The following is a list of his more important works,Fragmentum Pragense evangelii S. Marci, vulgo autographi(1778); a periodical for Bohemian and Moravian Literature (1780-1787);Scriptores rerum Bohemicarum(2 vols., 1783);Geschichte der böhm. Sprache und ältern Literatur(1792);Die Bildsamkeit der slaw. Sprache(1799); aDeutsch-böhm. Wörterbuchcompiled in collaboration with Leschka-Puchmayer and Hanka (1802-1821);Entwurf eines Pflanzensystems nach Zahlen und Verhältnissen(1802);Glagolitica(1807);Lehrgebäude der böhm. Sprache(1809);Institutiones linguae slavicae dialecti veteris(1822);Entwurf zu einem allgemeinen Etymologikon der slaw. Sprachen(1813);Slowanka zur Kenntniss der slaw. Literatur(1814); and a critical edition of Jordanes,De rebus Geticis, for Pertz’sMonumenta Germaniae historica. See Palacky,J. Dobrowskys Leben und gelehrtes Wirken(1833).
The following is a list of his more important works,Fragmentum Pragense evangelii S. Marci, vulgo autographi(1778); a periodical for Bohemian and Moravian Literature (1780-1787);Scriptores rerum Bohemicarum(2 vols., 1783);Geschichte der böhm. Sprache und ältern Literatur(1792);Die Bildsamkeit der slaw. Sprache(1799); aDeutsch-böhm. Wörterbuchcompiled in collaboration with Leschka-Puchmayer and Hanka (1802-1821);Entwurf eines Pflanzensystems nach Zahlen und Verhältnissen(1802);Glagolitica(1807);Lehrgebäude der böhm. Sprache(1809);Institutiones linguae slavicae dialecti veteris(1822);Entwurf zu einem allgemeinen Etymologikon der slaw. Sprachen(1813);Slowanka zur Kenntniss der slaw. Literatur(1814); and a critical edition of Jordanes,De rebus Geticis, for Pertz’sMonumenta Germaniae historica. See Palacky,J. Dobrowskys Leben und gelehrtes Wirken(1833).
DOBRUDJA(BulgarianDobritch, RumanianDobrogea), also writtenDobrudscha, andDobruja, a region of south-eastern Europe, bounded on the north and west by the Danube, on the east by the Black Sea, and on the south by Bulgaria. Pop. (1900) 267,808; area, 6000 sq. m. The strategic importance of this territory was recognized by the Romans, who defended it on the south by “Trajan’s Wall,” a double rampart, drawn from Constantza, on the Black Sea, to the Danube. In later times it was utilized by Russians and Turks, as in the wars of 1828, 1854and 1878, when it was finally wrested from Turkey. By the treaty of Berlin, in 1878, the Russians rewarded their Rumanian allies with this land of mountains, fens and barren steppes, peopled by Turks, Bulgarians, Tatars, Jews and other aliens; while, to add to the indignation of Rumania, they annexed instead the fertile country of Bessarabia, largely inhabited by Rumans. After 1880, however, the steady decrease of aliens, and the development of the Black Sea ports, rendered the Dobrudja a source of prosperity to Rumania.
DOBSINA(Ger.Dobschau), a town of Hungary, 165 m. N.E. of Budapest by rail. Pop. (1900) 5109. It is situated in the county of Gömör, at the foot of the Radzim (3200 ft. high) in the central Carpathians, and lies to the south of the beautiful Straczena valley, watered by the river Göllnitz, and enclosed on all sides by mountains. In the vicinity are mines of iron, cobalt, copper and mercury, some of them being very ancient. But the most remarkable feature is a large cavern some 3¾ m. N.W., in which is an icefield nearly 2 acres in extent, containing formations which are at once most curious and strikingly beautiful. This cavern, which lies in the above-mentioned Straczena valley, was discovered in 1870. The place was founded in the first half of the 14th century by German miners.
DOBSON, HENRY AUSTIN(1840- ), English poet and man of letters, was born at Plymouth on the 18th of January 1840, being the eldest son of George Clarisse Dobson, a civil engineer, and on his grandmother’s side of French descent. When he was about eight years old the family moved to Holyhead, and his first school was at Beaumaris, in the Isle of Anglesea. He was afterwards educated at Coventry, and the Gymnase, Strassburg, whence he returned at the age of sixteen with the intention of becoming a civil engineer. He had a taste for art, and in his earlier years at the office continued to study it at South Kensington, at his leisure, but without definite ambition. In December 1856 he entered the Board of Trade, gradually rising to a principalship in the harbour department, from which he withdrew in the autumn of 1901. He married in 1868 Frances Mary, daughter of Nathaniel Beardmore of Broxbourne, Herts, and settled at Ealing. His official career was industrious though uneventful, but as poet and biographer he stands among the most distinguished of his time. The student of Mr Austin Dobson’s work will be struck at once by the fact that it contains nothing immature: there are nojuveniliato criticize or excuse. It was about 1864 that Mr Dobson first turned his attention to composition in prose and verse, and some of his earliest known pieces remain among his best. It was not until 1868 that the appearance ofSt Paul’s, a magazine edited by Anthony Trollope, afforded Mr Dobson an opportunity and an audience; and during the next six years he contributed to its pages some of his favourite poems, including “Tu Quoque,” “A Gentleman of the Old School,” “A Dialogue from Plato,” and “Une Marquise.” Many of his poems in their original form were illustrated—some, indeed, actually written to support illustrations. By the autumn of 1873 Mr Dobson had produced sufficient verse for a volume, and put forth hisVignettes in Rhyme, which quickly passed through three editions. During the period of their appearance in the magazine the poems had received unusual attention, George Eliot, among others, extending generous encouragement to the anonymous author. The little book at once introduced him to a larger public. The period was an interesting one for a first appearance, since the air was full of metrical experiment. Swinburne’s bold and dithyrambic excursions into classical metre had given the clue for an enlargement of the borders of English prosody; and, since it was hopeless to follow him in his own line without necessary loss of vigour, the poets of the day were looking about for fresh forms and variations. It was early in 1876 that a small body of English poets lit upon the French forms of Theodore de Banville, Marot and Villon, and determined to introduce them into English verse. Mr Austin Dobson, who had already made successful use of the triolet, was at the head of this movement, and in May 1876 he published inThe Prodigalsthe first original ballade written in English. This he followed by English versions of the rondel, rondeau and villanelle. An article in theCornhill Magazineby Mr Edmund Gosse, “A Plea for Certain Exotic Forms of Verse,” appearing in July 1877, simultaneously with Mr Dobson’s second volume,Proverbs in Porcelain, drew the general eye to the possibilities and achievements of the movement. The experiment was extremely fortunate in its introduction. Mr Dobson is above all things natural, spontaneous and unaffected in poetic method; and in his hands a sheaf of metrical forms, essentially artificial and laborious, was made to assume the colour and bright profusion of a natural product. An air of pensive charm, of delicate sensibility, pervades the whole of these fresh revivals; and it is perhaps this personal touch of humanity which has given something like stability to one side of a movement otherwise transitory in influence. The fashion has faded, but the flowers of Mr Dobson’s French garden remain bright and scented.
In 1883 Mr Dobson publishedOld-World Idylls, a volume which contains some of his most characteristic work. By this time his taste was gradually settling upon the period with which it has since become almost exclusively associated; and the spirit of the 18th century is revived in “The Ballad of Beau Brocade” and in “The Story of Rosina,” as nowhere else in modern English poetry. In “Beau Brocade,” indeed, the pictorial quality of his work, the dainty economy of eloquent touches, is at its very best: every couplet has its picture, and every picture is true and vivacious. The touch has often been likened to that of Randolph Caldecott, with which it has much in common; but Mr Dobson’s humour is not so “rollicking,” his portraiture not so broad, as that of the illustrator of “John Gilpin.” The appeal is rather to the intellect, and the touches of subdued pathos in the “Gentleman” and “Gentlewoman of the Old School” are addressed directly to the heart. We are in the 18th century, but see it through the glasses of to-day; and the soft intercepting sense of change which hangs like a haze between ourselves and the subject is altogether due to the poet’s sympathy and sensibility.At the Sign of the Lyre(1885) was the next of Mr Dobson’s separate volumes of verse, although he has added to the body of his work in a volume ofCollected Poems(1897).At the Sign of the Lyrecontains examples of all his various moods. The admirably fresh and breezy “Ladies of St James’s” has precisely the qualities we have traced in his other 18th-century poems; there are ballades and rondeaus, with all the earlier charm; and in “A Revolutionary Relic,” as in “The Child Musician” of theOld-World Idylls, the poet reaches a depth of true pathos which he does not often attempt, but in which, when he seeks it, he never fails. At the pole opposite to these are the light occasional verses, not untouched by the influence of Praed, but also quite individual, buoyant and happy. But the chief novelty inAt the Sign of the Lyrewas the series of “Fables of Literature and Art,” founded in manner upon Gay, and exquisitely finished in scholarship, taste and criticism. It is in these perhaps, more than in any other of his poems, that we see how with much felicity Mr Dobson interpenetrates the literature of fancy with the literature of judgment. After 1885 Mr Dobson was engaged principally upon critical and biographical prose, by which he has added very greatly to the general knowledge of his favourite 18th century. His biographies ofFielding(1883),Bewick(1884),Steele(1886),Goldsmith(1888),Walpole(1890) andHogarth(1879-1898) are studies marked alike by assiduous research, sympathetic presentation and sound criticism. It is particularly noticeable that Mr Dobson in his prose has always added something, and often a great deal, to our positive knowledge of the subject in question, his work as a critic never being solely aesthetic. InFour Frenchwomen(1890), in the three series ofEighteenth-Century Vignettes(1892-1894-1896), and inThe Paladin of Philanthropy(1899), which contain unquestionably his most delicate prose work, the accurate detail of each study is relieved by a charm of expression which could only be attained by a poet. In 1901 he collected his hitherto unpublished poems in a volume entitledCarmina Votiva. Possessing an exquisite talent of defined range, Mr Austin Dobson may be said in his own words to have “held his pen in trust for Art” with a service sincere and distinguished.
