LYTTELTON HARBOUR WORKS.

Press, Volume XII, Issue 1579, 28 November 1867, Page 2

LYTTELTON HARBOUR WORKS.

The following is Mr Balfour's preliminary report on the present state and future prospects of Lyttelton Harbour Works, and was forwarded to the Provincial Government on the 16th instant :— 1. Sea Wall. I have again examined this work, and have carefully considered Mr Thornton's proposals for completing the work, and the reasons for and against tieing the new face-piles to the old work, and I have come to the conclusion that it will be better to tie them.

Certainly almost no power on earth will stop the embankment if it commence to move again, but the rigidity given by tho proposed struts will go far to prevent such movement from beginning. Just as a small pebble may hold a mass at rest on an incline, though were the mass once in motion a resistance many thousand times greater would not suffice to stop it, 60 even light strutting may be effectual in preventing the bank getting under weigh again.

Mr Thornton's design for the strutting is perhaps as good as anything else which could be designed, and I should recommend its adoption! I should also recommend for adoption his suggestion to drive a second row of piles at second bay; butlshouldgofurther and drive this back row at every bay at the two worst bulges.

This will suspend the whole mass, make it less likely to yield under the pressure of loaded trucks and the tremor caused by passing locomotives, and will in all probability make the work permanent and secure. The cost of making the works as above recommended will be about £6000, a slight increase on Mr Thornton's estimate ; but I think it wiser to spend a few hundreds more/ even though it be only to attain a greater pro-

bability that the Government shall not require to spend other £5000 in making still another face to the wall. 2. Bkkakwatbb. Further inspection of this work only confirms hit opinion that there must ho some change "in t\e system on which this work is being" 7 carried on.' Even its very slow rite of progress is very seriously again-t it, and much more th >n counterbalances its actual cheapness, as what is really wanted is present shelter unit present accommodation, not only shelter and accommodation for a future generation

But the nature of the materia!'of which it j is composed is a more fital objection But little indeed of the tipped stuff appears to be in bio'ks anything like ten hundredweight in weight, while a very Urge proportion of i' seems to be little largtr than road metal, and no small quantity little better than earth Nor is this all, the rock when first tipped at least is of a very friable nature, and many of the moderate-sized blocks are certain to be broken up by the action of the sea. A breakwater, constructed as that at Officer's Point is, is real'y an artitieial beach. Were it exposed to the direct assault of the waves it would eventually assume a permanent slope, which would probably be very long indeed with the material used ; here, however, the waves run along the work, and nothing short of a solid abutment at the outer end can ensure permanence to such a structure unless it were faced with blocks which the sea could not move.

What weight these blocks would require to bo I have not experience enough of the locality to decide, but I should consider that the facing blocks should range between two tons weight and ten tons weight. Another reason against the present system of construction is the nature of the bottom, at least if the inner face of the work is intended to be used as a wharf.

The rubble siuks to a very considerable depth in the mud cortainly, and as a channel must be dredged alongside any wharf constructed there (or anywhere in the harbour) to procure conveii-nt berths for large ships, it is obvious tha* the toe of the rubble slope must be held in by sheeting piles ; and from a

few experimental bores which I have already had taken in the harbour I should think that such piles would require to be little, if anything, leas than seventy feet in length below low ivater, so as to get a really good hold sufficient to enable them to resist the great lateral pressure to which they would be exposed. This would greatly increase the cost of any such wharfage, the timber work of which alone may be safely (under) estimated al £100 per lineal yard. Add to this the present cost of the stone breakwater £30, and the wharfage, creeping on at the rate of seventyfive feet per annum, would cost £130 per yard. But this rate of progress would not suffice, and to increase it you must increase the cost of the work. To attain a rate of progress of seventy-fivo yards per annum would increase the cost to not less than £200 per yard. Such are the considerations which led to the recommendation in my last report that the sys'em of construction should be changed, and I am satisfied that the English Harbour Commissioners would also recommend some change were they fully cognizant of tho nature of the bottom and the unsatisfactory quality of the available material. So satisfied am I that some change should be made that I should recommend that the breakwater works should only be carried forward so far as to complete the portion already commenced, and that hereafter the prisoners be for tho present employed in making an embankment faced with square blocks of stone round the rocks, to connect the breakwater with the town.

