THE UNDERGROUND DRAINAGE.

Timaru Herald, Volume XIIC, Issue 13520, 15 February 1908, Page 3

THE UNDERGROUND DRAINAGE.

PROfiKKSS <)F THE WORK. IliiW IT IS DONE. A ■■H.r.ilil" ilJ.i.i t. r .-tiuil-d i.v.-r the underground drainage work.; yesterday, i hatted with lilt.- contractor :mil inspector, and as a result, produces the Joiiuwiug notes : - THK SEPTIC WANK. Commencing witli Messrs J''. Palli.-i-.-r and •Sou's first contract and the further *-ncl of this, ;i notable alteration in the appearance of the north end of Revenue Cliff and the adjoining shingle spit lias. been produced by tho excavation of a. huge pit, in the bottom of which the septic tank (11 feet deep) is to be cor.iiti ucted of concrete with its bottom 4 feet below high water mark. The excavation is 66 f«ct by 43 feet on the bottom, the sides are splayed 1 in 2. and the depth at the higher side is about- 57 feet, so that some thousands of yards of material have been taken out, and these; make a show in a long tipped bank on the beach. The excavation was practically finished yesterday. The material is the common Timaru clay for the greater part of the depth ; then a layer of red giavel was passed through, and beneath this a bed of compact white clay, 3 feet thick -where it was cut through. The bottom of the pit is sloping and the clay forms the floor over ;•. part- of the hole; -where the cla3" is cut thtough the next bed is porous sand, and the bottom of the excavation being below tide level there is a strong influx of salt water at high tide. AWorthington steam pump has been fixed to keep the water down. In order that the concrete bottom may be laid without loss of cement from the percolation of water, Messrs Palliser will have to lay the drains under the bottom and keep the pump going till the concrete is set—an "extra" they had not reckoned on. The donkey engine, whose boiler supplies steam for the pump is also being used to drive a row of piles to carry the iron out-fall pipe. One pile has been diiven, and it -was a tedious job, as it had to pass through the shingle-buried slope of the heavy rubble thrown over the cliff by the Railway Department. The pilecanted first one way and then another, but finally and fortunately, with the assistance of block ennd tackle, took the upright attitude deeired. Two or three more of tho row of piles that has to be driven will probably have- to pass through this heavy lubble. - The piles are to be 8 feet apart and run out aljout 60 feet, to carry the outfall pipe clear of the beach and deliver the sewage into deep water. THE MAIN OUIFALj.. Away down the face of the deep pit appears the end of the long tunnel through the Benvenue Cliff, to the borough boundary gully below the Dairy Factory. On the town side of the gully runs another tunnel which passes under tho railway to the side of the main road, and here Messis Pallisers' contract ends. The tunnel was inad-,3 just large enough for a man to work in, stooping, and the material was got rid of through adits cut out to the face of the cliff. Several pits were dug from! the summit of the cliff, by which pipts and cement- could be lowered, to sivo pulling them long distances through the tunnel. In the length ccv-ered by this contract the piptß are 15 inches in diameter, bedded on concrete, and after testing were supported by concrete on each sirte to the level of tho top of the pipe. The contractors have still some chains of pipes to lay and bed. In running the cent-ret? along the tunnel they have a handy device of a miniature tramway supported by light wooden tresslfs astride of the pipes. They have also the septic tank to build, floor, walls and cover, with attachments for controlling the inflow of sewage. The tunnel is to bi left unfilled, except where it passes under the railway, and this part is to be thoroughly filled with broken stone. The pits on the cliff top will be filled up, and the adits from tho cliff face will be built up, in such a way that in case of need the wall can be pulled out and the tunnel entered for inspection purposes or repairs, and at stated places the pipes are replaced by a short piece of open invert covered by a, moveable 6lab to permit of inspection of the flow. Owing to the low level of the Beverley street drain, very little fall could be given to this main outfall pipe, and the flow will depend partly on pressure from the higher levels. The 15-inch pipe is continued at far as the junction ot the main road and Wai-iti road, but this work belong to tlje second contract. Messrs Pallisers' work practically ends in a big " manhole " in the main north road, which is now being got realy for completion. This is of considerable depth, and will be about 5 feet square, up to 2 feet below the road way, when it will be narrowed to be closed by a single slab of stone. At present the pit is being used also for the purpose of THK SECOND CONTRACT.

Messrs Fibbes and Clyma, -who have the liist reticulation contract, have as the lower end of their work about four chains of tunnelling under the road toi connect with the first contract; the .pipes have hten laid in and ura now being packed with concrete. The tunnel is then to be filled with clay, to be well rammed, which -will be a very tedious job. From the end of .this tunnelling the contractors proceeded by open trenching. (There will be more tunnelling later on.) The trenches are now being mainly cut by means of traction eng'ne and ploughs, and finished with pick and shovel. The trendies will average 6ft. deep and 2£ft. wide; there is about 10 miles to be done under the contract, so that what with taking out and filling in, a big cruantity of shovel work has to be done.

