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THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



319 



series of drawings, containing the plans and sections of existing breakwaters 

 and piers, showing the injur)' sustained from storms, accompanied the same. 

 Colonel Jones explained liy the various sections of breakwaters shown in 

 the drawings, the changes of form, and the additions to their cubic content 

 which had been made at different periods, In consequence of the violent 

 action of storms. 



The Plymouth Breakwater has had its form altered three times ; each time 

 the base has been extended, and the sectional area increased. 



At the Hosvth Pier the sections showed three distinct forms assumed by 

 the mass of materials, in consequence of the varied action of the waves. 

 The damage done is now so extensive, that the sea threatens to make a clear 

 breach through the works. 



The sections of the Kingstown Pier showed the original form to have been 

 a slope of 4 to 1 and 5 to 1, covered with heavy pitching, wliich had been 

 repeatedly torn up, and some of the stones weighing 10 tons were carried 

 to considerable distances : an external mole of rough work containing nearly 

 200,000 tons of stone which had been deposited upon the foreshore was 

 almost all washed away ; while the toe of the work beneath low-water mark, 

 although at a greater angle than the other parts, remained undisturbed. 



.\t Dunmore Harbour, although the long glacis with a slope of 5 to 1 is 

 protected by pitching composed of square stones of from 2 J to 6 tons weiglit, 

 and above .t;i2,000 has been expended, it has received very extensive damage. 

 Many otlier cases of injury to sloped works were mentioned, and it was 

 stated, that from these examples, coupled with observations upon some 

 ancient piers in Cornwall and other exposed situations, wbicli, although b\iilt 

 of rough materials and with a nearly vertical sea face, had resisted the action 

 of heavy seas, the Shannon Commissioners had determined to iry, at Kilrush, 

 a sea wall with a very sliglit inclination, and up to the present time it had 

 sustained no injury, although previously the sloped work had been destroyed. 

 Colonel Jones, being convinced of the superiority of this form, had de- 

 voted much time to observations of the action of the waves upon works of 

 all kinds, as well as to the various modes of using the materials composing 

 the sea-walls ; and he felt assured that if the stones were of an average size, 

 square-jointed, and well laid, even without cement, forming an almost vertical 

 wall of moderate thickness, springing from a point as much below low-water 

 mark as could he conveniently attained, the work would be more durable. 

 "Beton" (concrete) was now much used in France for the construotion of 

 sea defences : it was generally done by building caissons of ashlar, filling 

 them in solid with " Beton," and then caulking all the ashlar joints with 

 oakum : this kind of work was very durable. 



In answer to a remark by General Pasley, Colonel Jones believed that the 

 greatest injury was done by the receding waves, particularly if the joints of 

 the work were not well closed. 



Remarks. — Jlr. Itennie took a hasty review of the moles and breakwaters 

 mentioned by the early writers, as being thrown out for the purpose of 

 forming harbours; Vitruvius particularly described, among other similar 

 works, a mole constructed with a kind of concrete composed of pozzuolana. 

 Mr. Rennie contended that engineers were not in error in taking as their 

 guide the natural inclination of the sea shore opposite the situation where 

 the breakwater was intended to be placed. It would be found, in following 

 the coast of England from the perpendicular primitive clitfs of Cornwall to 

 the flat shingle beach of Norfolk, between which places is found almost every 

 variety of geological formation, that the profile of the sea shore differed 

 according to the material of which it was composed and the peculiar action 

 of the sea upon it from local circumstances. It had been shown tliat the 

 force of the waves acted more prejudicially upon the point above low-water 

 than below it ; that the work would stand at a great inclination at the latter 

 point, indeed that it was rarely injured even when all above it was carried 

 away ; that if the water was deep, the action of the waves would extend 

 deeper : all these and many other points required to be considered in fixing 

 upon the slope for any sea-wall ; and therefore he could not accord with 

 Colonel Jones's views in adopting an arbitrary form for all situations, without 

 considering the exigencies of peculiar localities. He ha<l been particularlv 

 struck with the regularity of the slope assumed by the materials at the Kings'- 

 town pier after a storm ; hut in that and all similar positions, the inclination 

 of the face varied with circumstances, and with the degree of violence of the 

 action of the waves. Amoug the many arguments against the proposed 

 perpendicular form, might be mentioned the increased expense; for if built 

 of squared stones below low-water mark, tlie work must he done from a 

 diving-hell ; and also that the form is objectionable for a pier, as the wave 

 is thrown up in a mass, instead of expending its force in rolling over the long 

 slope of the fore-shore. Mr. Telford had abandoned vertical sea-walls on 

 these and other accounts. 



Mr. Vignoles agreed to a certain extent (but not fully) with the form pro- 

 posed by Colonel Jones ; he believed that although the construction might 

 be rather more costly, it would be amply compensated for bv the greater 

 durability ; and he saw no diflicnlty in doing the work. The proposed plan 

 he understood to be by commencing the foot of the wall only at snch a depth 

 below low-water as should prevent the violent action of tlie waves upon it. 

 At Ardglass the upper portion only of the pier is destroved ; al! that part 

 below low-water remains perfectly sound : it is of ashlar of large dimensions, 

 placed from a bell. 



