Page:The Building News and Engineering Journal, Volume 22, 1872.djvu/204

 188 THE BUILDING NEWS. Marcu 8, 1872. Sa a al a ESE rigid, mechanical detail was praised as the > rT - perfection of correctness. Will all ow restorations, we wonder, find favour with our successors, or will the next forty years see as great a change in opinion as the last has done ? ——__>__. THE NORWICH SEWERAGE WORKS. OmeS and important sewerage works haye recently been completed at Nor- wich, from the designs and under the per- sonal superintendence of Mr. A. W. Morant, C.E., the engineer to the Norwich Board of Health. The chief features of the works are alow level sewer, a high level sewer, a pumping station near the ‘Trowse railway station, a large area of land at Crown Point, of which 250 acres are at present laid out forirrigation, anda cast-iron main, 3,190 yards in length, which conveys the sewage from the pumps to the land. An Act of Parliament having been obtained, the main sewers were commenced in August, 1868, but in the following March, owing to the great quantity of water met with in the low level excavations, the contractor for the sewers faiied to carry out the work satisfac- torily, and the Board resolved to complete the works themselves. Since that time the whole of the sewers have been entirely exe- cuted by Mr. Morant, without the interven- tion of a contractor. The low level intercepting sewers are about four miles in length, and vary in size from 3ft. Yin. by 2ft. Gin., to G6ft. by 4ft. The depth below the surface is in some places 20ft. and in others as much as S0ft., and nearly the whole length is tunnelled. The high level sewer is upwards of two and a half miles in length, and variesin size from 3ft. Yin. by 2ft. 6in., to 4ft. Gin. by 3ft. The depth below the surface is LOft. in some parts and 50ft. in others. This sewer also is chiefly executed in tunnel. The ground through which thesewers have been driven is chalk, with the exception of about 1,000 yards through sand and gravel, and a short length through peat. The high level sewer is chiefly of brickwork, but for some distance the invert and sides only are of brickwork, the arch being of concrete, made with Portland cement. The ground through which the high level sewer is driven is dry chalk, and, with the exception of several sand-galts which were met with, and which caused some trouble, the ground stood well; but in exe- cuting the low level sewer the difficulties have been enormous, and had not Mr. Morant been a man of very great energy and ability he could never have completed the works. In this portion of the work the chalk is saturated with water, and was found in some parts to be so rotten and weak that the tunnel had to be close-timbered. Some parts of the low level sewer are 20ft. below the ordinary high water level of the river (the Wensum), which is only about 3ft. above the mean level of the sea at Yarmouth. At this level the water is found to stand over the whole area of the city. The water came into the excavations so fast, that some- thing like a dozen portable engines were for a long time worked night and day to keep down the water, so that the excavation could be proceeded with. About twenty million gallons of water were raised every 24 hours, the height to which the water had to be lifted being from 40ft. to 85ft. The wells in the neighbourhood were laid dry, andthe Board obtained a supply of water for the inhabitants from the Waterworks Company, by means of stand pipes in numerous places, and by carts in other parts of the city. So heavy was the drain of water from the excavations, that in driving the sewer along King-street, where four engines were at work, a tract of marsh land of about 30 acres in extent, lying on the opposite side of the river, was drained dry to a depth of 9ft., the consequent contraction of the peat bog causing cracks all over the surface. This heavy rate of pumping necessarily threw great and unusual strain upon the temporary pumping machinery, and occasioned several delays from breakage. Some of the streets in the old part of the city are very narrow, and this obliged the sewers to be driven close beneath the walls of the houses and of several churches, but each difficulty was met and dealt with as it oc- curred, and all have been successfully over- come; the sole responsibility in the mean time, however, resting on the engineer. Tn one part an ancient valley of the chalk was met with on the line of sewer, filled up partly with clay and partly with a fine run- ning sand, and the ground was here very difficult to contend with. In one case, in sinking a shaft and sump, the pumping was discontinued, and divers were employed to sink a wooden curb 10ft. in diameter, with perforated sides. A wooden bottom was then got in, and upon that alayer of concrete was deposited, and thus a sump was formed, and the water pumped out. In this part of the work it was necessary to place the pumps at intervals of not more than 150ft. along the line of sewer. Cast-iron invert plates were employed in this portion of the work, as it was found impossible to lay pipes to take off the water to the pumps, and in some parts of it the sewer is wholly of cast-iron segments. At the point where the high level sewer joins the low level sewer, which conveys the sewage of both districts to the pumps, a leap- ing weir has been constructed, the action of which is to separate the ordinary flow of the sewage from the extraordinary flow produced by