HUTT RAILWAY.

Dominion, Volume 1, Issue 157, 27 March 1908, Page 5

HUTT RAILWAY.

CUFFICIENCY OF PROTECTIVE WALLS. , ; ■ HARBOUR BOARD'S REPORT. :In accordance with'a resolution passed on March 2, • tho Aeting : Engineer of tlio Harbour Board (Mr. E. D; Cachemaille) yesterday presented to the Harbour Board- a report on the sufficiency of tho: protective walls-in . course of erection by the Government in connection with tho straightening of tho Wel-lington-Hutt railway line.. Mr. Cachemaille • said that through the courtesy, of Mr. J. Burnptt, the Chief Engineer of Working Railways, he was enabled to accompany that gentleman and Messrs. F. ■W. Maclam (Inspe'ctihg Engineer) and A. C. Kooch (Residi-nt Engineer at'Petone) on. a tour of inspection during tho. recent southerly gale. Ho' continues: — " The method adopted for the cpnstruc'tion of tlio wall fe as follows:—Heavy masses of rock and boulders aro tipped from'scows on the sito of tho wall and allowed to. spread out at .'right' angles to the'direction of tho wall until they' build t)ieni3elve-s up at their, natural angle of re-pos9-of";about 1: in 1 on both sides, and fortn; a bank of' stone having a width at its foot of approximately twice its height. This foundation is'carried up to about low water level, and on it is built a wall up to the finishe4 height' of the reclamation, and having a slope on its seaward face of about 1 in 1, of-large boulders ■: carefully packed :togethor. ; .'The'jvall is backed with smaller rubbkvto a width of about four feot to provide ample .drainage, and the reclamation f spoil is tipped behind it. Outsido the wall heavy boulders are tipped up to about the level, of high-water niark to form a ' toe' to protcct the foundation from scour, and to serve to break the waves beforo they strike the wall.. .The beneficial effect of this .' tos' .where'it had .been; completed was most marked on the- occasion of. my. .visit ■to the works. while the southerly galo was' at' its height. ... ; • ,_" Thei, stability; of- a' .wair,constructed in. this manner cannot bo questioned ... . but I,'eonstruo the-question in tho Board's resolution to mean not so much"" Is the wall a- sufficient protection to tho railway ?"—a .matter over which tho.Board has absolutely no control, and in which it can havo but little interest—as' this, ' In'tho'event of-a ■wash-out occurring, will the Board's property suffer?'

" On this question, there , is absolutely no doubt-- in my mind. Outsido tho wall the ground; gradually slopes' to a depth of two fathoms'at--a; distance varying from 150 to 250 feet from tho wall; beyond this it falls, away, quickly to a depth of seven fathoms at an-arorago' distanco of 500 feet from the , wall; outside this again it slopes away gradu- ( ally till at a distance of about 1500-feet from .the.-wall there; is a ; depth of. about ten fathoms. The average:witlth'of the reclama-' tion . works is not more than about 80 or. 100 feet.-'..'Supposing an extqnsive ,wash-out. to occur, : the amount,-of, spoil that would escape into the harbour would bo comparatively small, and the probability id that it would bo spread put by the action of tho waves over the natural shelf inside the'two fathom line, and should any of it get beyond that, it would at onco fall away into deep water. :' " The question may also be asked,' ' Why should-iiot'the. Board's reclamation walls be constructed ,of rubble'instead of concrete?' .In';jeply,-'.r'. submit that this form of construction ceases, to bo economical when carried out-in-water of tho depth of that in which -Board's reclamation walls havo to' AV.bui't, unless an-ample-supply of rock is obtainable in,,the;immediate vicinity, and further, that in the case of tho Board's walls it .is essential that it should-bo possible.'to dredge, to provido deep berthago for vessels in closo proximity .to tho wall,-wliich .'.would bo impossiblo in tho caso, of a : rubble wall owmgto the great -spread of ; the toe.".: