Design equation for stability of shallow unlined circular tunnels in Hoek-Brown rock masses
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ORIGINAL PAPER
Design equation for stability of shallow unlined circular tunnels in Hoek-Brown rock masses Suraparb Keawsawasvong 1 & Boonchai Ukritchon 2,3 Received: 23 August 2019 / Accepted: 8 April 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Safety assessment is one critical issue for constructions of tunnels and requires a reliable and accurate stability analysis. At present, a large number of researches in stability analyses of tunneling in rock masses have been conducted; however, a lack of an accurate and reliable design equation for the tunnel stability prediction is obvious. This paper presents a new design equation for stability analyses of shallow unlined circular tunnels in rock masses obeying the Generalized Hoek-Brown failure criterion. Because of the complexity of the problem’s nature, a closed-formed analytical solution of the problem is not possible to be achieved. Hence, the computational framework of the finite element limit analysis is selected to numerically derive the upper and lower bound solutions of the problem. A complete set of the dimensionless parameters covering the shallow cover-depth ratios of tunnels, the normalized uniaxial compressive strength of intact rocks, and the Hoek-Brown material parameters are comprehensively investigated. A new design equation for stability analyses of shallow unlined circular tunnels in rock masses is developed by employing a nonlinear regression analysis to the numerically derived average bound solutions. It is found that the proposed new design equation is highly accurate and provides a convenient and reliable tool for stability analyses of shallow unlined tunnels in rock masses in practice. Keywords Circular tunnels . Rock mass . Hoek-Brown . Finite element limit analysis . Design equation
List of notations σ1 the effective major principal stress σ3 the effective minor principal stress σci the uniaxial compressive strength of intact rocks GSI the Geological Strength Index of rocks mi the frictional strength of intact rocks
* Boonchai Ukritchon [email protected] Suraparb Keawsawasvong [email protected] 1
Department of Civil Engineering, Thammasat School of Engineering, Thammasat University, Pathumthani 12120, Thailand
2
Centre of Excellence in Geotechnical and Geoenvironmental Engineering, Department of Civil Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand
3
Center of Excellence on Earthquake Engineering and Vibration, Department of Civil Engineering, Faculty of Engineering, Chulalongkorn University, Bangkok 10330, Thailand
DF
the disturbance factor reflected by blast damage and stress relaxation D the diameter of circular tunnels C the cover depth of circular tunnels γ the constant unit weight of rocks σs a uniform surcharge applied over the top rock surface σs/σci the normalized collapse surcharge σci/γD the normalized uniaxial compressive strength C/D the cover depth ratio of circular tunnels q the constant vertical pressure applied on the top plane of plane st
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