DOBSON, WILLIAM(1610-1646), English portrait and historical painter, was born in London. His father was master of the alienation office, but by improvidence had fallen into reduced circumstances. The son was accordingly bound an apprentice to a stationer and picture dealer in Holborn Bridge; and while in his employment he began to copy the pictures of Titian and Van Dyck. He also took portraits from life under the advice and instruction of Francis Cleyn, a German artist of considerable repute. Van Dyck, happening to pass a shop in Snow Hill where one of Dobson’s pictures was exposed, sought out the artist, and presented him to Charles I., who took Dobson under his protection, and not only sat to him several times for his own portrait, but caused the prince of Wales, Prince Rupert and many others to do the same. The king had a high opinion of his artistic ability, styled him the English Tintoretto, and appointed him serjeant-painter on the death of Van Dyck. After the fall of Charles, Dobson was reduced to great poverty, and fell into dissolute habits. He died at the early age of thirty-six. Excellent examples of Dobson’s portraits are to be seen at Blenheim, Chatsworth and several other country seats throughout England. The head in the “Decollation of St John the Baptist” at Wilton is said to be a portrait of Prince Rupert.
DOCETAE, a name applied to those thinkers in the early Christian Church who held that Christ, during his life, had not a real or natural, but only an apparent (δοκεῖν, to appear) or phantom body. Other explanations of theδόκησιςor appearance have, however, been suggested, and, in the absence of any statement by those who first used the word of the grounds on which they did so, it is impossible to determine between them with certainty. The name Docetae is first used by Theodoret (Ep.82) as a general description, and by Clement of Alexandria as the designation of a distinct sect,1of which he says that Julius Cassianus was the founder. Docetism, however, undoubtedly existed before the time of Cassianus. The origin of the heresy is to be sought in the Greek, Alexandrine and Oriental philosophizing about the imperfection or rather the essential impurity of matter. Traces of a Jewish Docetism are to be found in Philo; and in the Christian form it is generally supposed to be combated in the writings of John,2and more formally in the epistles of Ignatius.3It differed much in its complexion according to the points of view adopted by the different authors. Among the Gnostics and Manichaeans it existed in its most developed type, and in a milder form it is to be found even in the writings of the orthodox teachers. The more thoroughgoing Docetae assumed the position that Christ was born without any participation of matter; and that all the acts and sufferings of his human life, including the crucifixion, were only apparent. They denied accordingly, the resurrection and the ascent into heaven. To this class belonged Dositheus, Saturninus, Cerdo, Marcion and their followers, the Ophites, Manichaeans and others. Marcion, for example, regarded the body of Christ merely as an “umbra,” a “phantasma.” His denial (due to his abhorrence of the world) that Jesus was born or subjected to human development, is in striking contrast to the value which he sets on Christ’s death on the cross. The other, or milder school of Docetae, attributed to Christ an ethereal and heavenly instead of a truly human body. Amongst these were Valentinus, Bardesanes, Basilides, Tatian and their followers. They varied considerably in their estimation of the share which this body had in the real actions and sufferings of Christ. Clement and Origen, at the head of the Alexandrian school, took a somewhat subtle view of the Incarnation, and Docetism pervades their controversies with the Monarchians. Hilary especially illustrates the prevalence of naive Docetic views as regards the details of the Incarnation. Docetic tendencies have also been developed in later periods of ecclesiastical history, as for example by the Priscillianists and the Bogomils, and also since the Reformation by Jacob Boehme, Menno Simons and a small fraction of the Anabaptists. Docetism springs from the same roots as Gnosticism, and the Gnostics generally held Docetic views (seeGnosticism).
1Not a distinct sect, but a continuous type of Christology. Hippolytus, however (Philosophumena, viii. 8-11), speaks of a definite party who called themselves Docetae.21Ep.iv. 2, ii. 22, v. 6, 20; 2Ep.7, cf. Jerome (Dial. adv. Lucifer. § 23 “Apostolis adhuc in saeculo superstitibus, adhuc apud Judaeam Christi sanguine recenti, phantasma Domini corpus asserebatur”).3Ad Trall.9 f.,Ad Smyrn.2, 4,Ad Ephes.7. Cf. Polycarp,Ad Phil.7.
1Not a distinct sect, but a continuous type of Christology. Hippolytus, however (Philosophumena, viii. 8-11), speaks of a definite party who called themselves Docetae.
21Ep.iv. 2, ii. 22, v. 6, 20; 2Ep.7, cf. Jerome (Dial. adv. Lucifer. § 23 “Apostolis adhuc in saeculo superstitibus, adhuc apud Judaeam Christi sanguine recenti, phantasma Domini corpus asserebatur”).
3Ad Trall.9 f.,Ad Smyrn.2, 4,Ad Ephes.7. Cf. Polycarp,Ad Phil.7.
DOCHMIAC(from Gr.δοχμή, a hand’s breadth), a form of verse, consisting ofdochmiior pentasyllabic feet (usually o _ _ o -).
DOCK, a word applied to (1) a plant (see below), (2) an artificial basin for ships (see below), (3) the fleshy solid part of an animal’s tail, and (4) the railed-in enclosure in which a prisoner is placed in court at his trial. Dock (1) in O.E. isdocce, represented by Ger.Dockea-blatter, O.Fr.docque, Gael.dogha; Skeat compares Gr.δαῦκος, a kind of parsnip. Dock (2) appears in Dutch (dok) and English in the 16th century; thence it was adopted into other languages. It has been connected with Med. Lat.doga, cap, Gr.δοχή, receptacle, fromδέχεσθαι, to receive. Dock (3), especially used of a horse or dog, appears in English in the 14th century; a parallel is found in Icel.docke, stumpy tail, and Ger.Docke, bundle, skein, is also connected with it. This word has given the verb “to dock,” to cut short, curtail, especially used of the shortening of an animal’s tail by severing one or more of the vertebrae. The English Kennel Club (Rules, 1905, revised 1907) disqualifies from prize-winning dogs whose tails have been docked; several breeds are, however, excepted,e.g.varieties of terriers and spaniels, poodles, &c., and such foreign dogs as may from time to time be determined by the club. The prisoners’ dock (4) is apparently to be referred to Flem.dok, pen or hutch. It was probably first used in thieves’ slang; according to theNew English Dictionaryit was known after 1610 in “bail-dock,” a room at the corner of the Old Bailey left open at the top, “in which during the trials are put some of the malefactors” (Scots. Mag., 1753).
DOCK, in botany, the name applied to the plants constituting the sectionLapathumof the genusRumex, natural order Polygonaceae. They are biennial or perennial herbs with a stout root-stock, and glabrous linear-lanceolate or oblong-lanceolate leaves with a rounded, obtuse or hollowed base and a more or less wavy or crisped margin. The flowers are arranged in more or less crowded whorls, the whole forming a denser or looser panicle; they are generally perfect, with six sepals, six stamens and a three-sided ovary bearing three styles with much-divided stigmas. The fruit is a triangular nut enveloped in the three enlarged leathery inner sepals, one or all of which bear a tubercle. In the common or broad-leaved dock,Rumex obtusifolius, the flower-stem is erect, branching, and 18 in. to 3 ft. high, with large radical leaves, heart-shaped at the base, and more or less blunt; the other leaves are more pointed, and have shorter stalks. The whorls are many-flowered, close to the stem and mostly leafless. The root is many-headed, black externally and yellow within. The flowers appear from June to August. In autumn the whole plant may become of a bright red colour. It is a troublesome weed, common by roadsides and in fields, pastures and waste places throughout Europe. The great water dock,R. hydrolapathum, believed to be theherba britannicaof Pliny (Nat. Hist.xxv. 6), is a tall-growing species; its root is used as an antiscorbutic. Other British species areR. crispus;R. conglomeratus, the root of which has been employed in dyeing;R. sanguineus(bloody dock, or bloodwort);R. palustris;R. pulcher(fiddle dock), with fiddle-shaped leaves;R. maritimus;R. aquaticus;R. pratensis. The naturalized species,R. alpinus, or “monk’s rhubarb,” was early cultivated in Great Britain, and was accounted an excellent remedy for ague, but, like many other such drugs, is now discarded.
