312 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[August, 



that of the iiumps. Or when it exerts 100 horse it consumes only 198 poiimls 

 of coal per hour. 



Taylor's engine exerted IO25 horse power on an average of all the variations 

 of the power which it exerted in the year 1811, and 127} horse power in 18'12. 

 On an average of botli years it would bo 115 liorse power, and which, accord- 

 ing to the above statement of 1'98 pounds of coal, would he attended by a 

 consumption oi 227| pounds of coal per hour, that being on an assumption 

 that the average performance during the two years was 94 millions, when in 

 fact it was 953 millions. 



ON THE FORM OF SEWERS. 



A considerahle portion of the report of the Commission on " Health of 

 Towns" is devoted to the discussion of the forms of sewers, in consequence 

 of the {lertinacity of the Westminster Commission in retaining a bad form. 



Forms of Sewers. 

 Wm. Hosking, C. E. thinks the hcst form is that of the longitudinal 

 section of an egg placed with its small end down. It confines the water when 

 there is a small quantity, so that it may act upon the substances that pass 

 into the drain with most eftect, and it gives an increased space to the water 

 as the water increases ni deptli. It is quite certain that the same quantity of 

 water will carry over a quickly-curve 1 Ijottom substances which would re- 

 main upon a bottom less curved, and consequently upon a flat bottom. 



W. D. Gulhrie, C. E,, holds the same opinion. Mr. Beck, Tower Hamlets' 

 Surveyor, builds all new sewers with semicircular bottoms, as does Mr. New- 

 man, .Surrey .and Kent Surveyor. 



Mr. Cresy, C. E., says that lie has often considered the form used in the Bo- 

 rough district, and also the Westminster district, and in other districts ; and 

 his impression is, that the form which would nearest approach an egg-shape, 

 would be the preferable one. There is more economy in it, and greater 

 strength. If the bottom was narrower^it would give greater facility !or the 

 drainage, and anything deposited in the sewer would be more re.idily washed 

 away, and there would be no deposit so great as is the case at Westminster, 

 where they are obliged to cleanse them by men. The operation is a very dis- 

 agreeable one, and it is sometimes necessary to do it frequently, and it is a 

 cause of great expense and nuisance to the inhabitants. If you were to take 

 the section of an egg, I do not think it would be possible to have a better 

 form, you would obtain more strength by that than by any oilier form. 

 There is less material required in that shape than is required in the M'cst- 

 minster sewer. If you have the same quantity of material to use with the 

 egg-shape, that you have with the section of the Westminster sewer, you will 

 get a much greater capacity. In the Westminster district of sewers you have 

 footings which extend considerably on each side, and you are obliged to exca- 

 vate the whole trench to the width of those footings; and when you are at 

 the depth of 24 or i5 feet, that adds considerably to the expense. 



■ Mr. Kelscy, City Surveyor, says of his sewers, that some of them are true 

 ellipses. Inclined sides have been largely used. They were introduced by 

 my predecessor prior to 1823. He also stales the failures whicli have, ap- 

 parently, taken place in consequence of the insuflicient strength of seuers. 

 The Fleet-street sewer, built in 16G8, and varying in size from 4 ft. 3 in. by 2 

 ft. 6 in. to 4 ft. 9 in. by 3ft., and (as I recollect is noted in the record of it) 

 built with 9-in. walls and 14-in. contrefortes at intervals, fell in, at three 

 separa'e places, in 1715, 1725, and 1739, and was rebuilt with 14-in. walls. 

 The sewer of Ludgate-hiU and street, built soon after 16ti6, and varying from 

 4 ft. 2 in. by 2 ft. 9 in. to 4 ft. Gin. by 3 ft., was repaired, in 1729, from St. 

 Paul's Churchyard down to the Fleet dilch, " great part of the walls having 

 fallen in and the paved bottom washed away." In 1822 it again failed, and 

 great part was rebuilt and enlarged. The sewer at Walbrook fell in (1821), 

 and a body of earth 8 feet square and 16 feet high was washed away. In 

 1838 part of the sewer in King-street, Smithfield, fell in, leaving a space from 

 the curb on one side home to the wall of the houses on the south-east s'de. 

 The 19th Charles 11., cap. 3, sec. 46 (1667), the Act for Rebuilding the City of 

 London, now repealed as to sewers, directs that sewers 5 feet high and 3 feet 

 wide shall have side walls IJ brick thick, the top arch 1 brick on end ; the 

 bottom to be paved plain, and then 1 brick on edge circular. The ancient 

 brick arch of the Walbrook sewer, in Lotlibury, was U brick thick, having 

 stood about four hundred years, until destroyed in 1834. 



Mr. Hawksley, C.E., considers that the sewage of towns may be improved 

 in general conslruction, and rendered more economical, by the use of egg- 

 shaped sewers, built with radiating bricks. He finds an egg-shaped sewer, 

 2 ft. 9 in. high, and 2 ft. wide, may be laid at a depth of at least 8 feet for 

 about 3i. per foot, the bricks radiating, and the rim 41 inches thick. Such a 

 sewer will be large enough for two-thirds of the streets of a provincial town, 

 if the inclination be not less than 1 inch in 10 feet. Such a sewer would fre- 

 quently drain 500 or 600 houses, and would relatively answer the purpose of 

 second sized (4 ft. 6 in. by 2 ft. 6 in.) sewers in London. 



