Breakwater Extension.

Taranaki Daily News, Volume XLVII, Issue 794, 10 April 1905, Page 2

Breakwater Extension.

THE WORK IN FROGREttS.. Tho ques'litm of improving the harour is oiio of great important to lew Plymouth, and after an interval if sonm eighteen years tho decision o go on with the work of extending he breakwater should ho a source rf satisfaction to the community. The last section was laid as far tack as June, 1887, since when the >nly work done in connection with t has been to strengthen the structtro when deemed necessary. The ori[inal system of construction was to juild from tho bottom with concrete jloeks forming a concrete wall, and n this manner a length of 1900 feet wis laid down, 48 feet of which subsequently subsided owing to damage from storms. The Harbour Jtonrd have long realised that the harbour needs further protection from tho elements, whicli is warranted by the volume of ship ping of late years', but the lack m funds has always been the obstacle A proposal to float a loan was mooted lust year bug nothing eventuated, and more recently it was resolved tu extend the breakwater at least another 100 feet, the work to ho done out of revenue. The Hoard will finance it by means of an overdraft which it is legal to draw upon to the extent of about £IO,OOO. The worl authorised is estimated to cost £7: per foot, bill- will probably bo carried out at a lower ligure. The consulting-engineer'to tho Harbour Board (Mr V. W. Marchant, oJ Timaru), to' whom the work was entrusted, somo time ago had a con sulfation with Mr Kapier Bell, the expert on harbour construction. 11 was then agreed that it would tx impossible to follow on the old line; of laying solid concrete blocks .on -thi bottom, owing to the unstable nature of the saird bottom which has now to be contended against am which would be an insecure foiinda tion. 'Further, the continued expend iture involved in ensuring the stabi lily of tho old portion, showed thai it would be inexpedient to adopt,tin former system, which in other break waters also has not proved entirely successful. Accordingly the lines up on which! the extension is now pro eeeding were decided upon, and th( work put in hand recently, the firsl section of 14 feet being corupletce last weok. A representative of the Daily New; paid a visit to the breakwater oi Thursday, and found operations it progress. These are a source of in teresd to the uninitiated. The sys torn being followed out is sound am effective. <!reat rougty blocks of ston ( are obtained from the Harboui Board's quarry closely adjacent where an almost unlimited supply o splendid stone, known as trachyte and admirably adapted for work o this nature, is blasted at a minimun of cost. A railway lino laid alom the flat top of the breakwater con veys the stone to the scene of opera tions. On the extreme edge of th solid concrete structure is erected I gigantic crane, capable of lifting u; to forty tons weight. By means o this the huge stones (one our rcpre sontativc witnesses being 27 tons) ar hoisted from the trucks, swim; round in n kind of tip truck so o to project far over the edge, and the; dumped into the sea where required Stones of this description, weighin from 10 -to 20 tons, form, 'the outc foundation and block aftc block is deposited pell mell to fori: the body of the sea wall. When th mass is a certain distance above hig water mark, smaller , stones ar dumped into the hollows, and the the whole is levelled oft* as much a possible and solidified with rubbl and concrete. Upon the loundntioi thus formed massive concrete block weighing {JO tons each are placed am these form the flat surface of th breakwater. The averago width o the broaKwater parapet is 34 feet made up of two blocks measuring 1feot in width, with six feet of inixw concrete filled in between. The solid arity of this grea't ocean wall is fur th-cr ensured by the protection o vast quantities of stone deposited on the weather side of the wall extending out a distanco of al'out 50 feet, and on tho lee side about 30 feot. Therefore, it will jbn seen that the 31 feet parapet represents only about a third of the total width of tht broakwa'ter's base. When one sectior is levelled off and tho top block; placed in position, the railway lin< is extended on the new surface thus formed and the giant crane moved uj into position to continue its work. So securely and firmly do the to if stones fit into position that a subsi donee of even the oulor fringe ii hardly possible, and even should on; occur this would not affect the mail wall and could be' easily remediei by dumping down an additional lo of stone. Tho sea Is constant]; banking up sand against the break water and tho deposits thus" forme aid in making an impregnable sci wall. The system in practice, has much t< recommend it. Tho dumping of ston direct from truck* has cortain obvi ous disadvantages. A modern metli od Is to erect a staging and dum tho stono off the end of it, but thi is expensive and not possible of be ing carried out where the work j not extensive. Staging would cos about £7 per foot for erection, b< sides which it would always be 1 able to be swept a-way by stormi "So far as 1 am aware," I'emarkc Mr Marchant, "the system we ai following has not been tried an; where else. Its eflicioncy here is ami ly shown. It is somewhat slow, ce tainly, but it is l not nearly so cos ly as other methods, and we en show good value for every penny e: ponded. I think we arc going to d tho work very cheaply and in a fe months' timo the 'people will be a tonished at the improvement effee ed. Only very exceptional storn weather can retard the work, and v hope tp proceet} with the eonstru tion steadily without intermission, The sum of £I92Q was spent la yoir by the Hoard in now plant, T pajrs, tq p]tj plant and building quurrying stone and making ooncre blocks. Including the foreman of tl works (Mr F. Henderson), n staff 15 employees is engaged in the brea water extension work, consisting those employed at the quarry, t eomeitt mixing house, on tho truck and at Ihe breakwater work, j tho present time there are sufficie cement blocks manufactured to to up 100 feet of new wall. That the new extension will lie I improvement on tho old portion t engineer has no doubt, and in t future the expenditure of protects the completed wof.k is \ikcly to 1 very small. When the 100 feet is cor pl-etcd it will be a great improvcmei to the harbour and vessels will I üble to Ho more snugly at the whai having increased shelter from the f ry of the southerly or westerly "bus tors." Mr Marchant is a groat advopa of tho work being continuod wh( possible. Tho extension is certaf: ly a great improvement, ho said ii reply to'quostlonM, but before tl harbour could bo eonnidered satisfa tory much more remained to bo don " There are no engineering or natu al difficulties in the way," he rcmavl od, "and if the. money was avai able this could undoubtedly be max the best artificial port in New ZSei land, To make a really first-class ii nor harbour ihe breakwater should I extended at least 1000 feot, and the It would defy all weathers, and tl vessels could 1>» ulongsido. tl wharvoa without the slightest dangi in any gale. To extend the mole th distance would bring us to n dept of 215 foot at low water, spring tide: and by dredging tho harbour could 1 made to accommodate the large: vvs*<.'l§. Tho whole question is one ( ilnn-nee. The harbour in so situate that in no part of the-colony coul such work lie carried out more sui ccssl'ully and cheaply." To those who doubt tho wisdom < continuing the breakwater, even u loan has to be resorted to, thi expert opinion will be'interesting,