DOCK, in marine and river engineering. Vessels require to lie afloat alongside quays provided with suitable appliances in sheltered sites in order to discharge and take in cargoes conveniently and expeditiously; and a basin constructed for this purpose, surrounded by quay walls, is known as a dock. The term is specially applied to basins adjoining tidal rivers, or close to the sea-coast, in which the water is maintained at a fairly uniform level by gates, which are closed when the tide begins tofall, as exemplified by the Liverpool and Havre docks (figs. 1 and 2). Sometimes, however, at ports situated on tidal rivers near their tidal limit, as at Glasgow (fig. 3), Hamburg and Rouen, and at some ports near the sea-coast, such as Southampton (fig. 4) and New York, the tidal range is sufficiently moderate for dock gates to be dispensed with, and for open basins and river quays to serve for the accommodation of vessels. For ports established on the sea-coast of tideless seas, such as the Mediterranean, on account of the rivers being barred by deltas at their outlets, like the Rhone and the Tiber, and thus rendered inaccessible, open basins, provided with quays and protected by breakwaters, furnish the necessary commercial requirements for sea-going vessels, as for example at Marseilles (fig. 5), Genoa, Naples and Trieste. These open basins, however, are precisely the same as closed docks, except for the absence of dock gates, and the accommodation for shipping at the quays round basins in river ports is so frequently supplemented by river quays, that closed docks, open basins and river quays are all naturally included in the general consideration of dock works.
Low-lying land adjoining a tidal river or estuary frequently provides suitable sites for docks; for the position, being more or less inland, is sheltered; the low level reduces the excavation required for forming the docks, and enables the excavatedSites for Docks.materials to be utilized in raising the ground at the sides for quays, and the river furnishes a sheltered approach channel. Notable instances of these are the docks of the ports of London, Liverpool, South Wales, Southampton, Hull, Belfast, St Nazaire, Rotterdam, Antwerp and Hamburg. Sometimes docks are partially formed on foreshores reclaimed from estuaries, as at Hull, Grimsby, Cardiff, Liverpool, Leith and Havre; whilst at Bristol, a curved portion of the river Avon was appropriated for a dock, and a straight cut made for the river. By carrying docks across sharp bends of tidal rivers, upper and lower entrances can be provided, thereby conveniently separating the inland and sea-going traffic; and of this the London, Surrey Commercial, West India, and Victoria and Albert docks are examples on the Thames and Chatham dockyard on the Medway. Occasionally, when a small tidal river has a shallow entrance, or an estuary exhibits signs of silting up, docks alongside, formed on foreshores adjoining the sea-coast, are provided with a sheltered entrance direct from the sea,as exemplified by the Sunderland docks adjacent to the mouth of the river Wear, and the Havre docks at the outlet of the Seine estuary (fig. 2). Some old ports, originally established on sandy coasts where a creek, maintained by the influx and efflux of the tide from low-lying spaces near the shore, afforded some shelter and an outlet to the sea across the beach, have had their access improved by parallel jetties and dredging; and docks have been readily formed in the low-lying land only separated by sand dunes from the sea, as at Calais, Dunkirk (fig. 6) and Ostend (seeHarbour). In sheltered places on the sea-coast, docks have sometimes been constructed on low-lying land bordering the shore, with direct access to the sea, as at Barrow and Hartlepool; whilst at Mediterranean ports open basins have been formed in the sea, by establishing quays along the foreshore, from which wide, solid jetties, lined with quay walls, are carried into the sea at intervals at right angles to the shore, being sheltered by an outlying breakwater parallel to the coast, and reached at each end through the openings left between the projecting jetties and the breakwater, as at Marseilles (fig. 5) and Trieste, and at the extensions at Genoa (seeHarbour) and Naples. Where, however, the basins are formed within the partial protection of a bay, as in the old ports of Genoa and Naples, the requisite additional shelter has been provided by converging breakwaters across the opening of the bay; and an entrance to the port is left between the breakwaters. The two deep arms of the sea at New York, known as the Hudson and East rivers, are so protected by Staten Island and Long Island that it has been only necessary to form open basins by projecting wide jetties or quays into them from the west and east shores of Manhattan Island, and from the New Jersey and Brooklyn shores, at intervals, to provide adequate accommodation for Atlantic liners and the sea-going trade of New York.
The accessibility of a port depends upon the depth of its approach channel, which also determines the depth of the docks or basins to which it leads; for it is useless to give a depth to a dock much in excess of the depth down toApproach channels.which there is a prospect of carrying the channel by which it is reached. The great augmentation, however, in the power and capacity for work of modern dredgers, and especially of suction dredgers in sand (seeDredge), together with the increasing draught of vessels, has resulted in a considerable increase being made in the available depth of rivers and channels leading to docks, and has necessitated the making of due allowance for the possibility of a reasonable improvement in determining the depth to be given to a new dock. On the other hand, there is a limit to the deepening of an approach channel, depending upon its length, the local conditions as regards silting, and the resources and prospects of trade of the port, for every addition to the depth generally involves a corresponding increase in the cost of maintenance.
At tidal ports the available depth for vessels should be reckoned from high water of the lowest neap tides, as the standard which is certain to be reached at high tide; and the period during which docks can be entered at each tide depends upon the nature of the approach channel, the extent of the tidal range and the manner in which the entrance to the docks is effected. Thus where the tidal range is very large, as in the Severn estuary, the approach channels to some of the South Wales ports are nearly dry at low water of spring tides, and it would be impossible to make these ports accessible near low tide; whereas at high water, even of neap tides, vessels of large draught can enter their docks. At Liverpool, with a rise of 31 ft. at equinoctial spring tides, owing to the deep channel between Liverpool and Birkenhead and into the outer estuary of the Mersey in LiverpoolBay, maintained by the powerful tidal scour resulting from the filling and emptying of the large inner estuary, access to the river by the largest vessels has been rendered possible, at any state of the tide, by dredging a channel through the Mersey bar; but the docks cannot be entered till the water has risen above half-tide level, and the gates are closed directly after high water. A large floating landing-stage, however, about half a mile in length, in front of the centre of the docks, connected with the shore by several hinged bridges and rising and falling with the tide, enables Atlantic liners to come alongside and take on board or disembark their passengers at any time.
Comparatively small tidal rivers offer the best opportunity of a considerable improvement in the approach channel to a port; for they can be converted into artificially deep channels by dredging, and their necessary maintenance is somewhat aided by the increased influx and efflux of tidal water due to the lowering of the low-water line by the outflow of the ebb tide being facilitated by the deepening. Thus systematic, continuous dredging in the Tyne and the Clyde has raised the Tyne ports and Glasgow into first-class ports. In large tidal rivers and estuaries, docks should be placed alongside a concave bank which the deep navigable channel hugs, as effected at Hull and Antwerp, or close to a permanently deep channel in an estuary, such as chosen for Garston and the entrance to the Manchester ship canal at Eastham in the inner Mersey estuary, and for Grimsby and the authorized Illingham dock in the Humber estuary; for a channel carried across an estuary to deep water requires constant dredging to maintain its depth. Occasionally, extensive draining works and dredging have to be executed to form an adequately deep channel through a shifting estuary and shallow river to a port, as for instance on the Weser to Bremerhaven and Bremen, on the Seine to Honfleur and Rouen, on the Tees to Middlesborough and Stockton, on the Ribble to Preston, on the Maas to Rotterdam and on the Nervion to Bilbao (seeRiver Engineering). Southampton possesses the very rare combination of advantages of a well-sheltered and fairly deep estuary, a rise of only 12 ft. at spring tides, and a position at the head of Southampton Water at the confluence of two rivers (fig. 4), so that, with a moderate amount of dredging and the construction of quays along the lower ends of the river with a depth of 35 ft. in front of them at low water, it is possible for vessels of the largest draught to come alongside or leave the quays at any state of the tide. This circumstance has enabled Southampton to attract some of the Atlantic steamers formerly running to Liverpool.
Ports on tideless seas have to be placed where deep water approaches the shore, and where there is an absence of littoral drift. The basins of such ports are always accessible for vessels of the draught they provide for; but they require most efficient protection, and, unlike tidal ports, they are not ableonexceptional occasions to admit a vessel of larger draught than the basins have been formed to accommodate. Occasionally, an old port whose approach channel has become inadequate for modern vessels, or from which the sea has receded, has been provided with deep access from the sea by a ship canal, as exemplified by Amsterdam and Bruges; whilst Manchester has become a seaport by similar works (seeManchester Ship Canal). In such cases, however, perfectly sheltered open basins are formed inland at the head of the ship canal, in the most convenient available site; and the size of vessels that can use the port depends wholly on the dimensions and facility of access of the ship canal.
