Undrained Stability of Dual Circular Tunnels

In this paper,numericallimit analysis and semianalytical rigid blocktechniques are used toinvestigate the effectof the tunnelspac- ingonthestabilityoftwocirculartunnelsexcavatedsidebyside.Thetunnelsaremodeledunderplane-strainconditions,whichimpliesthatthey are assumed to be infinitely long. Bounds on the stability of the tunnels are obtained using finite-element limit analysis, the numerical formu- lation of which is based on the upper and lower bounds theorems of classical plasticity. Solutions are obtained using advanced conic program- mingschemes tosolvethe resultingoptimization problems,and upperand lowerboundestimates on thestabilityof thetunnels areobtained for arangeofgeometries.Thesebounds,whichbracketthetruecollapseloadfromaboveandbelow,arefoundtodifferbyatmost5%forthecases where the solution does not approach zero. Results from this study are summarized in stability charts for use by practitioners. DOI: 10.1061/ (ASCE)GM.1943-5622.0000288. © 2014 American Society of Civil Engineers. Author keywords: Tunnels; Stability; Limit analysis; Finite-element method (FEM).

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