Assessment of support system for tunnel excavation in highly squeezing fault zone conditions

In tunnel excavations within squeezing rock masses, it is difficult to predict rock behavior due to the plasticity of the surrounding rocks (often of low rock quality and/or under high stress). Therefore, squeezing rock tunneling has always been a challenging problem for tunnel engineers and researchers, leading to the emergence of passive and active support approaches. Both approaches begin by determining the geological conditions and identify the factors and mechanisms that cause damage resulting from excessive deformations, thereby minimizing problems encountered during excavations. This study focuses on the T26 tunnel, which was constructed under complex geological conditions, subject to severe tectonic influences, and in extremely weak rock masses. The purpose is to determine support system procedures for excavating the reverse fault zone area following the tunnel by utilizing damage data resulting from excessive deformation of the rock mass. This support system procedure primarily involves a series of temporary supports used to ensure tunnel face stability during tunnel excavation. This involves the initial lining, which allows for very low deformations (passive support), followed by the final lining, which is reinforced with steel (active support), while deformations continue, albeit minimally, and do not exceed a certain level. The results of this case study demonstrate that a safe and efficient construction process in extremely weak and squeezing rock mass in a severe tectonic environment requires first ensuring tunnel face stability. Furthermore, the proposed support system, which combines active and passive support (rigid) has been determined to be a viable support system in squeezing rock mass. The results obtained from the study may provide information and guidance for tunnel projects under similar conditions.