Docks require to be so designed that they may provide the maximum length of quays in proportion to the water area consistent with easy access for vessels to the quays; but often the space available does not admit of the adoption ofDesign of Docks.the best forms, and the design has to be made as suitable as practicable under the existing conditions. On this account, and owing to the small size of vessels in former times, the docks of old ports present a great variety in size and arrangement, being for the most part narrow and small, forming a sort of string of docks communicating with one another, and provided with locks or entrances at suitable points for their common use, as noticeable in the older London and Liverpool docks. Though narrow timber jetties were introduced in some of the wider London docks for increasing the length of quays by placing vessels alongside them, no definite arrangement of docks was adopted in carrying out the large Victoria and Albert docks between 1850 and 1880; whilst the Victoria dock was made wide with solid quays, provided with warehouses, projecting from the northern quay wall, thereby affording a large accommodation for vessels lying end on to the north quay, the Albert dock subsequently constructed was given about half the width of the earlier dock, but made much longer, so that vessels lie alongside the north and south quays in a long line. This change of form, however, was probably dictated by the advantage of stretching across the remainder of the wide bend, in order to obtain a second entrance in a lower reach of the river. The Tilbury docks, the latest and lowest docks on the Thames, were constructed on the most approved modern system, consisting of a series of branch docks separated by wide, well-equipped solid quays, and opening straight into a main dock or basin communicating with the entrance lock, in which vessels can turn on entering or leaving the docks (fig. 7). The most recently constructed Liverpool docks, also, at the northern end have been given this form; and the older docks adjoining them to the south have been transformed by reconstruction into a similar series of branch docks opening into a dock alongside the river wall, leading to a half-tide basin or river entrances (fig. 1).The Manchester and Salford docks were laid out on a precisely similar system, which was also adopted for the most recent docks at Dunkirk (fig. 6) and Prince’s dock at Glasgow (fig. 3), and at some of the principal Rhine ports; whilst the Alexandra dock at Hull resembles it in principle. The basins in tideless seas have naturally been long formed in accordance with this system (fig. 5). The Barry docks furnish an example of the special arrangements for a coal-shipping port, with numerous coal-tips served by sidings (fig. 8).Tidal basins, as they are termed, are generally interposed in the docks of London between the entrance locks and the docks, with the object of facilitating the passage of vessels out of and into the docks before and after high water, by lowering theTidal and half-tide basins.water in the basin as soon as the tide has risen sufficiently, and opening the lock gates directly a level has been formed with the tide in the river. Then the vessels which have collected in the basin, when level with the dock, are readily passed successively into the river. The incoming vessels are next brought into the basin, and the gates are closed; and the water in the basin having been raised to the level in the dock, the gates shutting off the basin from the dock when the water was lowered are opened, and the vessels are admitted to the dock. In this manner, by means of an inner pair of gates, the basin can be used as a large lock without unduly altering the water-level in the dock, and saves the delay of locking most of the vessels out and in, the lock being only used for the smaller vessels leaving early or coming in late on the tide. Similar tidal basins have also been provided at Cardiff, Penarth, Barry (fig. 8), Sunderland, Antwerp and other docks.The large half-tide docks introduced at the most modern Liverpool docks (fig. 1) serve a similar purpose as tidal basins; but being much larger, and approached by entrances instead of locks, the exit and entrance of vessels are effected by lowering their water-level on a rising tide, and opening the gates, which are then closed at high water to prevent the lowering of the water-level in the dock, and to avoid closing the gates against a strong issuing current.The tidal basins outside the locks at Tilbury and Barry are quite open to the tide, and have been carried down to 24 ft. and 16 ft. respectively below low water of spring tides, in order to afford vessels a deep sheltered approach to the lock in each case, available at or near low water (figs. 7 and 8). Such basins, however, open to a considerable tidal range where the water is densely charged with silt, are exposed to a large deposit in the fairly still water, and their depth has to be constantly maintained by sluicing or dredging.Where the range of tide is moderate, or on large inland rivers, docks or basins are usefully supplemented by river quays, which though subject to changes in the water-level, and exposed to currents in the river, are very convenient for access,River quays.and are sometimes very advantageously employed in regulating a river and keeping up its banks when deepened by dredging. Generally 10 to 12 ft. is the limit of the tidal range convenient for the adoption of open basins and river quays; but the banks of the Tyne have been utilized for quays, jetties and coal-staiths, with a somewhat larger maximum tidal range; and a long line of quays stretching along the right bank of the Scheldt in front of Antwerp, constructed so as to regulate this reach of the river, accommodates a large sea-going traffic, with a rise at spring tides of 15 ft.When a dock has to be formed on land, the excavation is effected by men with barrows and powerful steam navvies, loading into wagons drawn in trains by locomotives to the place of deposit, usually to raise the land at the sides for formingExcavations for docks.quays. Directly the underground water-level is reached, the water has to be removed from the excavations by pumps raising the inflowing water from sumps, lined with timber, sunk down below the lowest foundations at suitable positions, so that the lower portions of the dock walls and sills of the lock or entrance may be built out of water. A cofferdam has to be constructed extending out from the bank of the river or approach channel in front of the site of the proposed entrance or lock, so that the excavations for the entrance to the dock may be pushed forwards, and the lock or entrance built under its protection. Sometimes the lowest portion of the excavation for the dock can be accomplished economically by dredging, after the dock walls and lock have been completed and the water admitted.Where a dock is partially or wholly constructed on reclaimed land, the reclamation bank for enclosing the site and excluding the tide has to be undertaken first by tipping an embankment from each end with wagons, protected and consolidated along its outer toe by rubble stone or chalk. When the ends of the embankments are approaching one another, it is essential to connect them by a long low bank of selected materials brought up gradually in successive layers, and retaining the water in the enclosure to the level of this bank, so that the influx and efflux of the tide, filling and emptying the reclaimed area, may take place over a long length, and in smaller volume as the low bank is raised. In this way a reduction is effected of the tidal current in and out, which in the case of a large enclosure and a considerable tidal range, would create such a scour in the narrowing gap between two high embankments as to wash away their ends and prevent the closing of the gap. Occasionally the final closure is effected by lowering timber panels in grooves between a series of piles driven down at intervals across the gap. On the closing of the reclamation bank the water is pumped out; and the excavation is carried on in the ordinary manner. It is very important that such an embankment should be carried well above the level of the highest tide which might be raised by a high wind; and in exposed sites, the outer slope of the bank should be protected by pitching from the action of waves, for any overtopping or erosion of the bank might result in a large breach through it, and the flooding of the works inside.Docks are generally surrounded by walls retaining the quays, alongside which vessels lie for discharging and taking in cargoes. In order to ascertain the nature of the strata upon which these walls have to be founded, borings are taken at theFoundations for dock walls.outset to the requisite depth at intervals near the line of the walls, but inside the dock area if the piercing of quicksand is anticipated, as in excavating for the foundations, these holes might give rise to the outflow, under pressure, of underlying quicksand into the foundations. As docks are generally formed near rivers or estuaries, these strata are commonly alluvial; but being situated at some depth below the surface, they are usually fairly hard. When they consist of gravel, clay or firm sand, the walls can be founded on the natural bottom excavated a few feet below the bottom of the dock, their weight being somewhat distributed by making them rest on a broad bed of concrete filling up the excavation at the bottom. When, however, fine sand or silt charged with water, or quicksand is met with at the required depth, the necessary pumping and excavation for the foundations might occasion the influx of sand or silt with the water into the excavations, leading to settlement and slips; or the soft stratum might be too thick to remove. The wall may then be founded on bearing piles driven down to a solid stratum, and having their tops joined together by walings and planking, or by a layer of concrete, upon which the wall is built. Or the soft stratum can be enclosed with a double row of sheet piling along the front and back of the line of wall, by which it sometimes becomes sufficiently confined and consolidated to sustain the weight of the wall on a broad foundation of concrete; or it can be excavated without any danger of sand or silt running in from outside; whilst the sheet piling at the back relieves the wall to some extent from the pressure of the earth behind it, and in front retains the wall from sliding forwards. Firmer foundations have been obtained by sinking brick, concrete or masonry wells through soft ground to a solid stratum, upon which the dock wall is built. Clusters of small concrete cylinders, in sets of three in front, and a line of double cylinders at the back, were used for the foundations of the walls of Prince’s dock at Glasgow. Wells of rubble masonry were sunk in the silty foreshore of the Seine estuary for the walls of the Bellot docks at Havre; and they served as piers, connected by arches, for the foundations of a continuous dock wall above, being carried down to a considerable depth through alluvium at the St Nazaire, Bordeaux and Rochefort docks. These well foundations, derived from the old Indian system, are built up upon a curb, sometimes furnished with a cutting edge underneath, and gradually sunk by excavating inside; and eventually the central hollow is filled up solid with concrete or masonry.Fig. 9.—Havre Bellot Dock Wall.Fig. 10.—Liverpool Dock Wall.Fig. 11.—Tilbury Basin Wall.Fig. 12.