Verification of a laboratory-based dilation model for in situ conditionsusing continuum models

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Veri?cation of a laboratory-based dilation model for in situ conditions using continuum models

G.Walton a,*,M.S.Diederichs a,L.R.Alejano b,J.Arzúa b

a Queen’s University,Kingston,Canada

b University of Vigo,Vigo,Spain

a r t i c l e i n f o

Article history:

Received25June2014

Received in revised form

18September2014

Accepted26September2014 Available online1November2014

Keywords:

Dilation

Continuum models

Case studies

Brittle rock a b s t r a c t

With respect to constitutive models for continuum modeling applications,the post-yield domain re-mains the area of greatest uncertainty.Recent studies based on laboratory testing have led to the development of a number of models for brittle rock dilation,which account for both the plastic shear strain and con?ning stress dependencies of this phenomenon.Although these models are useful in providing an improved understanding of how dilatancy evolves during a compression test,there has been relatively little work performed examining their validity for modeling brittle rock yield in situ.In this study,different constitutive models for rock dilation are reviewed and then tested,in the context of a number of case studies,using a continuum?nite-difference approach(FLAC).The uncertainty associated with the modeling of brittle fracture localization is addressed,and the overall ability of mobilized dilation models to replicate in situ deformation measurements and yield patterns is evaluated.

ó2014Institute of Rock and Soil Mechanics,Chinese Academy of Sciences.Production and hosting by

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1.Introduction

Recently,numerical methods have become increasingly popular tools to analyze rock mass https://www.wendangku.net/doc/4d15310102.html,puter programs which represent rock masses as continua and discontinua can be used to predict loads and displacements in rock structures and support or reinforcement systems or to verify hypotheses about observed behavior(back analysis).Although these tools are no longer restricted to research applications,models used in the study of civil and mining geotechnical structures are often limited in their complexity(i.e.elastic models for stress prediction).This is largely due to the questions about the validity of more complex models.In fact,the use of inadequate material models is one of the largest limiting factors in numerical analyses(Lade,1993;Carter et al., 2008).

Continuum models are more commonly used than dis-continuum models in rock engineering(even when they are not necessarily appropriate).The existing experience base in the geotechnical community with respect to modeling rock masses as continua is a major driver of this phenomenon(Bobet,2010). Although rapidly evolving discontinuum and hybrid continuum/discontinuum modeling tools provide a valuable alternative to continuum models for some applications(see Jing(2003)and Bobet(2010)),it is important to continue to improve constitutive models for use in continuum models given their relative accessi-bility and ease of use.

One area of particular historical de?ciency in terms of constitutive models for rocks and rock masses is their post-yield volumetric response to continued deformation.Correspondingly, the tendency of rock masses to dilate following yield has been a topic of increased research recently.Understanding this phe-nomenon may be integral in allowing for the accurate prediction of yield and ground movement;this is particularly true of more brittle rocks,which tend to dilate most signi?cantly(Hoek and Brown,1997).

In this study,different approaches for modeling dilative behavior are reviewed,and then used in a back analysis of exten-someter data obtained from the Donkin-Morien Tunnel(Nova Scotia,Canada).One dilation model in particular is then applied to further case studies to illustrate its ability to successfully replicate displacements measured in situ.

2.Models for rock dilation

The tendency of rocks to expand under compression was?rst shown to be a true material property(rather than an in?uence of the testing system)by Cook(1970).Although the underlying mechanisms for this phenomenon are fundamentally brittle(see Brace et al.(1966)and Jaeger and Cook(1969)),different formu-lations based on plasticity theory have been developed over the

*Corresponding author.Tel.:t16138934223.

E-mail address:7ggw@queensu.ca(G.Walton).

Peer review under responsibility of Institute of Rock and Soil Mechanics, Chinese Academy of Sciences.

1674-7755ó2014Institute of Rock and Soil Mechanics,Chinese Academy of Sci-ences.Production and hosting by Elsevier B.V.All rights reserved.

https://www.wendangku.net/doc/4d15310102.html,/10.1016/j.jrmge.2014.09.004

Contents lists available at ScienceDirect Journal of Rock Mechanics and Geotechnical Engineering journal h omepage:ww w.rockgeote

https://www.wendangku.net/doc/4d15310102.html, Journal of Rock Mechanics and Geotechnical Engineering6(2014)522e534