The method of laving the pipes is interesting. For the larger sizes, 15, 12 and 9 inch, a bed of concrett is laid beneath the pipes; the smaller, 6 inch are first laid on the clay. The pipe-layer is guided by two lines of string kept tant, one for the side of the pipe line, the other for the top. The pipes are laid socket outwards, and with rubber gloves on he plasters the lower half of the socket with a cement of

"2 to 1." places tht next pipe in position, fills in the upper half of the socket, forcing the cement in with his fingers, and smoothing off with a trowel. A wet sack is placed over each joint and three days later the '"smoke test" is applied. This test is believed to be thoroughly effective. The apparatus consists of a sort of gasholder in which a dense smoke can be made by the burning of damp sacking and grease, and by means of a strong kind of bellows the smoke is forced into a leDgth of pipe, well sealed at each end. The smoke able to ooze through imperceptible cracks, and is said to indicate air-leaks that would be undiscoverable by ■' water test, except under pressure. If a jo:nt shows a leak of smoke .through imperfect cementing, the joint is chalked. the jointing picked out and made afresh. At first there was a good deal of rejointing done, but witli greater care this workhas been reduced to a minimum. In the last length, tested, some chains, on Melville Hill, only one joint received the chalk mark of" defect. "When the pipes •are p:i>sed as test-proof the next st<-p differs with the different sizes of pipe. The large pipes .laid on concrete, have more concrete packed beneath them, ami a wall of it built up on rach side nearly to the toj). The smaller pipes have lo : e shingle packed beneath them to provide :i more.' equal bearing than could be got by ramming clay about them, 'the concrete i- Uft some "davs to sel ,and then comes the filling in. "Water is run into the trench so that the spoil splashes

into it and the remarkable result is .rained that practically ,all the stuff that came out of the trench goa> back into it, wiT/fout any ramming, notwithstanding that the- pip?, and in other casts a considerable quantity of concrete occupy part of the space. The Timaru clay appears to be a pretty ci mpact substance, but to .-,ee how th=- riewlinj,i> street and the Main North road the spoil taken out lias fofeii put back, leaving a very small ridge over the large concreted pipes is to learn that it can be packed a great deal more eksely by merely throwing it into water. "What appeals to be very complete provision has bttn made for inspection of the sewers and correction of accidental stoppages. At every street intersection and at every angle, an " inspection pit" or a "manhole" is provided. 'For an inspection pit about two lengths of piping are left out, and their places are taken by a plastered concrete trough open at the top, the sides continued upward in concrete 2£ feet, and the walls capped'by a stone slab: These will be buried under the roadway, but the position of each will hi marked and mapped, and if necessary a hole can be dug in the road, and the slab reached and removed, and the pit i; large enough for a man to apply clearing tools or a flushing hose in. The manholes are similarly made at the Bottom, but the concrete walls are continued to the road surface, finished with a, stone kerb in which fits a blue stone slab. Manholes are to be made at the more important junctions and angles. One lias been made at the foot of Wai-iti road, for instance, where a 9 inch pipe coming down that road joins a 12-inch pipe from Hewlings street. The pit is much larger below ground than tile capping s ]. lD —quite a little room in fact—and as height above the invert drains is too small to permit a man to stand upright, a concreted pit is sunk beside the drain for him to stand and work in. Whtie the drains are sunk more deeply such pits will not lw necessary. The manlioie being made where the "two contracts meet, is aTso a large one, reduced to manhole size 2ft. below the road surface. Junction pipes, for connecting with drains from the houses are put in opposite every house, every section, and every probable subdivision of a section, so as to obviate the necessity for up the main pipes to insert a junction. Each junction branch is a socket, and this is closed by cementing a stoneware disc in it. Every inspection pit ,and every junction will" be marked by a hardwood peg let deep into the ground, and they win also be mapped, so that by taping off from fixed points a drain-layer can nud a junction without wasting work in exploratory excavating. Each junction is bedded on "concrete, so that it may not be disturbed by the drain-layer. It has been said that" the house junctions should be made at the same time as the mains were being laid ,but on seeing the latter work done ,it is clear that there could be nothing gained by it, whilst it would have interfered greatly with street traffic. In fact it would have been impofcible to do it without closing a street altogether. It will give no more trouble to speak of, to dig the cross-trenches independently than if they had been done at the same time with the trenches for the mains.

Mr Fibbes, one of the contractors for No. 2, told the reporter that the firm had done all the drainage -work for Dunedin for the lesb eight years, and no work had been demanded there so good as wan required and done at Timaru. Mr Marchant, lie said, had laid out a- good job, and was having a good job done. It might be costing more, but it would be cheaper and more satisfactory in the long run.

Our reporter has to thank the contractors and the inspectoi-, Mr Donn, for the information contained in the foregoing notes - .