heavy rainfalls. The ordinary flow is made to pass down to the low level outfall sewer, and the storm waters to leap the weir and pass off to the river through the storm overflow channel. As this storm water will be mixed wlth only a very sniall comparative quantity of sewage, Mr. Morant has con- sidered it better, for reasons of economy of pumping, to deliver this water directly into the river. The leaping weir, we believe, was first used by Mr. Bateman on the Man- chester Waterworks, to Separate the clear water which flows from the hills in fine weather from the muddy water which comes down in wet weather, but Mr. Morant’s adaptation of the same principle to the separation of the sewage from the storm waters seems to be original. The action, in fact, is simply reversed ; in the one case the clear water is separated, and in the other the sewage, both being conveyed away to their respective destinations for use. The main low level sewer terminates in a penstock chamber about 30ft. in depth, which contains a sluice, by means of which the sewage can be shut out of the engine well during repairs, and adjoining this a grating to keep out corks, chips, &e. Thereis also at water level to catch corks and small float- ing bodies, and is found to act very bene- ficially. Numerous shafts and side entrances have been provided for access to the sewers. ‘The shafts, 5ft. to 6ft. in diameter, and some of them S0ft. to 50ft. deep, act as ventilators. In addition to these some of the working shafts were made to act as ventilators, by carrying up pipes in them as the shafts were filled up. ‘The sewers pass under the bed of thenayigable river Wensum in three places ; in one place the main sewer consists of cast- iron cylinders 5ft. diameter, bedded in Port- This work was exe- cuted by coffer-dams, half the width of the river at once. In two other parts of the works, 30in. cast-iron pipes have been laid under the bed of the river, During the time the main intercepting sewers were being constructed, numerous branch sewers, some of brickwork and others of stoneware pipes, were laid in various parts of the city and suburbs, which had not previously been drained. ‘There remains yet more to be done in this respect. The works were completed and set to work a few months ago, but much difficulty has since been experienced in consequence of the great pressure of water surrounding the sewers forcing it through the joints where- ever there was the slightest imperfection; and in some portions of the work, from accidents to the temporary pumping machinery whilst the sewers are being constructed, the water rose and partly washed the cement out of the joints before it had time to set, and at the back of the work this, of course, could not be seen. It is a matter of very great difficulty to make these leaky portions watertight, but by caulking, and in two places by iron-plate lining, a large proportion of the leakage has been stopped, and it is expected that every- thing will be in working order by May next. The total cost will be about £1 0,000, A curious circumstance occurred after the irrigation had commenced. The portion of the farm first laid out is of a sandy subsoil, about 20ft. in depth, and overlies the chalk. As the water filtered downwards numerous cir- cular holes appeared all over the land, varying from 3ft. to 20ft. in diameter, and from 3ft. to 15ft. indepth. There is little doubt thatunder each of these holes a sand-galt existed, so that probably these will ecntinue to show them- selves until they have become filled up solid, and where the sand overlies the solid chalk no depressions will occur. This theory seems to be a correct one, for upon viewing sections of sand-galts in neighbouring chalk pits they show themselves to be large conical holes in the chalk, filled, in the lower part with stones, and in the upper part with sand, but not closely packed, and the sand above slightly drops over these holes. When the water pereolates through the sand it carries down with it the particles of sand and stones and beds them solidly at the bottom, leaving a vacuity under the top soil, which then falls in, thus: Mau da = didath wilul f The pumping station consists of three engines on the rotative, expansive, and con- densing principle, the steam cylinders being 35in. diameter and the stroke 6ft. Each engine works a high-lift pump, constructed on the combined bucket and plunger prin- ciple, which raises the sewage to the land at Crown Point through the main before men- tioned, the lift being about 150ft. To each engine is also attached a low-lift pump for delivering storm waters into the river. Four Lancashire boilers are provided, each 27ft. long and 7ft. diameter. They are usually fed by means of a Giffard’s injector, but in event of this failing there isa donkey-pump. The chimney is of brickwork, 150ft. in height, 15ft. diameter at the bottom of the shaft, and 8ft. Sin. at the top. The engines, boilers, and pumps were made and fixed by Mr. Joseph Clayton, of Preston, and cost about £7,000. Besides the main engines there is a donkey-engine to drive the machinery of the workshops. ‘The engine and boiler-houses, chimney shaft, workshops, and smithy also cost about £7,000. The cast-iron pipes form- ing the pumping main, which are 20in. diameter, were cast at the Stavely Ironworks in Derbyshire, and were laid by a local con- tractor, Mr. John Downing, of Norwich.
 * land cement concrete.
 * a perforated iron trough which is kept just