Application of numerical back analysis for determination of soil mass specifications during tunnel construction
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ORIGINAL PAPER
Application of numerical back analysis for determination of soil mass specifications during tunnel construction Motahare Mahmoudi 1 & Ali M. Rajabi 2 Received: 15 October 2019 / Accepted: 2 September 2020 # Saudi Society for Geosciences 2020
Abstract Geotechnical parameters play key roles in constructing and developing civil engineering projects, especially underground structures. One of the conventional methods to evaluate the tunnels’ behavior and safety is applying a back-analysis method to assess the displacement amount during the construction of different parts of the tunnel. Applying this method and using displacement values obtained by tunnel monitoring, the estimated values of geotechnical parameters may converge to their real values. The present study was conducted to improve the estimation accuracy of geotechnical parameters for the tunnel route of Karaj (located 36 km west of Tehran, Iran) subway using the alternative univariate back analysis in FLAC3D software and modifying tunnel maintenance requirements, accordingly. The results showed that the use of geotechnical parameters extracted using back analysis lead to a more accurate design of the tunnel. Overall, through the applied back analysis, it is possible to reduce the shotcrete thickness of some subway stations up to 43% and obtain an optimum design. Keywords Back analysis . FLAC3D . Tunnel . Karaj
Introduction The construction of tunnels in the underground environment made a lot of hazards including land subsidence (Kim et al. 2006; Cheng et al. 2019), flooding (Lyu et al. 2019; Xu et al. 2018), quicksand (Huang et al. 2015), etc. Geotechnical parameters play several critical roles in the stability of soil and rock environments, especially in underground constructions. Among several methods available to evaluate these parameters, back analysis is one of the state-of-the-art techniques used in different under-construction structures. Back analysis is an indirect method applied to estimate the geotechnical parameters of the soil and rock (Tian et al. 2016). The use of geotechnical parameters with low accuracy in constructing
Responsible Editor: Zeynal Abiddin Erguler * Ali M. Rajabi [email protected] Motahare Mahmoudi [email protected] 1
Department of Civil Engineering, University of Qom, Qom, Iran
2
Engineering Geology Department, School of Geology, College of Science, University of Tehran, Tehran, Iran
geotechnical structures, especially tunnels, not only leads to an increase in life loss but also raises the costs of operation. Therefore, it is necessary to apply accurate values of the parameters in designing the structures. During the construction of the tunnel, displacements occur in some parts due to unloading caused by drilling. Such displacements are measured by several methods (Liu and Wei 2018; Luo et al. 2018; Zheng et al. 2018). The combination of back analysis and field surveys results in a reasonable interpretation of tunnel safety assessment, validation, and modification of the primary design of the tunnel
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