Robert Bertuzzi

aPells Sullivan Meynink,North Ryde,NSW 2113,Australia

bSchool of Civil and Environmental Engineering,University of New South Wales,Kensington,NSW 2052,Australia

The recent paper by Bertuzzi(2017)published in Journal of Rock Mechanics and Geotechnical Engineering(JRMGE)included the correlation of rock mass deformation modulus,M,with theQ-value as presented in the first part of Barton(1995).This is reproduced here as Eq.(1):

The unconfined compressive strength(UCS)normalisedQ-value,Qc,was introduced in later pages of the article by Barton(1995)to improve the correlation of rock mass quality and seismic velocity.TheQcvalue is obtained by normalising to nominal hard rock compression strength value of 100 MPa as given in Eq.(2):

Publications subsequent to Barton(1995),such as Barton(2002)and Barton and Grimstad(2014),further clarified the use ofQcto improve correlation between rock mass deformation modulus and seismic velocity.Hence,Eq.(1)should be written as:

With regard to the two rock masses of interest in Bertuzzi(2017),the use ofQcinstead ofQ,i.e.Eq.(3)instead of Eq.(1),decreases the predicted range of rock mass modulus for Hawkesbury sandstone from 17-42 GPa to 8-34 GPa and that for Ashfield shale from 11-37 GPa to 5-27 GPa.Fig.6 in Bertuzzi(2017)therefore is modified herein.

The author apologises to Dr.N.Barton for not including theQccorrelation in the original publication of Bertuzzi(2017).

Barton N.The influence of joint properties in modelling jointed rock masses.Keynote.In:Proceedings of the 8th ISRM Congress.A.A.Balkema;1995.p.1023-32.

Barton N.Some new Q-value correlations to assist in site characterization and tunnel design.International Journal of Rock Mechanics and Mining Sciences 2002;39(2):185-216.

Barton N,Grimstad E.Forty years with the Q-system in Norway and abroad.In:Fjellsprengningsteknikk,Bergmekanikk/Geoteknikk.Tapir Trondheim;2014.pp.4.1-25.

Bertuzzi R.Back-analysing rock mass modulus from monitoring data of two tunnels in Sydney,Australia.Journal of Rock Mechanics and Geotechnical Engineering 2017;9(5):877-91.