THE RAKAIA BRIDGE.

Press, Volume XV, Issue 2084, 20 December 1869, Page 2

THE RAKAIA BRIDGE.

To the Rakaia and back in a day means going by the first train, no great hardship these summer morning. Arrived at the station ■—hey, presto! what alterations ! The booking offices and everything else have all been bodily screwed up, and brought to an elevation handy to the carriages. The platform in lieu of the shingle—a terror to poor feet—has been asphalted; the whole has been fenced in, | and the station premises present quite a proper appearance and a satisfactory one—were they only in the right place. Why passengers should " groan and sweat" under the weary walk to a remote suburb, while coals are coolly deposited at the end of Colombo street is, especially in summer weather, an exasperating fact. The itinerary of a railway passage to the Selwyn is not generally promising in incident. The old hand will note the old South road, the theatre of old performances, and indulge in recollections. The new chum will look at the crops on either side, and go in for his little speculations in the country. Meanwhile if your doctor has forbidden you to smoke, beware of travelling second class. By undergoing the ordeal of being shut up in a compartment with say a score of your fellow creatures (a majority of whom persist in closing the ! windows, smoking pipes partially smoked out the night before, and spitting on the floor), you may in one brief hour before breakfast undo the self denial of months. As we travel along, some disconsolate houses, built on spec and refused a publican's license, seem to obtrude themselves on the scene, while other publichouses in singularly remote places, appear as pledges of an unflinching faith in a great future for Canterbury, which is not yet xealised. The Selwyn bridge is rather provocative of remark. It's original construction was suoh a blunder—even the disposition of the iron girders saved from the wreck, in the present bridge over the Heathcote, is constructively so comical—the permanence of the line of rails, in case of a heavy flood, is so very doubtful, notwithstanding the money spent over this our first shingle river to be bridged, that the Selwyn is no small item in those engineering experiments which alone make Canterbury remarkable. In this mood we came to the Rakaia, and the sight of this great river whose only apparent mission is to destroy and to be bridged, took us back to some fifteen years ago, when Mr Hayhurst arriving from his station on the Ashburton, being " stuck up " with his wool, set to work there and then, built a sort of a boat, and successfully navigated over the river both wool and dray. Henceforth boats came iato use, and after the lapse of yearß the Government of the day caused two boats to be built for the special service. This piece of attention however seemed to raise the doubt whether, if boats were provided by the Government, boats would really be required. At all events, boats in turn went out of fashion, and now the traveller is carried across like merchandise, in huge horse waggons which by the way do their work very well. True, there are a few capsizes in the river now-a-days, but only with buggies. Perhaps some tramps Been to go in don't come out —who knows ? Now any «ne conversant with our shingle rivers knows it is not so difficult to make a bridge as it is to make the river run through the bridge when it is built. A bridge over the Rakaia requires to be something like three quarters of a mile long, and a bridge of this length requires many piers, and many piers are apt to become obstructive, ' aud obstructed the river goes headlong at the'

banks, and likes no better sport than to play with a good solid substantial piece of masonry, such as engineers delight in drawing so nicely and persist in putting up despite all warning and experiment —meanwhile the bridge taken in flank, iteelf become dry. A bridge, therefore, should have no artificial abutments ; wherever there is water there must be free passage for it, and to this end piers should be reduced to a minimum. These conditions of structure are evidently well comprehended by Mr White, who is the designer of the new bridge, as well as contractor for its construction ; and it is not only in the design for the bridge that these principles are recognised, but in the scaffolding (itself a j bridge), they are fully developed. In the river bed before us, along the lino of the proposed bridge, we see stages on piers crossing the three heavy streams into whioh the river is at present divided. The construction of these strikes us as both novel and ingenious, pier frames, 12 feet wide of Bcantling roughly nailed together, cross-braced, have two uprights in the centre with an interval between the pieces, down which 2£ in. artesian well pipes shod with a spike is passed; this is driven into the shingle with the ordinary 2 cwt ram used in small driving here; until an apparently solid stratum is reached, at a depth varying along the line of from Bft to 16ft. At the sides of the pier frames are similar intervals between uprights for the passage of similar pipes, so that each frame contains three pipes driven in line, strutted and braced with the rough frames of wood scantling enclosing them; the piers thus made are 24ft apart. To erect these frames on the dry shingle bed, and drive their supporting pipes through them is comparatively easy, and takes but some two hours or so for four men ; but to erect them in the boiling current of a main stream more is required. For this purpose a sliding frame is made of two 50ft spars, whose ends are supported by chains running over saddles placed in the middle of each. This is run out over the stream and the centre pipe driven. The pier frame is then hoisted and lowered over the pipe. The pipe passing through the interval left between the centre uprights. The frame being thus pinned into its place, the side pipes are driven through the intervals made for them, first at up stream, then at down stream side. The pipes being driven to the solid stratum before mentioned, the capsule is laid on the mouths of the pipes and secured to the head pieces of the framing. This completes the pier. Spars are then thrown across from pier to pier and a temporary structure is made about 7ft above the average low water line, and 2ft below the line of the proposed bridge. Such is the scaffolding that now bridges the i Rakaia, and without intending any disparagement to the design for the permanent bridge, i we must say we think the idea suggested by the employment of these pipes is well worthy of consideration. Three 2£in pipes, properly i braced with iron, instead of wood, would probably be as strong and more durable than the proposed piles of iron bark timber j one thing* is certain, the resistance of the current would be reduced to a minimum and after strength, that is the most important point. TSot do we apprehend any deficiency in strength, for the present framework roughly put together easily meets all the demands on its strength, demands not likely to be exceeded in the public traffic over the permanent structure. Mr White proposes placing a tramway along the temporary works leading direct from the shop on the bank, and so bringing his wrought timbers to their places with the least amount of turning over. We are obliged to Mr White for the information placed at our disposal and for the facilities afforded us in inspecting the works, and we wish him every success in an undertaking fraught with such positive convenience to the public, and important results to the province at large. By taking another dose of second-hand tobacco-smoke in the last train we completed our journey, and having done so we are disposed to ask why should ladies be prevented from travelling second-class on our railways, or is the railway intended only for the benefit of a privileged class—the smokers ?