—Barry Dock Wall.The walls round a dock serve as retaining walls to keep up the quays; and though they have the support of the water in front of them when the docks are in use, they have to sustain the full pressure of the filling at the back on the completion of the dock before the water is admitted. They have, accordingly, to be increased inDock walls.thickness downwards to support the pressure increasing with the depth. This pressure, with perfectly dry material, would be represented by the weight of half the prism of filling between the natural slope of the material behind and the back of the wall; but the pressure is often increased by the accumulation of water at the back, which, with fine silty backing, is liable to exert a sort of fluid pressure against the wall proportionate to the density of the mixture of silt and water. The increase of thickness towards the base used formerly to be effected by a batter on the face, as well as by steps out at the back; but the vertical form now given to the sides of large vessels necessitates a corresponding fairly vertical face for the wall, to prevent the upper part of the vessel being kept unduly away from the quay. Examples of the most modern types of dock walls are given in figs. 9 to 12.The height of a dock wall depends upon the depth of water always available for vessels, at tideless sea-ports and at ports removed from tidal influences, such as Manchester, Bruges and the ports on the Rhine; this depth should not be less than 28 to 30 ft. for large sea-going vessels, together with a margin of 5 to 8 ft. above the normal water-level for the quays, and the foundations below. At tidal ports, however, an addition has to be made equal to the difference in height between the high-water levels of spring and neap tides; so that at ports with a large tidal range, such as the South Wales ports on the Severn estuary and Liverpool, specially high dock walls are necessary. Under normal conditions, a dock wall shouldbe given a width at a height half-way between dock-bottom and quay-level, equal to one-third of its height above dock-bottom, and a width of half this height at dock-bottom.Dock walls are constructed of masonry, brickwork or concrete, or of concrete with a facing of masonry or brickwork. Masonry is adopted where large stone quarries are readily accessible, in the form of rubble masonry with dressed stone on the face, as for instance at the Hull and Barry docks, and forms a very durable wall; but strong overhead staging carrying powerful gantries is necessary for laying large blocks. Brickwork has been often used where bricks are the ordinary building material of the district or can be made on the works, and requires only ordinary scaffolding; and harder or pressed bricks are employed for the facework. Concrete is very commonly resorted to now where sand and stones are readily procured; and where clean, sharp sand and gravel are found in thick layers in the excavations for a dock, as in the alluvial strata bordering the Thames, dock walls can be constructed cheaply and economically with concrete deposited within timber framing, dispensing with regular scaffolding and skilled labour. Such walls require to be given a facing of stronger concrete, or of blue bricks, as at Tilbury, to guard against abrasion by vessels, chains and ropes; and dock walls are commonly provided at the top with granite or other hard stone coping where the wear is greatest. The foundations for dock walls are excavated in a trench below dock-bottom, only lined with timbering where the faces of the trench cannot stand for a short time without support, and with sheet piling through very unstable silt or sand; and the trench is conveniently filled up solid with concrete, carried out in short lengths in untrustworthy ground. To reduce the amount of filling behind the wall, the excavation at the back above dock-bottom, preparatory for the trench, is given as steep a slope as practicable, supported sometimes towards the base by timbering and struts; but occasionally the wall is built within a timbered trench carried down to the required depth, before the excavation for the dock in front of it has been executed, as effected at Tilbury. The filling at the back is thus reduced to a minimum, and the lower portion of the excavation can be accomplished by dredging, if expedient, after the admission of the water, the dock wall in this way being exposed to the least possible pressure behind.The walls of open basins are often constructed out of water precisely like dock walls, as in the case of the basins forming the Manchester, Bruges and Glasgow docks; and basin walls open to the tide, as at Glasgow and in the tidal basin outside Tilbury docks (fig. 7), differ only from dock walls in being exposed to variations in the pressure at the back resulting from the lowering of the water-level in front, which is, indeed, shared to some extent by the walls round closed docks where the difference in the high-water levels of springs and neaps is considerable. The walls, however, round basins in tideless seas, such as Marseilles, occasionally those inside harbours, and especially quay walls along rivers and round open basins alongside rivers, have to be constructed under water.Fig. 13.—Marseilles Quay Wall.Fig. 14.—Antwerp Quay Wall, founded by compressed air.Fig. 15.—Caracciolo Jetty Quay Wall, Genoa.Fig. 16.—Glasgow River Quay Wall.Fig. 17.—Rouen Quay Wall.At Marseilles, the simple expedient was long ago adopted of constructing the quay walls lining the basins formed in the sea, by depositing tiers of large concrete blocks on a rubble foundation, one on top of the other, till theyOpen basin and river quay walls founded under water.reached sea-level, and then building a solid masonry quay wall out of water on the top up to quay-level, faced with ashlar (fig. 13), the wall being backed by rubble for some distance behind up to the water-level. The same system was employed for the quay walls at Trieste, and at Genoa and other Italian ports. A quay wall inside Marmagao harbour, on the west coast of India, was erected on a foundation layer of rubble by the sloping-block system, to provide against unequal settlement on the soft bottom (seeBreakwater). The quay walls alongside the river Liffey, and round the adjacent basins below Dublin, were erected under water by building rubble-concrete blocks of 360 tons on staging carried out into the water, from which they were lifted one by one by a powerful floating derrick, which conveyed the block to the site, and deposited it on a levelled bottom at low tide in a depth of 28 ft., raising the wall a little above low water. After a row of these blocks had been laid, and connected together by filling the grooves formed at the sides and the interstices between the blocks with concrete, a continuous masonry wall faced with ashlar was built on the top out of water. A quay wall was built up to a little above low water on a similar principle at Cork, with three smaller blocks as a foundation, in lengths of 8 ft. Cylindrical well foundations have been extensively used for the foundations of the quay walls along the Clyde, formerly made of brick, but subsequently of concrete, sunk through a considerable variety of alluvial strata, but mostly sand and gravel fully charged with water. Compressed air in bottomless caissons has been increasingly employed in recent years for carrying down the subaqueous foundations of river quay walls, through alluvial deposits, to a solid stratum. About 1880, a long line of river quays was commenced in front of Antwerp, extending in the central portion a considerable distance out into the Scheldt, with the object of regulating the width of the river simultaneously with the provision of deep quays for sea-going vessels; and the quay wall was erected, out of water, on the flat tops of a series of wrought-iron caissons, 82 ft. long and 29½ ft. wide, constructed on shore, floated out one by one to their site in the river between two barges, and gradually lowered as the wall was built up inside a plate-iron enclosure round the roof of the caisson, which was eventually sunk by aid of compressed air through the bed of the river to a compact stratum (fig. 14). The weight of the wall counteracted the tendency of the caisson and the enclosure above it to float; and the caisson, furnished with seven circular wrought-iron shafts, provided with air-locks at the top for the admission of men and materials and for the removal of the excavations, was gradually carried down by excavating inside the working chamber at the bottom, 6¼ ft. high, till a good foundation was reached. The working chamber was then filled with concrete through some of the shafts, the plate-iron sides of the upper enclosure were removed to be used for another length of wall, the shafts were drawn out and the hollows left by them filled with concrete, the apertures between adjacent lengths were closed at each face with wooden panels and filled with concrete, and a continuous quay wall was completed above. The most recent quay walls constructed in the old harbourat Genoa were founded under water on a rubble mound in a similar manner by the aid of compressed air (fig. 15). Quay walls also on the Clyde have been founded on caissons, consisting of a bottomless steel structure, surmounted by a brick superstructure having hollows filled with concrete, in lengths of 80 ft. and 27 ft., and widths of 18 ft. and 21 ft. respectively, carried down by means of compressed air from 54 to 70 ft. below quay-level, on the top of which a continuous wall of concrete, faced with brickwork, and having a granite coping, was built up from near low-water level (fig. 16). In many cases where soft strata extend to considerable depths, river quays and basin walls have been constructed by building a light quay wall upon a series of bearing and raking piles driven into, and if possible through, the soft alluvium. Thus the walls along the Seine, and round the basins at Rouen, were built upon bearing piles carried down through the alluvial bed of the river to the chalk. The lower portion of the quay wall was constructed of concrete faced with brickwork within water-tight timber caissons, resting upon the piles at a depth of 9¾ ft. below low water; and upon this a rubble wall faced with bricks was erected from low water to quay-level, backed by rubble stone laid on a timber flooring supported by piles, together with chalk, to form a quay right back to the top of the slope of the bank of the deepened river (fig. 17). The quay walls of the open basins bordering the Hudson river at New York have had, in certain parts, to be founded on bearing piles combined with raking piles, driven into a thick bed of soft silt where no firm stratum could be reached, and where, therefore, the weight could only be borne by the adherence of the long piles in the silt. Before driving the piles, however, the silt round the upper part of the piles and under the quay wall was consolidated by depositing small stones in a trench dredged to a depth of 30 ft. below low water; the piles were driven through these stones, and were further kept in place by a long toe of rubble stone in front and a backing of rubble stone behind carried nearly up to quay-level, behind which a light filling of ashes and earth was raised to quay-level. The slight quay wall resting upon the front rows of bearing piles was carried up under water by 70-ton concrete blocks deposited by means of a floating derrick; and the upper part of the wall was built of concrete faced with ashlar masonry (fig. 18). The