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' BRIDGE VERSUS TUBE.
TO THE EIUTOll.
Sir- "Welaiid Trulpigh Broke, CE., in h|3 letter on the above question, has furnished me vyth tîje infoimptiop I have been looking for, vu.:-As to how ths csliinates h-ivo been worked out for the
construction of a tube pcios» the Brisbane llivei, apd this has led somo people to look upon it as a vcrv expensive under tal ing The Holland Tunnel under the Hudson River at New Yoil we me told is OOoOft in length fiom poital to portal
and is estimated to cogt £884 per lineal foot and this notwithstanding that its enoimous length and the difficulties of driving that have been oncouutered is taken as a basis for estimating the cost of tho comparatively easy proposition wo have to faco I will take the figures before mo to prove how misleading it is to estimate »oik on thoso lines Taking the depth us stated in the letter at 74ft to the lowei (ondwny 1 in 20 fvpproacli in tlie direction pf liveyyays Geotge strpet and 1 dwurdslioct yvoiild be l^Sflft io spectively, mai mr a total of 4140ft for nppinaçhe1- as u-amst the (¡Q8()ft given m the letlei Ave can theipfpie, take off for a start )200ft at £SSi pm foot
This we nil take from the (»tímate £1 060 8Q0 toi the woil leading up to the ar-pioaches of 1 in 20 woik which could be cnnied out ly the council nt oidtnaiy load mai me, prices lu tbp foimntion of oin api ioichcs We begin to descend "3ft foi even 00 linee roads will give us 180ft rr accenting to the estimate 1C0120 Uns woil oouhl ensih lie rained out for £0120 biinglng down the estimate bv nnolliei £la0 000 Ho fir e have dispose 1 of £1210 800 let us take another fOft of formation nt each of the nppioichce which would mean au excava tion Oft deep the extia cost of which would bo £17ri0 over tho cost of tho fiist 00ft-oi £12 870
I stimnted copt £159 120 minus f-12 870 pi anptliei saving of £116 2,i0 So fa- ne |iave biouglit the estimite down by filislOoQ md baye oply scintched the surface I do not think it is ppcpssarv to go nitp any inore fignirs of tbis 1 ind I hoip been a student of civil ongmeeiing for ovei 25 veaii- have piepned plans mid ciriied out a higo amount of con structional worl elurnir, that period and I believe in. eslipiating for the wo k in the location in which it )s to be carried out whelp the supplies of material and the methods nocessaiy foi ceonomj must always lnvo a bealing on the coils If the woil were cnnied out on the lines I have indicated (building the tube above water instead of dnving) it yvould effect n saying mi the suhmeigcd part of the tube (1200ft) of soinethine. like CnQOOOO working on tho Hudson Tunnel basis of £881 ppt foot If we aie asked to be 1 eve that a lube is more costly than a h gh level bn]v,e why do the Qnginceis of the Bivpr Mer ey tube chun a saving of £4 320(100 pvpi Hie cost of a high level brult-e nud m riiUitinn much easier Piadients' AMiv did the Citv of London (lecjdp to cniistiuct apolhei tulip under the Thames' \nv one who has dnvep thiough the Bhcl vv all luniiel with ltr white tiled walls would at once sai
lins is the liest solution of oin cross
1 rhpi difficulties "
-T am fi'r eS.e
WALTER TAYLOR. Graceville, February 1.