Mr. Gordon had seen sections of the works which were commenced for 

 forming a breakwater at .Madras : the materials reached at the highest point 

 to within about 10 ft. of low-water, and amidst the violence of the surf of 

 that coast the work stood undisturbed at an angle of 45° : it was composed 



of " pierre perdue." At Algiers the French engineers had used extensively 

 masses of concrete (blocs de beton), but at first they were displaced and 

 destroyed by the force of the seas ; the cubic capacity of the masses had 

 however been increased to the extent of 2 metres square by 3 metres long ; 

 they were floated out, and allowed to drop into their places from slings ; and 

 now they succeeded perfectly. The upper part of the work is intended to 

 be of concrete cast in caissons, the section below low-water is at an angle 

 of 45", and above it like an ordinary quay wall with a curved "batter." 



Sir John Kobison, in allusion to the depth of the wave and the power of 

 its action at .Madras, said that, during a violent storm, a quantity of pigs of 

 lead had been cast ashore near the fort, and it was proved tha't they had 

 come from a vessel which had been wrecked at more than a mile from the 

 shore, dnring the siege by La Bourdonnaye. 



The President observed that at the Plymouth Breakwater the largest blocks 

 (some of them weighing from to 8 tons) and the greatest number have 

 been washed from the sea face over into the Sound ; the square stones with 

 which the fore shore is paved are placed with the utmost care, and Uttle 

 comparative injury has been done since that method has been adopted. 

 Engineers now generally recommend a deep paving of squared stone in bond 

 courses, as the best mode of construction. In order to insure tlie stability 

 of the lighthouse now erecting at the extremity of the Plymouth Breakwater, 

 a foundation of squared stones has been carried up from the natural rock, 

 and an inverted arch turned below the level of the top of the work ; and, 

 for its farther security, a buttress is now throv™ out upon the foot of the 

 south slope, in order to prevent the stones from being carried away. It is 

 evident, that if the materials are deposited at an inclination, any porti»'' 

 being displaced is only carried down to where, although strictly speaking 

 may not be wanted, it must nevertheless assist in consohdatin'g the mass ; 

 and the vacant spaces can easily be fliled up. Under similar circumstances 

 a perpendicular wall would sutler more severely, and probably would have 

 fallen entirely. He therefore considered that in situations like that of the 

 Plymouth Breakwater, which was exposed to a heavier sea than Cherbourg, a 

 long slope for the sea face was essential. Still there were situations where 

 the form proposed by Colonel Jones would no doubt be available, and the 

 members were much indebted to him for the suggestion, as also for the 

 valuable observations shown in the sections accompanying the paper: he 

 hoped that be would continue them, and that other members, who had equal 

 opportunities and less arduous duties to perform than the author, would give 

 the Institution the benefit of their observations. 



Mr. Macneill had seen at the mouth of the Ilelder, in North Holland, 

 banks nearly vertical, constructed of sea-weed and hazel-wood fascines, 

 backed with clay: they were exposed to a very hea\7 sea, and yet stood 

 extremely well — there was considerable elasticity in them, for when a wave 

 struck them, the vibration was felt at a distance along the bank. In other 

 situations on the coast of Holland, the sea-banks are long slopes of sand at 

 an inclination of 10 to 1, thatched with straw. In many places groins were 

 built to break the length of the wave, and diminish its force ; he had adopted 

 similar groins, and found them answer perfectly. 



Mr. H. R. Palmer observed that the form suggested by Colonel Jones for 

 the faces of breakwaters did not appear sufiiciently justified by observed 

 facts ; the idea was entirely of a speculative character, and was contrary to 

 the law of nature, which should be the engineer's chief guide. Manv years 

 ago Mr. Palmer had occasion to study very carefully the motion of the shingle 

 beach at the harbour of Folkstone, and at several other places, and the results 

 of his observations were published in the Transactions of the Royal Society. 

 He found that the slopes of the surface were always regulated by the force 

 of the waves, and the angle at which they impinged ; and that when the 

 forces were at right angles with the line of beach the whole of the pebbles 

 were brought down below the level of the acting forces. ,\t Folkstone, 

 when the sand was thus left bare, the surface stood at an angle of 9 to 1, 

 and that slope resisted the force of very heavy seas. The effect of the action 

 of the sea upon an upright surface was observable in every clifl" upon the 

 coast, and the tendency to destruction was everj'where obvious. Shingle 

 beaches might be considered as adjustable barriers, but in the construction 

 of piers it was necessary to adopt some jirecise form. When circumstances 

 required the walls to be nearly vertical, the line of their direction should be 

 determined with reference to the prevailing winds. Tliose portions of the 

 piers of Swansea harbour which formed even only a small angle with the 

 prevalent winds remained firm and substantial, but that part which was 

 directly opposed, or at right angles to them, has been undermined. la a 

 design of his for a pier in .Mount's Bay at Penzance, Mr. Palmer had so 

 arranged that the angle of the main pier should be at 5° with the line of 

 the greatest forces. Thus, then, a horizontal slope is in fact made as a sub- 

 stitute for a rising one. He attributed the failures alluded to by Colonel Jones 

 more to defective workmanship than to faults in the principle of the struc- 

 ture. — Mr. Palmer exhibited and presented to the Institution jilans of 

 Kamsgatc, Dover, Folkstone, Swansea, and Penzance harbours. 



General Pasley, in his observations of the action of the sea upon various 

 parts of the coast, liad remarked that the slope of the beach was exactly in 

 accordance with the materials of which it was composed: if it was shingle 

 or decomposed rock or soft material, the slope was gradual ; but if the shore 

 was rocky, the waves had not any serious effect upon the bluff face opposed 

 to them, except in the case of chalk cliffs. He conceived, therefore, that a 

 perpendicular w.ill constructed of large ashlar work well cemented, would 

 assume the character of a rock, and all the prejudicial action of the receding 

 wave would be avoided. 



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