1847.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



55 



of Ardrossan, the Troon, Peterhead, by Telford, Scarborough, by Chap- 

 man, Hartepool, and others, are worthy of remark. 



In the improvement of natural harbours, may be mentioned Sunderland, 

 Berwick, Aberdeen, Dublin, Newry, Drogheda, Leith, Belfast, and others. 

 The principle generally adopted has been to confine and direct the tidal and 

 fresh waters, by piers, in proper and sufHcient channels, whence they are 

 discharged into the ocean, so as to enable them to act with greater effect in 

 counteracting the baneful effects of the antagonist operations of the winds, 

 waves, and sand, brought in from the sea; also to increase, as far as practi- 

 cable, the receptacle for tidal and fresJi waters, and to dispose of them in 

 Buch a manner that they shall act with effect in maintaining and preserving 

 the channels. These operations, as in the case of the Clyde, are materially 

 assisted by the employment of that invaluable auxiliary, the steam-dredging 

 machine, which ought to be attached to every harbour. I must not omit to 

 mention the breakwater in Plymouth Sound, by Rennie and Whidbey, which 

 is the first and largest example of a detached mole or breakwater in this 

 country. It is a mile long, constructed in a depth varying from 5 to 8 

 fathoms at low water, formed of loose blocks of rubble, of all sizes, up to 10 

 or 12 tons weight each, thrown into the sea to form their own base and 

 slope, according to the action of the waves. The surface from low water 

 mark to its full height, which is 2 feet above high water, has been paved 

 with massnry, and at the base of the sea slope, at the level of low-water, 

 there is a berm or benching to protect it. At the western extremity alight- 

 house has been built, to point out the western or principal entrance to the 

 Sound, and a beacon on the eastern extremity points out the east entrance. 

 The whole of the work, except a portion of the masonry, which is granite, 

 has been built of limestone, brought from the adjoining shores. The inten- 

 tion of the work was to protect the Sound against the heavy swell, which 

 formerly used to roll in with considerable violence during strong westerly and 

 south-westerly gales ; this object has been completely obtained, and the 

 roadstead has been rendered perfectly secure. The work has been eminently 

 successful in every respect, for besides obtaining the desired protection, the 

 original depth of water has been preserved, the facility of ingress and egress 

 has not been diminished, but rather increased, and the cost has corresponded 

 as nearly as possible with the original estimate. 



Another class of harbours, called Floating or Wet Docks, for receiving 

 merchant vessels out of the tide or seaway, was first introduced at Liver- 

 pool about the year 1710, and wet docks have been since constructed in 

 almost all the principal ports of the kingdom — viz., London, liristol, Hidl, 

 Leith, Sunderland, as well as for the Royal Navy at Portsmouth, Plymouth, 

 Sheeruess, Chatham, and Woolwich. The East and West India Docks, by 

 Jessop, Rennie, and Ralph Walker; the London, Leith, and Dublin, by Ren- 

 nie; St. Catherine's, London, by Telford ; the New Docks at Liverpool, by 

 Hartley; at Hull, by James Walker; at Cardiff, by Cubitt ; at Newport, by 

 Green ; at Southampton, by Giles ; and the great works now in progress at 

 Birkenhead, on the Mersey, opposite Liverpool, and at Great Grimsby, by 

 Rendel, are magnificent examples of private enterprise for facilitating the 

 commerce of the empire. The design of Rennie for a grand naval arsenal on 

 the Thames, at Northfleet, immediately above Gravesend, intended as a sub- 

 stitute for the imperfect naval establishments at Deptford, Woolwich, Sheer- 

 ness, and Chatham, is worthy of remark. This magnificent design consisted 

 of six capacious basins, with a total surface of GOO acres within the walls, 

 the largest being 4U00 feet long, and 1000 feet wide, and covering 87 acres; 

 the whole to communicate with each other, and be provided with capacious 

 quays, dry docks, building-slips, and storehouses ; steam machinery for ma- 

 nufacturing cordage, blocks, anchors, flour, and bread, sawing and converting 

 timber, pumping, and working cranes; in fact, for almost every operation 

 connected with the naval service, and so systematically arranged and disposed, 

 that the required operations should succeed each other with the greatest 

 dispatch and economy, whether of time, labour, or cost. The estimate was 

 £11,OOU,000, which was perhaps more than would have been required : any 

 portion could have been executed as it was wanted, without interfering with 

 the general plan. It is to be regretted that this plan was not carried into 

 effect, for it would have repaid the cost in the increased economy of fitting 

 out fleets, and since that period about £5,000,000 have been expended on 

 tlie old establishments in the Thames and Medway, with a small degree of 

 benefit, compared with what would have been obtained from Northfleet. 

 His design also for the improvement and enlargement of Chatham Dockyard 

 is worthy of remark. It consisted of a new channel to he made for the 

 Medway below Rochester Bridge, and converting the bend of the river, in 

 front of the Dockyard, into a magnificent floating dock of aliove 100 acres, 

 and from thence making a canal, 1^ mile long, 300 feet wide, and 30 feet 

 deep, to the deep water in the Medway at Gillingham, by which means ves- 

 sels of war of the largest class could come to the Dockyard with the whole 

 of their armament, which they cannot do now ; the course to sea would have 

 been shortened, and the shallow water of the Medway avoided : thus Chat- 

 ham Dockyard would have been rendered the most convenient and extensive 

 in Europe, and its proximitj to London by a railway would have rendered 

 the yards at Deptford and Woolwich unnecessary. The estimate for this 

 work was only £700,000, whereas since that time fully as much, if not more, 

 has been spent upon Woolwich, with a very inferior result ; indeed, it is not 

 even too late to undertake this plan for Chatham now, and would well repay 

 the expenditure. In designing and carrying into eft'eet this important class 

 of public works, so as to render them successful, a thorough knowledge of 

 the nature and operation of tides, winds, currents, soundings, and all the dc- 

 par.tments of hydrography, physical geography, and geology is necessary, and 



in these sciences much is due to the exertions of Beaufort, Bullock, Wash- 

 ington, Denham, Buckland De la Beche, Lyell, Greenough, Sedgwick, Mur- 

 cbison, Phillips, and others. 



