure happened after only 9 km of excavation and caused serious damage to the TBM main drive system. To identify the cause of this failure, the relationship between the rock characteristics and the TBM’s main drive system was examined.Petrological studies were carried out on rock specimens, including microscopic analysis of thin sections and geochemical analyses using X-Ray Fluorescence (XRF) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). At the same time, lubricating oil from the TBM main drive system was tested with Rotating Disc Electrode Atomic Emission Spectrometry (RDE-AES) and Crackle experiments. The findings indicate that the failure of the TBM seals allowed rock-forming minerals, such as quartz, garnet, feldspar, biotite, chlorite, muscovite, and graphite, along with underground water, to enter the main drive system. The impact of these geological factors is linked to the mineralogical properties and the petrological history of the parent rocks. The results indicate that these geological factors initiate a destructive cycle involving surface scratching, localized loading, deformation, fatigue, and ultimately, failure of the main drive system components. © The Author(s), under exclusive licence to Springer Nature Switzerland AG 2025.
