30 



THIC CIVIL ENGINEEll AND AlKIIITECTS JOURNAL. 



[January, 



Kk;. 4. 



a~- possHilc by niraiis uf dredging \vit!i tlio coiiinion Iiag and spoon apparatus, 

 the stones were brough to tlic place in lioats, and lowcreil 1)\ a crane, iiisnch 

 a way that as soon as each stone was placed in its proper position the tciois 

 cunhi be withdrawn without dillicnlty. 



This will be understood on referring to fig. 5, which represents the lewis 

 fi\ed in a stone, ready preiiared 

 for being lowered tlirougli the 

 water into the foundation. The 

 lewis eoTisisted of two pieces of 

 iron 1! and I), and in older to 

 use it a part of the stone must 

 be cut out, sutlieieiitly wide at 

 top to receive the base of the 

 p.irt 1!, the base of thi' ojicning 

 of the stone Iteing cipial to the 

 luiitcd widlli of I) and U; A is 

 the chain suspended from the 

 arm of the crane,* and E a small 

 rope or siring, of which the end 

 is kept above w.iter, to ]inll 

 out the rectangular part U of the 

 lewis. 



It is easy to see the method of using this instrument : the piece B is first 

 inserted, and 1) is then put in tosecm-e it, when it is evident that the heavier 

 lh(; stone may be, provided it be strong enough, the more securely will it be 

 held by the lewis when suspetuled from the crane. Coueeivc the stone now 

 to have been lowered through the water, and carefully laid in its proper place 

 in the founilalion ; the chain from the barrel of the crane is then loosened, 

 and the part 11 of the lewis being slightly knocked with an iron rod from 

 abo\e, is e.isily made to ilrop down into tlie vacant space C. It is evident 

 that the fastening piece I) will then be loose, because between this and li 

 there is a sp.ice left e(|ual to the ihtt'creiu'c between the base of li, and the 

 base of the opening in the stone. D may therefore be drawn out by lueaus 

 of the string E, and II will readily follow on pulling the chain A, and the 

 lewis is again ready to be inserted in another stone. 



All the front stones of tlie foundation were laiil with a lewis of this kind, 

 as well as the backing of scpiared stones, which were jireviously scapple- 

 dresscd at tlie ([uariT. The whole of the stones in any one course, for the 

 length of tlic jiicr, were Laid of equal thicknesses ; they ranged from four to 

 seven feet long, and from three to four feet wide. As soon as one course was 

 comiilete another w,is laid, and the length of each stone being marked on the 

 longitudinal beams above the piling, it was easy to set them so as to break 

 bond, ami the whole process of tlurs building under water was eti'ected with 

 the utmost regularity, and with less dirticidty tlian could have been autiei- 

 ])atcd by the most s,anguinc advocates of the plan. 



When all the building was carried up ,is high as the sni-facc of the lowest 

 water mink of a s)n-ing tide, any irregularity on the top was taken off, and 

 the wlude surface carefully levelled, .iiid on it tlie ashlar masonry was com- 

 luenecd and carried up with a vertical batter. This work consisted of stones 

 with piclicd fronts and ehiscl-dranghts round the edges, the cmls, beds, ami 

 face, pro]ierly squared. The backing was of good conunon rubble, and the 

 whole being raised to three feet above the highest spring tides, was linished 

 otf with a heavy coiiing, inoperly dowelled, cramped, and securc<I with lead. 



" It is (piite evident that by any oilier mode of suspending the stones ex- 

 cepting that of the lewis, which could be diseii^atJed inider water, even an 

 approximation to a close joint could never have U'cu eftcclcd iu the situatiun 

 now UescribcJ, 



This work, from its situ.ition, is called the Thorn Hush Tier ; the dale of 

 its coiislriictioM wa^ IKl.'i.and uji to the present time no ajipearance of failure 

 or imperfection has been ol)served. 