basin and quay walls at Bremen, Bremerhaven and Hamburg were built on a series of bearing and raking piles driven down to a firm stratum, the wall being begun a few feet below low water. At Southampton, ferro-concrete piles were employed in constructing the deep quays; and a wharfing of timber pilework has been frequently used for river quays.Where the increase of trade is moderate and the conditions of the traffic permit, and also at coal-shipping ports, economy in construction is obtained by giving sloping sides to a portion of a dock in place of dock walls, the slope being pitched where necessary with stone; and the length of the slope projecting into a dock is sometimes reduced by substituting sheet piling for the slope at the toe up to a certain height. By this arrangement jetties can be carried out across the slope as required, enabling vessels to lie against their ends; and coal-tips are very conveniently extended out across the slope at suitable intervals (fig. 8).As dock walls, especially before the admission of water into the dock, constitute high retaining walls, not infrequently founded upon soft or slippery strata, and backed up with the excavated materials from alluvial beds, into which water is liable to percolate,Failures of dock walls.they are naturally exposed under unfavourable conditions to the danger of failure. A dock wall erected on unsatisfactory foundations is liable, where the bottom is soft, to settle down at its toe, owing to the pressure at the back, and to fall forwards into the dock, as occurred at Belfast; or where the silty bottom slips forward under the weight of the backing, the wall may follow the slip at the bottom and settle down at the back, falling to some extent backwards, as exemplified by the failure of the Empress basin wall at Southampton. The most common form, however, of failure is the sliding forwards of a dock wall, with little or no subsidence, on a silty or slippery stratum under the pressure imposed by the backing. Thus the Kidderpur dock walls furnish an instance of sliding forwards on muddy silt, and part of the South West India dock walls on two underlying, detached, slippery seams of London clay.To avoid these failures with untrustworthy foundations, great care has to be exercised in selecting the best hard material available, unaffected by water, for the backing, which should be brought up in thin, horizontal layers carefully consolidated; and where there is a possibility of water accumulating at the back, pipes should be introduced at intervals near the bottom right through the wall in building it, and rubble stone deposited close to the back of the wall, so as to carry off any water from behind, these pipes being stopped up just before the water is let into the dock. These precautions, moreover, are assisted by reducing the amount of backing to a minimum in the construction of the wall, best effected by building the wall inside a timbered trench. The liability to slide forwards can be obviated by carrying down the foundations of the wall sufficiently below dock-bottom to provide an efficient buttress of earth in front of the wall, and also by making the base of the wall slope down towards the back, thereby forcing the wall in sliding forwards to mount the slope, or to push forward a larger mass of earth; whilst a row of sheet piling in front of the foundations offers a very effectual impediment to a forward movement, and, in combination with bearing piles, prevents settlement at the toe in soft ground. In very treacherous foundations it may be advisable to defer the completion of the backing till after the admission of the water; but the additional stability given to a retaining wall or reservoir dam by an ample batter in front, is precluded in dock walls by the modern requirements of vessels.Fig. 18.—New York Quay Wall, Hudson river.Silt accumulates in docks where the lowering of the water-level by locking, the drawing down of half-tide basins, and the raising of the water at spring tides, involve the admission of considerable volumes of tidal water heavily charged with silt, which is deposited in still water and has to be periodicallyMaintenance of depth.removed by dredging. To avoid this, the water is sometimes replenished from some clear inland source, an arrangement adopted at some of the South Wales ports opening into the muddy Severn estuary, and at the Alexandra dock, Hull, to exclude the silty waters of the Humber. At the Kidderpur docks on the Húgli, the water from the river for replenishing the docks is conducted by a circuitous canal, in which it deposits its burden of silt before it is pumped into the docks.
Docks require to be so designed that they may provide the maximum length of quays in proportion to the water area consistent with easy access for vessels to the quays; but often the space available does not admit of the adoption ofDesign of Docks.the best forms, and the design has to be made as suitable as practicable under the existing conditions. On this account, and owing to the small size of vessels in former times, the docks of old ports present a great variety in size and arrangement, being for the most part narrow and small, forming a sort of string of docks communicating with one another, and provided with locks or entrances at suitable points for their common use, as noticeable in the older London and Liverpool docks. Though narrow timber jetties were introduced in some of the wider London docks for increasing the length of quays by placing vessels alongside them, no definite arrangement of docks was adopted in carrying out the large Victoria and Albert docks between 1850 and 1880; whilst the Victoria dock was made wide with solid quays, provided with warehouses, projecting from the northern quay wall, thereby affording a large accommodation for vessels lying end on to the north quay, the Albert dock subsequently constructed was given about half the width of the earlier dock, but made much longer, so that vessels lie alongside the north and south quays in a long line. This change of form, however, was probably dictated by the advantage of stretching across the remainder of the wide bend, in order to obtain a second entrance in a lower reach of the river. The Tilbury docks, the latest and lowest docks on the Thames, were constructed on the most approved modern system, consisting of a series of branch docks separated by wide, well-equipped solid quays, and opening straight into a main dock or basin communicating with the entrance lock, in which vessels can turn on entering or leaving the docks (fig. 7). The most recently constructed Liverpool docks, also, at the northern end have been given this form; and the older docks adjoining them to the south have been transformed by reconstruction into a similar series of branch docks opening into a dock alongside the river wall, leading to a half-tide basin or river entrances (fig. 1).The Manchester and Salford docks were laid out on a precisely similar system, which was also adopted for the most recent docks at Dunkirk (fig. 6) and Prince’s dock at Glasgow (fig. 3), and at some of the principal Rhine ports; whilst the Alexandra dock at Hull resembles it in principle. The basins in tideless seas have naturally been long formed in accordance with this system (fig. 5). The Barry docks furnish an example of the special arrangements for a coal-shipping port, with numerous coal-tips served by sidings (fig. 8).
Tidal basins, as they are termed, are generally interposed in the docks of London between the entrance locks and the docks, with the object of facilitating the passage of vessels out of and into the docks before and after high water, by lowering theTidal and half-tide basins.water in the basin as soon as the tide has risen sufficiently, and opening the lock gates directly a level has been formed with the tide in the river. Then the vessels which have collected in the basin, when level with the dock, are readily passed successively into the river. The incoming vessels are next brought into the basin, and the gates are closed; and the water in the basin having been raised to the level in the dock, the gates shutting off the basin from the dock when the water was lowered are opened, and the vessels are admitted to the dock. In this manner, by means of an inner pair of gates, the basin can be used as a large lock without unduly altering the water-level in the dock, and saves the delay of locking most of the vessels out and in, the lock being only used for the smaller vessels leaving early or coming in late on the tide. Similar tidal basins have also been provided at Cardiff, Penarth, Barry (fig. 8), Sunderland, Antwerp and other docks.
The large half-tide docks introduced at the most modern Liverpool docks (fig. 1) serve a similar purpose as tidal basins; but being much larger, and approached by entrances instead of locks, the exit and entrance of vessels are effected by lowering their water-level on a rising tide, and opening the gates, which are then closed at high water to prevent the lowering of the water-level in the dock, and to avoid closing the gates against a strong issuing current.
The tidal basins outside the locks at Tilbury and Barry are quite open to the tide, and have been carried down to 24 ft. and 16 ft. respectively below low water of spring tides, in order to afford vessels a deep sheltered approach to the lock in each case, available at or near low water (figs. 7 and 8). Such basins, however, open to a considerable tidal range where the water is densely charged with silt, are exposed to a large deposit in the fairly still water, and their depth has to be constantly maintained by sluicing or dredging.
Where the range of tide is moderate, or on large inland rivers, docks or basins are usefully supplemented by river quays, which though subject to changes in the water-level, and exposed to currents in the river, are very convenient for access,River quays.and are sometimes very advantageously employed in regulating a river and keeping up its banks when deepened by dredging. Generally 10 to 12 ft. is the limit of the tidal range convenient for the adoption of open basins and river quays; but the banks of the Tyne have been utilized for quays, jetties and coal-staiths, with a somewhat larger maximum tidal range; and a long line of quays stretching along the right bank of the Scheldt in front of Antwerp, constructed so as to regulate this reach of the river, accommodates a large sea-going traffic, with a rise at spring tides of 15 ft.
When a dock has to be formed on land, the excavation is effected by men with barrows and powerful steam navvies, loading into wagons drawn in trains by locomotives to the place of deposit, usually to raise the land at the sides for formingExcavations for docks.quays. Directly the underground water-level is reached, the water has to be removed from the excavations by pumps raising the inflowing water from sumps, lined with timber, sunk down below the lowest foundations at suitable positions, so that the lower portions of the dock walls and sills of the lock or entrance may be built out of water. A cofferdam has to be constructed extending out from the bank of the river or approach channel in front of the site of the proposed entrance or lock, so that the excavations for the entrance to the dock may be pushed forwards, and the lock or entrance built under its protection. Sometimes the lowest portion of the excavation for the dock can be accomplished economically by dredging, after the dock walls and lock have been completed and the water admitted.
