Selection of TBM and geotechnical assessment of a microtunnel in a difficult geological environment: a case of a natural gas pipeline beneath an active landslide (Albania)

Abstract

This present paper presents an adopted methodology for Micro Tunnel Boring Machine (TBM) selection, based on the results of a geological-geotechnical feasibility assessment of a microtunnel, planned for a natural gas pipeline beneath an active landslide, in the Corovode area, southern Albania. This example offers an excellent case study of diverse and demanding engineering geological formations, namely disturbed and sheared types of flysch rock masses, but also recent soil deposits. A tunnel drive will confront materials that may be prone to posing challenges, such as ravelling ground at the microtunnel face, chimney failures, water inflows, as well as deformations. The selection of the appropriate tunnelling method procedure is analysed and presented step by step, addressing all issues that cover the most critical aspects of the selection process. Finally, a geotechnical feasibility assessment is presented as an overall analysis of this work, taking into consideration all the crucial design parameters for several Micro TBM types along the tunnel. Besides the expected rock mass behaviour, the TBM selection is also based on the percentage of fines at the tunnel excavation profile, the permeability and hydraulic head, which is also investigated in this study, while sticky behaviour, clogging risk, presence of obstacles and mixed ground conditions are also taken into account.