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Lookup NU author(s): Professor Stefano Utili
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A systematic approach of using the distinctelement method (DEM) to provide useful insights fortunnel support in moderately jointed rock masses is illustrated.This is preceded by a systematic study of commonfailure patterns for unsupported openings in a rock massintersected by three independent sets of joints. The resultsof our simulations show that a qualitative description of thefailure patterns using specific descriptors is unattainable.Then, it is shown that DEM analyses can be employed inthe preliminary design phase of tunnel supports to determinethe main parameters of a support consisting of rockbolts or one lining or a combination of both. A comprehensiveparametric analysis investigating the effect of boltbonded length, bolt spacing, bolt length, bolt pretension,bolt stiffness and lining thickness on the tunnel convergenceis illustrated. The highlight of the proposed approachof preliminary support design is the use of a rock bolt andlining interaction diagram to evaluate the relative effectivenessof rock bolts and lining thickness in the design ofthe tunnel support. The concept of interaction diagram canbe used to assist the engineer in making preliminary designdecisions given a target maximum allowable convergence.In addition, DEM simulations were validated againstavailable elastic solutions. To the authors’ knowledge, thisis the first verification of DEM calculations for supportedopenings against elastic solutions. The methodologiespresented in this article are illustrated through 2-D planestrain analyses for the preliminary design stage. Morerigorous analyses incorporating 3-D effects have not beenattempted in this article because the longitudinal displacementprofile is highly sensitive to the joint orientationswith respect to the tunnel axis, and cannot beestablished accurately in 2-D. The methodologies andconcepts discussed in this article, however, have thepotential to be extended to 3-D analyses.
Author(s): Boon CW, Houlsby GT, Utili S
Publication type: Article
Publication status: Published
Journal: Rock Mechanics and Rock Engineering
Print publication date: 01/03/2015
Online publication date: 13/04/2014
Acceptance date: 18/03/2014
ISSN (print): 0723-2632
ISSN (electronic): 1434-453X
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