The objections which have been offered to the system of construction proposed in my last report with a view to overcome the difficulties alike of the site and material may be said to be —

1. Difficulty of construction. ! 2. Want of durability. 3. (perhaps) Novelty. Noyelty. Treating them in reverse order, I may simply state with regard to novelty that a breakwater pier was constructed at Blyth by Abernethy of timber filled in with stones ; but this was on rock, and most of the foundation was dry at low water. He has, however, prepared and published designs for constructing breakwaters in ten fathoms water on similar principles. At Greenock a new deep water pier has been successfully constructed by Bell and Miller on a moderately soft mud bottom, the face stones being cut with grooves in their ends, so as to slide down on and be guided by cast-iron piles (a very similar plan to the one recommended for Lyttelton by Mr Aickin when Provincial Engineer). Moreover, many old piers by early Dutch and French engineers were constructed on similar principles. The general idea therefore is not new, though certainly the peculiarities of the site demand new adaptations of it. Durability. To attain durability I propose to use jurrab, or Swan River mahogany, for any timber work. All evidence goes to show that this timber is, for marine works, the most durable in the world, both as resisting the marine boring wormß and as standing well between wet and dry.

In Western Australia it has remained Bound in public works in salt water for (1 write from memory) some thirty years.

Moreover it is asserted, and I think with some truth, that the Officers' Point stone not only becomes harder under water but that it becomes concreted by the action of the sea Should this be the case, such a breakwater as I propose would be in the very best conditions to allow of such an action going on, as the stone will be fully exposed to the chemical action of the salt water, and at the same time thoroughly protected from its mechanical action.

In addition to this I may add that should symptoms of decay appear it will be possible to preserve the structure in various ways—by a new facing of timber—by a facing of concrete blocks—on the outside by a rubble or concrete mound of heavy blocks, and on the inside by a storm wall—or by any combination of these plans. Moreover, should the work ever give way from decay of the timber or otherwise, the worst that could possibly happen, if the rock be not concreted by the chemical action of the sea, would be that it should fall down to natural slopes; thus it would form the base of a breakwater of the more usual character, and would not tend more to fill up the harbour than the works at present carried on. Construction. The question of construction is indeed a difficult one, and should be the best excuse as well as the most urgent reason for some novelty in design, especially as in this case economy and rapidity of construction are most important elements in the problem.

After many trials and very full consideration of all the points at issue tho design shown has been arrived at, and I am sanguine that it will be found to meet in a fairly satis factory manner all the difficulties of the site. To prevent the spreading of the material (as in the present system) it is confined by timber crates or caissons. To avoid risk of unequal settlement these crates are made of a very lartie size, and are guided and supported by a sufficient number of piles driven to firm holding ground, if not to rock. The size of the crates will also, I should expect, tend to moderate, the depth to which they will settle in the mud.

The design shows a series of huge baskete forty feet long in the width of the breakwater by twenty-four feet long in the length of it; they will be built on guide piles, gradually lowered as they are built up, and as soon as they touch the mud stone will be tipped into them, and the crates aud stone will continue to be carried up till they cease to settle down and have been filled to the proper level. The main feature of the design is the use of a sufficient number of guide piles, and tho binding the sides and ends of each caisson together by an ample number of iron tie rods, which afso embrace the piles, thus tieingall together and giving the caisson sides the extra support due to the strength of the piles themselves.

All necessary details are show n in the d ings, which aro amply sufficient to work from. The system of construction would bo M follows ■• — CoKgruucTioN. Having driven one pile on either si(] o J„ % convenient manner, and forty feet (, )r proper distance) apart, the heads would D 0 cut. to proper level and sill logs temporarily rim mi' resting on the heads, mid snlnei,.nt] secured to them on these -ills a trussed travelling stage will run with pile driver at each end.

Thus a pair of piles would bo driven at once, and the sills being extended th« „„.',. pair would be driven, and so on.

The most convenient, system would be t have a numher of short pieces of tinibt>° equal in length to the distance between ca !u pile, and to arrange the travelling „».,„ fiat tho piling engines can work 9 i s fjpf • advance of their support, as in the nCtch Then as ench pile is driven, ono of tl, e B ) lct ' t lengths (*hich could be made with east ir caps to »hin on the pile heads, and Bllvo "J trouble fixing) would be shifted forwards at ! the traveller could then advance. '

A bay of twenty-four fo-t being completed and the traveler clear of ,r lhe & °» bmhUrs would hegm by wedging or otlJ. wise suspending the bottom rods from th ."** respective piles, and bolting up the *•* frames thereto and to each other and fink" 1 ' 1 on the floor planking. The side m\\ 2°\ standards being then erected the twelve-' 1 and six-inch planks would bo bolted th '"'I at intervals, as shown. ereto

