PhD, CEng, MICEB. Jones, University of SouthamptonThe surface settlement points were between 11 .09 m and12 .47 m above the frontshunt tunnel axis level duringconstruction, not 14 .8 m as stated by the authors. Above thetunnel centreline, the settlement points varied from 11 .26 mabove the tunnel axis level at Array 1 to 12 .31 m above thetunnel axis level at Array 6. About a year after frontshuntconstruction ceased, the ground was made up to a level ofapproximately 14 .8 m above the tunnel axis level, and this isprobably where this number came from. The analysis presentedtherefore overestimates the depth of the tunnel by more than2 m at least, and in some areas by almost 4 m.The overall advance rate during construction of the frontshunttunnel was 1 .4 m/day, but while crossing the so-called 2Dzone marked in Fig. 3 it was 1 .7 m/day. If a weekend break inthe middle of this zone at a chainage of 30 .3 m were ignored,the average advance rate would have been 2 .5 m/day acrossthis zone.In Section 4 .1, paragraph 3, the authors state: ...there is a0.5 m overhang left from the previous cycle initially supportedwith 75 mm of shotcrete that must be broken out. The purposeof the overlap was to stagger the joints of the initial layer andprimary lining and thereby improve durability and waterresistance. Breaking out of the overlap of the initial layer wasof course not done on site.Figures 10 and 11, which show the ground displacements fromthe numerical modelling at the surface and in the ground,cannot be reconciled. Although the contours and vectors inFig. 11 do not extend to the surface, scaling off the gureshows that the upper limit of the contours and vectors is at13 .3 m above the tunnel axis, that is, 1 .5 m below the groundsurface in the model. It is dif cult to see how the computedsettlement above the centreline at 1 .5 m depth can be 25 mm inFig. 11, while Fig. 10 shows that the computed settlement atthe surface was only 9 .5 mm.Section 4.3 states: The use of SCL to provide a rapid stiffsupport, minimising ground movements, would be inaccordance with SCL design philosophy, where the lining isdesigned to accommodate high loads while minimisingdisplacements.