Influence of Forepoling Umbrella on the Settlements Induced by Shallow Urban Tunneling
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ORIGINAL PAPER
Influence of Forepoling Umbrella on the Settlements Induced by Shallow Urban Tunneling Ali Naghi Dehghan
Received: 4 August 2019 / Accepted: 6 May 2020 Ó Springer Nature Switzerland AG 2020
Abstract In this study, the influence of a forepoling umbrella system to control ground surface settlements induced by shallow tunneling in urban areas under dynamic railway traffic loads was investigated. 2D and 3D numerical models of the Zarbalizadeh-Maddah underpass tunnel were developed to evaluate excavation face stability and ground deformations. The 2D modeling results indicate stable conditions of the tunnel due to its well-designed support systems. Based on a sensitivity analysis performed in the 2D modeling, cohesive strength and elastic modulus of the equivalent element to the forepoling zone, show the greatest effect in controlling ground surface settlement. In spite of the stable condition of the tunnel, surface settlement obtained from the 2D numerical modeling results in a relatively higher value than instrumentation data (around 43%), recorded during tunnel excavation. In order to more accurately investigate the effect of forepoling on surface settlement, a 3D simulation was performed, with consideration of the Longitudinal Deformation Profile of the tunnel face to better estimate stress relief for different stages of excavation. The results displayed a lower value of
A. N. Dehghan (&) Department of Mining Engineering, Faculty of Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran e-mail: [email protected]
surface settlement compared to the 2D model, and in good agreement with the instrumentation data. Therefore, a forepoling pre-support system could have a pivotal role on the control of ground surface settlement by developing the radial and longitudinal arching around the excavated opening of a tunnel in shallow soft ground under high dynamic loading. Keywords Shallow urban tunneling Ground surface settlement Numerical modeling Forepoling umbrella system
1 Introduction Traffic is always on the rise in developing cities and the excavation of tunnels for traffic flow and subway railways is part of this trend. Urban road tunnels are mainly excavated in alluvium media with specific geological conditions. Excavation and tunnel construction in urban areas includes consequent effects and challenges, primarily ground settlement. The effects of settlement due to urban tunnels under construction on above ground structures and urban infrastructure are of paramount significance. Therefore, employing pertinent methods to predict and control ground settlement is the most significant parameter in the design and construction of urban road tunnels to ensure the safety of above ground structures (Fang et al. 2016; Sadeghi et al. 2016).
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Geotech Geol Eng
During the excavation of an underground space or a shallow tunnel in soft ground, changes in the internal stress state of the geological medium lead to deformations in
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