Revetments, oa Ketainino Walls. 



These, until near the latter end of the last century, had been usually built 

 with horizontal foundations and courses, the interior side being almost verti- 

 cal, and the exterior with a flat face and very little batter, or in many cases 

 vertical. The curved face retaining wall was latterly introduced, with the 

 foundation and courses inclining from the horizontal, so as to conform with 

 the radius of curvature ; this form of wall is preferable, in many cases, to 

 the old, as combining greater strength with a less section, and being more 

 convenient in other respects, and was commonly used by Rennie in his various 

 works, when applicable. 



To whom the introduction of this improved form of wall is due it is diffi- 

 cult to ascertain with accuracy; but Rennie, Ralph Walker, and Jessop were 

 amongst the first who brought it into use. A further improvement was 

 made in the retaining walls used at Sheerness in 1815 by Rennie, where the 

 foundation being composed of soft alluvial mud and quicksand, to a great 

 depth, more than usual precautions were necessary to render the walls sub- 

 stantial and secure. The object was eftected by enlarging the base, and 

 making the interior hollow, like a caisson, with the bottom in the form of 

 an inverted dome; the outer or river face being concave, and the foundation, 

 for a certain width, laid inclining at right angles to a tangent from the curved 

 face of the front of the wall ; the remainder of the foundation was horizontal, 

 and the back or land side of the wall was vertical. Thus there was both a 

 front and back wall connected together by cross walls, forming one mass ; 

 the inverted arches or domes under the hollow spaces being filled with chalk 

 and gravel concrete, and the whole resting upon a well-connected platform 

 of piles and cross-beams and planking. By thus distributing the same quan- 

 tity of materials over a greater surface, the vertical weight per square foot 

 was reduced, and the desired stability was obtained upon this very difficult 

 and treacherous foundation. Rennie had previously tried, with success, a 

 wall of a similar principle, and under similar circumstances at Grimsby. 

 General Bentham also tried a similar principle, about the same time, which 

 was not so successful, in consequence of an unsuitable form and construc- 

 tion. 



The Coffer-dams which Rennie employed for constructing the walls at 

 Sheerness are worthy of remark, as being the most extensive and difficult 

 that had been constructed up to that perioil. The bottom being solt mud to 

 a considerable depth, piles of CO feet to 80 feet in length, were necessary, 

 and when driven and braced in their places as far as practicable, chain bars 

 ami raking-sliores from the land were requisite, in order to counteract the 

 alternate pressure inwards and falling outwards, occasioned by the badness 

 of the foundation and the heavy shocks of the waves to which they were ex- 

 jjosed. In order to break the effects of the sea during storms, he employed 

 a series of old men-of-war hulks, to act as float'ug breakwaters ; these were 

 useful to a certain extent, so long as they held firm in their places ; hut at 

 times, during heavy gales, they dragged their moorings, and driving against 

 the dams, occasioned considerable damage; upon the whole, however, they 

 were useful.* In order to give greater security to the dams, and to prevent 

 leakage, a considerable quantity of grooved and tongued sheathing-piles 

 were necessary for the works ; and to eft'eet this, he invented a machine 

 worked by a steam engine, w Inch answered the purpose effectually, at a cost 

 of one-sixth of the price of manual lal)our, and as it was unsafe to withdraw 

 any of the coffer-dam piles, he made another for cutting them off at the 

 ground level, below low water, which was also found very useful. 



The dams for founding the sea-locks of the Caledonian Canal at Fort 

 William and near Inverness, by Telford, are worthy of remark. In the former 

 case, great difticulties arose, in consequence of the foundation being rock, at 

 some depth below low water ; this was overcome by ingeniously securing the 

 piles to the rock ; and in the latter case, where the bottom was soft uuid, the 

 dirticulty was obviated by liringing cargoes or masses of earth and clay from 

 a considerable distance, and afterwards driving the piles through the made 

 ground. The great dam, 1000 feet in length, for building the foundations 

 of the river-wall and New Houses of Parliament, by James Walker, is another 

 good example. The late Peter Kwart was among the first who introduced 

 cast and wrought iron for dams, for piling in general, and for wharfs ; it has 

 been since employed by Walker, Sibley, Stevenson, and others, in many 

 situations, with great success. At the Albion Mills, already mentioned as 

 the first steam-mill constructed in 1/85, by Watt and Rennie, on the hanks 

 of the Thames, close to Blackfriars Bridge, the foundation being soft mud 

 and moving sand, inverted arches were formed upon the ground, between the 

 foundation courses of the walls, so that the whole area of the building ob- 

 tained support by the same weight resting upon an increased base. 



* Fluating breakwaters nf timber tiave latterly been tried, OS a sabstitute for more solid 

 coDstructions, but ttiey tiave not liitlierto suLteeded. 



(To be cmUinued.J 



