18-13.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



■r, 



and part of the cost devoted to the new sewers we have described. We 

 think that we could point out several other improvements that might 

 have been adopted, if the commissions had been united : but we have 

 already trespassed beyond our original intention upon this portion of 

 the subject, and must now turn our attention to the more important 

 part respecting the form, construction, and expense of the present 

 sewers of the Westminster Holborn, and Finsbury, and Regent Street 

 commissions. 



We will first proceed to enquire into the present cost of con- 

 structing sewers, and see how far they might be modified, so as to in- 

 duce builders of small tenements to construct sewers, in preference to 

 cespools; in order to do this, we are at once brought to another bone 

 of contention between the present combatants; one commission con- 

 tends that the oval sewer is the best form, whilst another flatly con- 

 tradicts it, and says that sewers with upright sides are the best; we 

 must therefore first hear what Mr. Donaldson says upon the subject. 



" With respect to the form of section of sewers, our commis- 

 sioners have very wisely adhered to that, which experience has 

 proved to them to be substantial and best calculated for the purpose. 

 We are to recollect that under-ground constructions must be built so 

 as to last for ages, otherwise a continued re-building of sewers causes 

 a constant breaking up of the streets, and obstructions to thorough- 

 fares, and a suspension to a certain degree of the commerce of the 

 trades-people on the line. The sewers must be large enough not 

 merely for the ordinary service of relieving soil drainage, but also for 

 carrying off the torrents of water, which fall during violent storms. 

 Hence a large capacity must be given them. Again, this large di- 

 mension is not without a further use in enabling the officers and 

 workman to inspect and repair them with sufficient facility, the 

 width even of our second sized sewers enabling two workmen to pass 

 each other. As regards the upward sides of the sewer, it must be 

 borne in mind that all circular work constructed of brick can only be 

 formed by making the joints more open at the extrados than at the 

 intrados, for the square shape of the brick does not lend itself to 

 other than rectangular construction. Now these open joints are filled 

 ■with mortar in a moist state, and before it is set, the earth to the 

 depth of several feet is filled in, the centres are struck, and the con- 

 sequence is an irregular settlement of the whole work ; whereas with 

 spreading footings, an invert at bottom, a circular arch at top, and up- 

 right side walls, most of these inconveniences are avoided, and the 

 sewer, even if the earth be washed away at the top or sides, as 

 sometimes happens from the bursting of one of the large main pipes 

 of the water companies, stands upright and alone on its board base, 

 whereas the oval sewer must have inevitably fallen over. I may also 

 add two other important reasons for giving as much square con- 

 struction as possible to the body of the sewer, and these are, greater 

 security against imperfect workmanship, and detection of false thick- 

 nesses of work at sides. Besides, in the event of its being judged 

 expedient to increase the depth of a sewer by putting in a new bottom 

 by underpinning, this operation becomes comparatively easy with 

 upright side walls — almost impracticable when they are curved. 

 Much stress is laid in the report upon the curved side walls as ma- 

 terially aiding the rapidity of the current. But, in fact, the ordinary 

 sewage rarely rises above the invert, and when it does, there is such a 

 force in the volume of water, that no perceptible obstruction is offered 

 by the absence of the complete circular form." 



If, on comparing the sewers of the Westminster Commissioners, 

 Fig.l and 2, with those of the Holborn and Finsbury Commissioners, 

 Fig. 2 and 3, it must be seen that Mr. Donaldson's remarks about 

 circular work are completely futile, for his objections apply equally 

 to the arch and invert of the Westminster as they do to the Holborn 

 and Finsbury; and as to the sides, the radiating of the courses in the 

 oval form is so trifling, that it is not worth naming. And again, can 

 Mr. Donaldson tell us if such an accident ever occurred, as the burst- 

 ing of a main pipe, and of washing away the earth to the extent 

 of endangering an oval sewer. We have frequently heard, that 

 during the construction of the upright sewers, of their falling in ', but 



1 We could find several cases of the Westminster sewers falling in during 

 their construction, and the upright ndes bul- inn in, as at Notting Hill, and 

 also in the vicinity of the King's Road, Chelsea. But we are told by th 

 worthy chairman, that tlr-y ucre limit by private indivj luals, and not by the 

 commission. Lei us ask Mr. Di naldson. under whose direction and super, 

 ntendance arc they built? Dare a builder alter the lorm, or lay a brick con. 



never heard of such a case with the oval Bewer. 20 years ago, we 

 happen to have been engaged in th i of about 1000 feet 



of sewage of the oval form, as shown in Fig. 

 5, built upon the crown lands in the vicinity 

 of Regent's Park, and up to the present time 

 we have never heard of a single failure, 

 either during the construction or since; we 

 think this fully justifies us in pronouncing that 

 the oval form is most effective, and in point 

 of expense infinitely to be preferred. Now 

 let us compare the expense of both forms, we 

 will take the cost of the materials and labour 

 the same in both cases, Is. per foot reduced, 

 or 13/. 12-. per rod of brickwork, and Is. per cubic yard fur digging, 

 strutting, and filling in or removing the surplus ground, the top of the 

 sewer being taken as ti feet below the surface of the ground. 



Westminster Sewers. 

 Fig. 1, first class. Fig. 2, second class. 



1 7 feet brickwork 

 3 J- yards digging 



15 feet brickwork 

 3 yards digging 



Holborn and Finsbury Sewers. 



Fig. 3, first class. Fig. i, second class. 



12 feet brickwork 

 3 yards digging 



9 feet brickwork - - 9 

 2J yaids digging - - 2 4 



Fig. 5, 2 the Regent Commission sewer is built in two half brick 

 rims, and contains about the same quantity of brickwork as fig. 4, and 

 may be taken at the same cost. Thus it will be seen that in adopting 

 the oval form, there is a saving of 5s. id. per ft. in the first-class sewer, 

 and 6s. Sd. per foot in the second-class sewer. Can there then be, 

 after perusing the above calculations, a doubt as to which form of 



trary to the directions of the commissioners' surveyor; tf this be the case, 

 the commissioners tire responsible for the work and the form of the sewer, 

 and not the builder. 



- We give the preference to the oval sewer. Fig. 5, over that of Fie. 4, as 

 the larger part of the oval is downwards, which allows a greater flow o( 

 water to pass oil quicker ; we also consider that the extra hall-brick thick- 

 ness of the sides of Fig. 3, oval sewer, perfectly useless, and night with 

 safety be omitted, which would reduce the cost of the sewer, U. Sd. per foot. 