I am not prepared to say whether it WO uM be safe to spike on tho intermediate side d end planks at once, but I should prefer nott do so, and to build up merely the skeleton of tho crate, lowering it into the water as f a t it was made until it rested on the mvd 8 If this plan were adopted I would Bp i feo v' JJ panel of planks to any kind of small stuff so as to keep them in shape; the panels being lowered could be fixed by a divor with easo one or two nails only being required to keen them in position until they are supported by the rubble. ' The lowest panels of planks on, tippW would commence from ways run out on tl centre and side piles, and the diver would be of use here also in spreading the material He would also spike on the next panel of planks as soon as required, and so on. I believe, however, that in ordinary weather it would be quite safe to spike all the plants at once, provided care were taken not to commence a caisson in threatening weuther and to havo an ample supply of rubble ready for tipping, so that the caisson could be rapidly ballasted whenever it was on the bottom. After it had sunk some two or three feet into the mud I should have little fear of accident If this plan answered a diver might be dispensed with. For this kind of work it is an advantage to have small material, and I would break up all large pieces, both to ensuro close packing of the tilling and to diminish the danger of the tie-rods being bent and damaged. For the same reason tho stone should be tipped clear of the ties as much as possible.

The rate of progress of suoh a work will j depend on the pile drivers and quarymon. j The caissons could be built and filled with great rapidity. Estimate. From information I poasoss, a copy of whioh has been taken by Mr Thornton, I find that any quantity of jurrah can be procured, delivered at ship's side, at from Is 6d to 2a per cubic foot, according to scantlinc, and 2s more should cover freight, &0., on a ] a rga order. I On this assumption the estimate for a lineal yard of breakwater as designed will be— 420 i cubic feet timber at 6s ... £126 3 0 1022 lbs iron, at 6d ... t ... 25 11 0 235 oubio yards rubble, at Is ... 11 15 0 £163 9 0 Or say £170. The estimate is, however, based on tho assumption that the piles require to be driven fifty feet in the mud, that they . shall bo six feet apart only, and that the caissons will sink twenty-four feet into the mud—probably experience may enable such changes to be made on these quantities as may reduce tho coat to £160 or even £150 per yard.

A length of twelve chains, or say 800 feet, would I think amply suffice for tho present wants of the Port, and this will cost £45,000 at £170 per yard, or £40,000 at £150 ' per yard. Experiment. In face of the perhaps somewhat startling novelty of the plan proposed, and also with a view to collect information as to tho length of piles required, depth of (linkage of orates or caissons, &c, I should recommend the Government to proceed at once to the erection of a single buy, a length of twenty-four foot, using the best colonial timbers which can bo had on the spot.

This experiment, if carefully conducted, will be conclusive as to the feasibility of the plan, and will enable the Government to decide as to the propriety of undertaking tho necessary length for present accommodation of shipping. The first experimental bay may afterwards bo protected by more durablo timber, or the rubble work may be carried on so as to cover it, as may be considered best.

I shall not enter minutely into a comparison of tho cost of this work with that of other plans. I have already estimated the cost of making a breakwater on tho present system available for vessels at least £200 per yard, and the breakwater in some form must be made before you can get vessels to lio alongside any other system of wharfage.

The screw-pile jetty has cost £106 per yard at least, but were it extended and mude fit for large vessels it would require to bo much stronger, and would cost at least £150 or £160, and then you must have the breakwater, and push it on too, at a greatly enhanced cost, so as to make the jetty available.

A direct railway jetty would be equally or even more objectionable without tho breakwater, and would cost quite as muoh, probably more like £200 per yard.

The sea-wall, which is really of little or no use for wharfage purposes, will have cost before completion (not counting the filling of the bay behind, but merely the original roadway) at least £104 per yard. Thus, as I said in my last report, I am still of opinion that if the proposed system answers it will more speedily and economically than any other plan which can be devised provide both wharfage and shelter for large vessels, and until such wharfage is provided the wholo railway.system must be considered incomplete, as there is little use in increasing tho facility of transporting goods from Lyttelton if the merchant is to be at the mercy of the weather, must pay heavily for lighterage, and must expose his goods to the extra risk arising from their requiring to be so often handled. On the question of dredging I shall reporS hereafter.

(Signed) James M. Bal?oue, Member Institute C.E., Colonial Marine Engineer.

P.S.—On talking over the matter of freight with a commercial friend I am led to believe that the timber for a heavy order could be landed here at a considerably lower rate than stuted above ; probably the saving might amount to as much as Is per cubic foot, which would mako the cost of the work about £20 less per lineal yard than my estimate.

J. M. B.