Mr. Hughes then reverts to llie consideration of roller dams, and 

 )Hiiiils o\it as good examples the eorter (l.\nis of the new Houses of 

 r^irlianient, and the one constrncled at St. Katharine's Doi'k, IhiIIi of 

 which, wc are liappy to say, liave beendescrilied in the first and second 

 volumes of our joMnial, acconiiianied by the specifications. We con- 

 sider the latter ontjlit at all limes, if possible, to aeconi])anv the draw- 

 ings, as lliey at once convey to llie ))rofession the minntiie of the i-on- 

 struction, and of the inalerials used. As we liave so fully explained 

 to our readers the eonslruclion of the above works, we shall not avail 

 ourselves of any extracts from the able eonnneuls of the author in the 

 pajier now before us, but shall |iroceed at once to the otlier portion 

 explaiuing the advantages of building inverted arches. The author 

 reconiuiends, where the bottom is unsounil, to cover it entirely over 

 will) cross sleepers of iMeuiel logs, and on them to lay a covering of 

 planks closely jointed. In support of thisniethoil of construction lie idles 

 an example of the late Mr. Ueiinie,who introduced it fur the foundation 

 at the Albion Mills, close to Hl.ickfriar's Bridge. We cannot give our 

 consent to this mode of building, being decidedly averse to the intro- 

 duction of planking and piling, excepting for hydraulic works w hen 

 both are constantly niuler water ; we would at all times risk a good 

 bed of concrete over the whole surface as adopted at the WcstniinsUr 

 Bridewell, or a broad fotindation as adopted by Sir Robert Sniirke at 

 the Penitentiary, (he latter example is alluded to by the author in a 

 subsequent part of the paper. The marshy nature of the land on which 

 both those buildings were erected, and their jnvsent appear.uice in 

 ]ioint of stability clearly show that concrete may be used with safety in 

 almost, if not all situations: we have seen such ill elVects of planking 

 lor foundations of land buildings, that we dread tlic very name of it, 

 not only is it liable to rot, but also to be crushed. We sliould think 

 that the timber lonuiiig the bottom of the caisson upiui which the piers 

 of Westminster Bridge stand lias been crushed full an inch ini thick- 

 ness; here it was of no consequence, as the timber was always inider 

 water, and remains to this day sound as on the day when laid down, 

 but there are situations in which the crushing of an inch in thickness 

 may he partial .uid cause considerable settlements in the building, 

 particularly if tliere be many openings w ith arches in the superstruc- 

 ture. Tlie foUowing observations relative to Mr. Telford are well de- 

 serving tlie attention of the junior nieuibers of the profession. 



Mr. Telford in his i)r.actice as an engineer was exceedingly cautioiH, and 

 never allowed any hut his most experienced and contidential assistants to 

 have any thing to do with exploring the foundations of any buildings he was 

 about to erect. This scrutiny into the (|ualilieatious of those employed about 

 the found.itions extcudcil to the subordinate overseers, anil even to the work- 

 men, insomuch that men whose general habits had before (lasscd unnoticed, 

 and whose characters h.ad never been inquired into, did not esrajie Mr. Tel- 

 ford's observations when set to work in operations connected with the founda- 

 tions. He was accustomed to examine men so employed whom he thought 

 unsteady, and, if necessary, would reprimaud the overseers for emidoying 

 such men about the foundations in any capacity. It is evident from tliesc 

 I)recautions that Mr. Telford was well convinced how dangerous it was even 

 to receive a report of the strata from men of careless habits or inelHeient 

 knowledge, and that he also knew the consequences which might follow from 

 careless pile-driving, and, in short, from the absence of proper care in all the 

 operations connected with the coinmencement of an important structure. 



In tlie third ilivision of this paper the author makes some judicious 

 remarks on foundations of sand. Mr. Hughes then proceeds to ilescrilie 

 a very strong «)tVcr dam for a river where there is a great depth of 

 water, from this jiart of the paper containing some excellent instruc- 

 tions, we take the following extract relative to " puddle." 



Considering only the two extremes of very hard and very soft plastic clay, 

 it will be finind that the former of these, when broken np and thrown in be- 

 tween the piles, will seldom or never form a perfect dam. On the contrary, 

 vacuities will remain between the broken pieces, and it will be found exceed- 

 ingly difficidt to be.at down clay of this kind into a body snihcicntly lirm, 

 compact, .and solid to resist the eflbrts of the water to penetrate through it. 

 If, again, clay of a very soft plastic nature lie introduced, it will jiartially dis- 

 solve and combine with the water when thrown into it, so that the space be- 

 tween the piles will be tilled with a kind of mud puddle almost in a lluid 

 state, of no greater consistency and no greater capability of keeping out water 

 than mud itself. It is evident therefore that either kind of da; liy itscV 

 woidd not answer the purpose intended of forming a solid water-tight puddle. 

 All the clays, when useil in a colter-dam, require a mixture of gr.ivcl and 

 sand, or a portion of poundeil chalk will he found an excellent materkal to 

 give solidity to the soft portion of the clay, and to fill the vacuities and in- 

 terstices which may be expected to exist where the clay is of a hard and 

 lumpy descriptisn. However general may be the opinion, it is certain that 

 ouc more erroneous was uevcr entertained than that clay alone is a proper 



