TBM Tunneling Problems through Subterranean Rivers: An Evaluation of Nowsud Tunnel in the Iran (original) (raw)

2022, Research Square (Research Square)

Fault induced subterranean rivers create a major challenge of tunnel construction. They arises serious problems such as TBM performance, structural stability of segmental rings, destruction of TBM components, large water in ow and regional drawdown. Since, the faulted cavity is one of the infrequent adverse geological conditions, not much executive experience has been provided. The TBM of Nowsud tunnel encountered the fault cavities in three places wherein groundwater inrushes from 4.0 to 0.36 m3/s and delayed for 8 months. In each cavity, the main items such as prospecting methods, water inrush and drawdown, type of TBM damages, TBM performance, managing of TBM advance in relation to water discharge, estimation of rockfall impact force and method of segments strengthening were considered. It is found that the fault cavities create in extension part of strike slip faults. In large faults, the TBM could encounter with accessory cavities which hydraulically interconnected to main cavity. Based on gained experiences, TBM excavation along with probe drillings, TSP and appraisal of water discharge, eliminates the hazard of adverse condition. The TBM submerging and damage of other equipment occurs in short term transient part of ow regime while the need to run and capacity of the pumping system are controlled by steady state part. Since, the most of active and passive forces, acting on the TBM, were absent, the re-advancement carried out by quasi-single mode. In this case, the excessive pressures cause the damage stepping of segmental rings. The rockfall impact load was calculated by analytical and numerical methods.