Abstract
The construction of tunnel portals in mountainous or slope areas often involves problems, which are closely related to factors, such as slope topography, geology, geotechnics, construction geometry and the tunnel excavation method. The activation of landslides or the acceleration of these events is one of the main challenges faced in the construction of tunnel portals. In this paper, we address the instability problem in Sabzkuh tunnel portal that has been excavated with a complex geological profile and high seismicity in Iran’s High Zagros region. The complexity and intense heterogeneity in geological formations, land acquisition problems and the lack of appropriate monitoring programs led to the instability of the tunnel portal. The excavation process started without applying appropriate techniques for a ground stabilization. The use of inappropriate tunnel excavation methods for this unstable geological structure resulted in an activation of an old Solaghan fault and several collapses in the tunnel. Crossing the collapsed areas and reinforcing the tunnel portal took about 7 months and imposed heavy costs on the project. This case study deals with the importance of the choice of the site location, ground and underground monitoring, analysing and summarizing the collected data in order to prepare a geological model before and during the construction process.
Highlights
Sabzkuh water conveyance tunnel with a length of 10,617 meters is being excavated using both conventional and mechanized techniques in Chaharmahal and Bakhtiari Province across the Iran’s central zone and Zagros and with a close distance from the Zagros Fault in the High Zagros region
This paper presents a case study of the instability at Sabzkuh tunnel portal, which is located in an area with a high potential for landslides, faults and the complex geological structures that were not known before starting the tunnelling operations
This article presents a case study of the activation of a landslide resulting from the tunnel excavation in an area with complex geological conditions and active tectonics that were not identified before starting the tunnelling operation
Summary
Sabzkuh water conveyance tunnel with a length of 10,617 meters is being excavated using both conventional and mechanized techniques in Chaharmahal and Bakhtiari Province across the Iran’s central zone and Zagros and with a close distance from the Zagros Fault in the High Zagros region. High groundwater levels in the region, and the inability of the project employer to acquire enough land to build the tunnel entrance in an appropriate location, the slope stability in the Sabzkuh tunnel entrance faced a challenge. After constructing tranches and before starting the tunnel excavation, signs of slope instability were observed As these signs were not taken seriously and there were no proper monitoring programs as well as guidelines and appropriate measures for stabilization, the instability level was intensified. This paper presents a case study of the instability at Sabzkuh tunnel portal, which is located in an area with a high potential for landslides, faults and the complex geological structures that were not known before starting the tunnelling operations. The collected data were accumulated in a database in order to analyse the landslide profile, find slope improvement strategies, and continue the excavation operation
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