Professor Butler Williams enters into the scientific investigation at great 

 length, and proves incontcstably the superiority of the egg-sliaped sewer 

 over the Westminster flat-sided sewer. 



The condemnation of the Westminster system is indeed unequivocal, and 

 its inefficiency attested on all hands. Professor Williams proves that 66,669Z. 

 I5s. has been in the last ten years positively lost in the Westminster Com- 

 mission of Sewers, through the ignorance and perversity of its conductors. 



Mr. .Stevens, an architect and surveyor, details the notorious Notting-hill 

 case. The sewer has an arched top, arched bottom, and upright sides. There 

 are two classes of sewers built under the Westminster regulations, the one 

 being 3 feet 6 in height, and the other about 5 feet. They are both built 

 witli a semicircular arch at the top, and a segment of a circle at the bottom, 

 with upright and parallel sides. The upright walls are U brick, or 13J in. : 

 the thickness of the arch at the top 2 half bricks, or 9 inches. — " On what ac- 

 count is the extra thickness of the side walls ? Is it to protect them from the 

 lateral pressure? I think so, — Is that the effect ? In my experience I have 

 found that has not been the efi'cct. — You speak from the experience you have 

 had in the construction of sewers at Notting-hill and elsewhere? Yes. — Is 

 the bottom the segment of a large circle ? Yes. — Not semicircular ? No j 

 there does not appear to be any principle involved in the construction of this 

 sewer to provide against the crushing in of the sides. Its stability depends 

 upon the firmness of the mortar, on its being liard, and adhering to the sides 

 of the bricks. The circumstance of the wetness of the ground, in the instance 



1 refer to, prevented the mortar setting ; the sewer becoming affected by the 

 lateral pressure of the ground, the walls slid off the footings. The form of 

 the exterior of the sewer |is flat at the bottom, with footings under the side 

 walls, spreading out a considerable way on each side of the sewer : the per- 

 pendicular walls are built upon these footings. I have seen several of the 

 arched sewers, and I know of none in which a failure has taken place in the 

 9-inch arch, although but two-thirds the thickness of the side walls of the 

 Westminster sewers. The soil there (at Notting-liill) is a stifi' clay very liable 

 to sudden slips. It is filled with fissures, and in wet weather, the water find- 

 ing its way into these fissures, causes large masses to slide; and without a 

 moment's notice it will sink suddenly, so that the sewer might be subject to 

 great and sudden pressure. In the first instance we did not strut it, because 

 the ground appeared to be firm, and we thought it would stand. Afterwards 

 we strutted it, as we thought very securely, but the pressure of the ground 

 was not only sucli as to crush the ground but the struts as well, The sewer 

 is on the side of a hill, with the strata in the direction of the hill ; so that 

 the pressure was greater on one side of the sewer than on the other. It may 

 be well, perhaps, to give some account of the progress of that failure. The 

 sewer was commenced so long since as November, 1842 ; application was then 

 made to the commissioners for permission to make a sewer across the ground 

 at Notting-hill, which permission was granted. The work was contracted 

 for, and in my opinion done in a very superior manner: the bricks were 

 good, and the lime and sand of a very excellent quality. About December it 

 failed by the crushing in of the sides. The proprietor of the ground called 

 my attention to the failure in the first instance, from having observed the 

 falling of the ground on the top of the sewer, which had some time previously 

 been filled in level, but was then lying hollow. 1 went into tlie sewer, and 

 through it as far as practicable, and found that the sides liad collapsed. On 

 further examination I found that the ground had slipped to an extent of from 

 forty to fifty feet from the sewer, and upon excavating and opening the sewer 

 the width between the side walls was found to be only 1 fl. 7 in., instead of 



2 fl. 6in . the size it was originally built. The persons in attendance from 

 the commissioners reported that a failure had taken place. I was summoned 

 to attend the commissioners, and laid before them a copy of the report I iiad 

 made to my employer, stating that I believed the failure to have originated 

 in the form of the sewer, and not in any deficiency in the workmanship. The 

 commissioners however thought otherwise, and said they could allow no dif- 

 ference to be made in the form, and it must be rebuilt in the same form ; that 

 they would send a person dow n from their office to be constantly on the spot, 

 and to give directions from time to time to the workmen, in order that it 

 should be done in accordance with their regulations. The sewer was most 

 carefully rebuilt; the whole height of the sewer was strutted, parallel planks 

 of three inches in thickness being placed on each side of the sewer, and sus- 

 tained in their position by short transverse struts cut from the end of scaffold- 

 poles, and about five or six inches in diameter. There were three sets of these 

 strnttings in the height, so as to leave a very small portion cf the whole un- 

 protected. When about a hundred feet of the sewer had been constructed in 

 this way, and the ground filled in upon it, we perceived indications of a fresh 

 failure, and in three or four days after, the pressure of the ground became so 

 great, that the ends of the struts were in many cases forced through the 3- 

 inch planks, anil the planks themselves bent hollow. Hence we were obliged 

 to take it up a second time ; my employer then applied to the commissioners 

 for permission to put in a sewer of a different form in onler to ascertain, 

 whether the failure arose from a deficiency of workmanship or any inade- 

 quacy in the form. I attended the commissioners on the day when that letter 

 was read, and had a very long conference with them upon the subject ; they 