Where a dock is partially or wholly constructed on reclaimed land, the reclamation bank for enclosing the site and excluding the tide has to be undertaken first by tipping an embankment from each end with wagons, protected and consolidated along its outer toe by rubble stone or chalk. When the ends of the embankments are approaching one another, it is essential to connect them by a long low bank of selected materials brought up gradually in successive layers, and retaining the water in the enclosure to the level of this bank, so that the influx and efflux of the tide, filling and emptying the reclaimed area, may take place over a long length, and in smaller volume as the low bank is raised. In this way a reduction is effected of the tidal current in and out, which in the case of a large enclosure and a considerable tidal range, would create such a scour in the narrowing gap between two high embankments as to wash away their ends and prevent the closing of the gap. Occasionally the final closure is effected by lowering timber panels in grooves between a series of piles driven down at intervals across the gap. On the closing of the reclamation bank the water is pumped out; and the excavation is carried on in the ordinary manner. It is very important that such an embankment should be carried well above the level of the highest tide which might be raised by a high wind; and in exposed sites, the outer slope of the bank should be protected by pitching from the action of waves, for any overtopping or erosion of the bank might result in a large breach through it, and the flooding of the works inside.
Docks are generally surrounded by walls retaining the quays, alongside which vessels lie for discharging and taking in cargoes. In order to ascertain the nature of the strata upon which these walls have to be founded, borings are taken at theFoundations for dock walls.outset to the requisite depth at intervals near the line of the walls, but inside the dock area if the piercing of quicksand is anticipated, as in excavating for the foundations, these holes might give rise to the outflow, under pressure, of underlying quicksand into the foundations. As docks are generally formed near rivers or estuaries, these strata are commonly alluvial; but being situated at some depth below the surface, they are usually fairly hard. When they consist of gravel, clay or firm sand, the walls can be founded on the natural bottom excavated a few feet below the bottom of the dock, their weight being somewhat distributed by making them rest on a broad bed of concrete filling up the excavation at the bottom. When, however, fine sand or silt charged with water, or quicksand is met with at the required depth, the necessary pumping and excavation for the foundations might occasion the influx of sand or silt with the water into the excavations, leading to settlement and slips; or the soft stratum might be too thick to remove. The wall may then be founded on bearing piles driven down to a solid stratum, and having their tops joined together by walings and planking, or by a layer of concrete, upon which the wall is built. Or the soft stratum can be enclosed with a double row of sheet piling along the front and back of the line of wall, by which it sometimes becomes sufficiently confined and consolidated to sustain the weight of the wall on a broad foundation of concrete; or it can be excavated without any danger of sand or silt running in from outside; whilst the sheet piling at the back relieves the wall to some extent from the pressure of the earth behind it, and in front retains the wall from sliding forwards. Firmer foundations have been obtained by sinking brick, concrete or masonry wells through soft ground to a solid stratum, upon which the dock wall is built. Clusters of small concrete cylinders, in sets of three in front, and a line of double cylinders at the back, were used for the foundations of the walls of Prince’s dock at Glasgow. Wells of rubble masonry were sunk in the silty foreshore of the Seine estuary for the walls of the Bellot docks at Havre; and they served as piers, connected by arches, for the foundations of a continuous dock wall above, being carried down to a considerable depth through alluvium at the St Nazaire, Bordeaux and Rochefort docks. These well foundations, derived from the old Indian system, are built up upon a curb, sometimes furnished with a cutting edge underneath, and gradually sunk by excavating inside; and eventually the central hollow is filled up solid with concrete or masonry.
The walls round a dock serve as retaining walls to keep up the quays; and though they have the support of the water in front of them when the docks are in use, they have to sustain the full pressure of the filling at the back on the completion of the dock before the water is admitted. They have, accordingly, to be increased inDock walls.thickness downwards to support the pressure increasing with the depth. This pressure, with perfectly dry material, would be represented by the weight of half the prism of filling between the natural slope of the material behind and the back of the wall; but the pressure is often increased by the accumulation of water at the back, which, with fine silty backing, is liable to exert a sort of fluid pressure against the wall proportionate to the density of the mixture of silt and water. The increase of thickness towards the base used formerly to be effected by a batter on the face, as well as by steps out at the back; but the vertical form now given to the sides of large vessels necessitates a corresponding fairly vertical face for the wall, to prevent the upper part of the vessel being kept unduly away from the quay. Examples of the most modern types of dock walls are given in figs. 9 to 12.
The height of a dock wall depends upon the depth of water always available for vessels, at tideless sea-ports and at ports removed from tidal influences, such as Manchester, Bruges and the ports on the Rhine; this depth should not be less than 28 to 30 ft. for large sea-going vessels, together with a margin of 5 to 8 ft. above the normal water-level for the quays, and the foundations below. At tidal ports, however, an addition has to be made equal to the difference in height between the high-water levels of spring and neap tides; so that at ports with a large tidal range, such as the South Wales ports on the Severn estuary and Liverpool, specially high dock walls are necessary. Under normal conditions, a dock wall shouldbe given a width at a height half-way between dock-bottom and quay-level, equal to one-third of its height above dock-bottom, and a width of half this height at dock-bottom.
Dock walls are constructed of masonry, brickwork or concrete, or of concrete with a facing of masonry or brickwork. Masonry is adopted where large stone quarries are readily accessible, in the form of rubble masonry with dressed stone on the face, as for instance at the Hull and Barry docks, and forms a very durable wall; but strong overhead staging carrying powerful gantries is necessary for laying large blocks. Brickwork has been often used where bricks are the ordinary building material of the district or can be made on the works, and requires only ordinary scaffolding; and harder or pressed bricks are employed for the facework. Concrete is very commonly resorted to now where sand and stones are readily procured; and where clean, sharp sand and gravel are found in thick layers in the excavations for a dock, as in the alluvial strata bordering the Thames, dock walls can be constructed cheaply and economically with concrete deposited within timber framing, dispensing with regular scaffolding and skilled labour. Such walls require to be given a facing of stronger concrete, or of blue bricks, as at Tilbury, to guard against abrasion by vessels, chains and ropes; and dock walls are commonly provided at the top with granite or other hard stone coping where the wear is greatest. The foundations for dock walls are excavated in a trench below dock-bottom, only lined with timbering where the faces of the trench cannot stand for a short time without support, and with sheet piling through very unstable silt or sand; and the trench is conveniently filled up solid with concrete, carried out in short lengths in untrustworthy ground. To reduce the amount of filling behind the wall, the excavation at the back above dock-bottom, preparatory for the trench, is given as steep a slope as practicable, supported sometimes towards the base by timbering and struts; but occasionally the wall is built within a timbered trench carried down to the required depth, before the excavation for the dock in front of it has been executed, as effected at Tilbury. The filling at the back is thus reduced to a minimum, and the lower portion of the excavation can be accomplished by dredging, if expedient, after the admission of the water, the dock wall in this way being exposed to the least possible pressure behind.
The walls of open basins are often constructed out of water precisely like dock walls, as in the case of the basins forming the Manchester, Bruges and Glasgow docks; and basin walls open to the tide, as at Glasgow and in the tidal basin outside Tilbury docks (fig. 7), differ only from dock walls in being exposed to variations in the pressure at the back resulting from the lowering of the water-level in front, which is, indeed, shared to some extent by the walls round closed docks where the difference in the high-water levels of springs and neaps is considerable. The walls, however, round basins in tideless seas, such as Marseilles, occasionally those inside harbours, and especially quay walls along rivers and round open basins alongside rivers, have to be constructed under water.
At Marseilles, the simple expedient was long ago adopted of constructing the quay walls lining the basins formed in the sea, by depositing tiers of large concrete blocks on a rubble foundation, one on top of the other, till theyOpen basin and river quay walls founded under water.reached sea-level, and then building a solid masonry quay wall out of water on the top up to quay-level, faced with ashlar (fig. 13), the wall being backed by rubble for some distance behind up to the water-level. The same system was employed for the quay walls at Trieste, and at Genoa and other Italian ports. A quay wall inside Marmagao harbour, on the west coast of India, was erected on a foundation layer of rubble by the sloping-block system, to provide against unequal settlement on the soft bottom (seeBreakwater). The quay walls alongside the river Liffey, and round the adjacent basins below Dublin, were erected under water by building rubble-concrete blocks of 360 tons on staging carried out into the water, from which they were lifted one by one by a powerful floating derrick, which conveyed the block to the site, and deposited it on a levelled bottom at low tide in a depth of 28 ft., raising the wall a little above low water. After a row of these blocks had been laid, and connected together by filling the grooves formed at the sides and the interstices between the blocks with concrete, a continuous masonry wall faced with ashlar was built on the top out of water. A quay wall was built up to a little above low water on a similar principle at Cork, with three smaller blocks as a foundation, in lengths of 8 ft. Cylindrical well foundations have been extensively used for the foundations of the quay walls along the Clyde, formerly made of brick, but subsequently of concrete, sunk through a considerable variety of alluvial strata, but mostly sand and gravel fully charged with water. Compressed air in bottomless caissons has been increasingly employed in recent years for carrying down the subaqueous foundations of river quay walls, through alluvial deposits, to a solid stratum. About 1880, a long line of river quays was commenced in front of Antwerp, extending in the central portion a considerable distance out into the Scheldt, with the object of regulating the width of the river simultaneously with the provision of deep quays for sea-going vessels; and the quay wall was erected, out of water, on the flat tops of a series of wrought-iron caissons, 82 ft. long and 29½ ft. wide, constructed on shore, floated out one by one to their site in the river between two barges, and gradually lowered as the wall was built up inside a plate-iron enclosure round the roof of the caisson, which was eventually sunk by aid of compressed air through the bed of the river to a compact stratum (fig. 14). The weight of the wall counteracted the tendency of the caisson and the enclosure above it to float; and the caisson, furnished with seven circular wrought-iron shafts, provided with air-locks at the top for the admission of men and materials and for the removal of the excavations, was gradually carried down by excavating inside the working chamber at the bottom, 6¼ ft. high, till a good foundation was reached. The working chamber was then filled with concrete through some of the shafts, the plate-iron sides of the upper enclosure were removed to be used for another length of wall, the shafts were drawn out and the hollows left by them filled with concrete, the apertures between adjacent lengths were closed at each face with wooden panels and filled with concrete, and a continuous quay wall was completed above. The most recent quay walls constructed in the old harbourat Genoa were founded under water on a rubble mound in a similar manner by the aid of compressed air (fig. 15). Quay walls also on the Clyde have been founded on caissons, consisting of a bottomless steel structure, surmounted by a brick superstructure having hollows filled with concrete, in lengths of 80 ft. and 27 ft., and widths of 18 ft. and 21 ft. respectively, carried down by means of compressed air from 54 to 70 ft. below quay-level, on the top of which a continuous wall of concrete, faced with brickwork, and having a granite coping, was built up from near low-water level (fig. 16). In many cases where soft strata extend to considerable depths, river quays and basin walls have been constructed by building a light quay wall upon a series of bearing and raking piles driven into, and if possible through, the soft alluvium. Thus the walls along the Seine, and round the basins at Rouen, were built upon bearing piles carried down through the alluvial bed of the river to the chalk. The lower portion of the quay wall was constructed of concrete faced with brickwork within water-tight timber caissons, resting upon the piles at a depth of 9¾ ft. below low water; and upon this a rubble wall faced with bricks was erected from low water to quay-level, backed by rubble stone laid on a timber flooring supported by piles, together with chalk, to form a quay right back to the top of the slope of the bank of the deepened river (fig. 17). The quay walls of the open basins bordering the Hudson river at New York have had, in certain parts, to be founded on bearing piles combined with raking piles, driven into a thick bed of soft silt where no firm stratum could be reached, and where, therefore, the weight could only be borne by the adherence of the long piles in the silt. Before driving the piles, however, the silt round the upper part of the piles and under the quay wall was consolidated by depositing small stones in a trench dredged to a depth of 30 ft. below low water; the piles were driven through these stones, and were further kept in place by a long toe of rubble stone in front and a backing of rubble stone behind carried nearly up to quay-level, behind which a light filling of ashes and earth was raised to quay-level. The slight quay wall resting upon the front rows of bearing piles was carried up under water by 70-ton concrete blocks deposited by means of a floating derrick; and the upper part of the wall was built of concrete faced with ashlar masonry (fig. 18). The basin and quay walls at Bremen, Bremerhaven and Hamburg were built on a series of bearing and raking piles driven down to a firm stratum, the wall being begun a few feet below low water. At Southampton, ferro-concrete piles were employed in constructing the deep quays; and a wharfing of timber pilework has been frequently used for river quays.
Where the increase of trade is moderate and the conditions of the traffic permit, and also at coal-shipping ports, economy in construction is obtained by giving sloping sides to a portion of a dock in place of dock walls, the slope being pitched where necessary with stone; and the length of the slope projecting into a dock is sometimes reduced by substituting sheet piling for the slope at the toe up to a certain height. By this arrangement jetties can be carried out across the slope as required, enabling vessels to lie against their ends; and coal-tips are very conveniently extended out across the slope at suitable intervals (fig. 8).
As dock walls, especially before the admission of water into the dock, constitute high retaining walls, not infrequently founded upon soft or slippery strata, and backed up with the excavated materials from alluvial beds, into which water is liable to percolate,Failures of dock walls.they are naturally exposed under unfavourable conditions to the danger of failure. A dock wall erected on unsatisfactory foundations is liable, where the bottom is soft, to settle down at its toe, owing to the pressure at the back, and to fall forwards into the dock, as occurred at Belfast; or where the silty bottom slips forward under the weight of the backing, the wall may follow the slip at the bottom and settle down at the back, falling to some extent backwards, as exemplified by the failure of the Empress basin wall at Southampton. The most common form, however, of failure is the sliding forwards of a dock wall, with little or no subsidence, on a silty or slippery stratum under the pressure imposed by the backing. Thus the Kidderpur dock walls furnish an instance of sliding forwards on muddy silt, and part of the South West India dock walls on two underlying, detached, slippery seams of London clay.
To avoid these failures with untrustworthy foundations, great care has to be exercised in selecting the best hard material available, unaffected by water, for the backing, which should be brought up in thin, horizontal layers carefully consolidated; and where there is a possibility of water accumulating at the back, pipes should be introduced at intervals near the bottom right through the wall in building it, and rubble stone deposited close to the back of the wall, so as to carry off any water from behind, these pipes being stopped up just before the water is let into the dock. These precautions, moreover, are assisted by reducing the amount of backing to a minimum in the construction of the wall, best effected by building the wall inside a timbered trench. The liability to slide forwards can be obviated by carrying down the foundations of the wall sufficiently below dock-bottom to provide an efficient buttress of earth in front of the wall, and also by making the base of the wall slope down towards the back, thereby forcing the wall in sliding forwards to mount the slope, or to push forward a larger mass of earth; whilst a row of sheet piling in front of the foundations offers a very effectual impediment to a forward movement, and, in combination with bearing piles, prevents settlement at the toe in soft ground. In very treacherous foundations it may be advisable to defer the completion of the backing till after the admission of the water; but the additional stability given to a retaining wall or reservoir dam by an ample batter in front, is precluded in dock walls by the modern requirements of vessels.
Silt accumulates in docks where the lowering of the water-level by locking, the drawing down of half-tide basins, and the raising of the water at spring tides, involve the admission of considerable volumes of tidal water heavily charged with silt, which is deposited in still water and has to be periodicallyMaintenance of depth.removed by dredging. To avoid this, the water is sometimes replenished from some clear inland source, an arrangement adopted at some of the South Wales ports opening into the muddy Severn estuary, and at the Alexandra dock, Hull, to exclude the silty waters of the Humber. At the Kidderpur docks on the Húgli, the water from the river for replenishing the docks is conducted by a circuitous canal, in which it deposits its burden of silt before it is pumped into the docks.
In order to deal expeditiously with the cargoes and goods brought into and despatched from docks, numerous sidings communicating with the railways of the district are arranged along the quays, which are also providedEquipment on quays.with steam, hydraulic or electric travelling cranes at intervals alongside the docks, basins or river, for discharging or loading vessels, and with sheds and warehouses for the storage of merchandise, &c., the arrangements depending largely upon the special trade of the port. Though different sources of power are sometimes made use of at different parts of the same port, as for example at Hamburg, where the numerous cranes are worked by steam, hydraulic power or most recently by electricity, and a few by gas engines, it is generally most convenient to work the various installations by one form of power from a central station. Water-pressure has been very commonly usedas the motive power at docks, being generated by a steam-engine and stored up by one or more accumulators, from which the water is transmitted under pressure through strong cast-iron pipes to the hydraulic engines which actuate the cranes, lifts, coal-tips, capstans, swing-bridges and gate machinery throughout the docks (seePower Transmission:Hydraulic). The intermittent working of the machinery in docks results in a considerable variation in the power needed at different times; but economical working is secured by arranging that when the accumulators are full, steam is automatically shut off from the pumping engines, but is supplied again as soon as water is drawn off. Electricity affords another means for the economical transmission of power to a distance suited for intermittent working; as far back as 1902 it was being adopted at Hamburg as the source of power for the machinery of the extensive additional basins then recently opened for traffic.
At ports where the principal trade is the export of coal from neighbouring collieries, special provision has to be made for its rapid shipment. Coal-tips, accordingly, are erected at the sides of the dock in these ports, with sidings onCoal-tips.the quays at the back for receiving the trains of coal trucks, from which two lines of way diverge to each coal-tip, one serving for the conveyance of the full wagons one by one to the tip, after passing over a weigh-bridge, and the other for the return of the empty wagons to the siding where the empty train is made up for returning to the colliery (fig. 8). Each full wagon is either run at a low level upon a cradle at the tip, then raised on the cradle within a wrought-iron lattice tower to a suitable height, and lastly, tipped up at the back for discharging the coal; or it is brought along a high-level road on to a cradle raised to this level on the tower, and tipped up at this or some slightly modified level. The coal is discharged down an adjustable iron shoot, gradually narrowed so as to check the fall; and on first discharging into the hold of a vessel, an anti-breakage box is suspended below the mouth of the shoot. When full, this is lowered to the bottom of the hold and emptied, thereby gradually forming a cone of coal upon which the coal can be discharged directly from the shoot without danger of breakage. Other contrivances are also adopted with the same object.