lS-17.] 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



W53 



lireali wafers may either prove lliat the slopes were not sufiicienlly great, 

 or tliat the njatetials composini; Ihein have been ill assf nil)ie(l, so as to 

 cause vacuities h'lvveen (he stones, or, «hich is perliaps the most common 

 cause of failure, liie foundation of tlie glacis has not been laid at a low 

 enoujjh level, or, liually, that tliey have not been paved with stones of suf- 

 licient weight, nor united to each other with the care necessary to 

 exclude the action of tiie \iater, which tends to I'eraove this description uf 

 paving. 



Tlie anaIof;y between the natural beach composed of loose materials and 

 the face of a breakwater is not complete, because the materials with which 

 a breakwater is to be pa\ed may not only be lartjer than tho^e which play 

 about on a natural shore, but may have the atldilioiial advantaj;e of beiu{:j 

 carefully assembled and united together. Again, it must be remarked 

 that arlilicihl works are exposed to greater risk from casualties than the 

 natural beaches, from the following reasons: First, l)ecanse the choice of 

 their position is too often empirical in so far as their stabddy is conci rued, 

 and is primarily and sometimes almost solely determined, with reference 

 t'l their Illness to produce an efTect in stilling a basin or harbour, with only 

 a sec"udary repard to the risks of injury which they may eucouriter. And, 

 second, because, from motives of economy, such artificial works, so far 

 from having slopes greater than those of the neighb urin^ beaches, are 

 generally sleeper^aml, as before noticed, are too olten delicient in solidity 

 and in the careful protection of their surface by means t>f pitching. 

 - From the general tenor of the answers you have given to Sir Howard 

 Douglas's questions, \ou are of opinion that the unbroken wave has per- 

 cussive force like the broken wave, and that, of the two, you consider the 

 unbroken wave to have tlii.i force in a greater degree than the brokeu 

 waie; will 50U be good enough to stale how you account, therefore, for 

 these facts on your theory ? — I am of opinion that an unbioken wave has 

 percussive force like a broken wave, and probably in a greater degree, 

 because it has not sustained the same check or retardation. I believe that 

 all waves, except the great tide wave, have an onward motion, because I 

 know of no cause constantly in operation which is capable of producing 

 waves but the wind, and this agent, it appears to me, must of necessity 

 impress upon the waves .'onie degree of onward ipotion. From all my 

 experience I have invariably found that the sea broke gently and playfully 

 on all the slaping walls, while it broke with a loud noise on the plumb 

 walls, and raised the spray in some cases to the height of 30 feet and up- 

 wards. In striking against this perpendicular face the successive waves 

 make a soun<l similar to that of a great gun at a distance, carrying some- 

 times with them large pieces of stone which, falling on a lighthouse roof, 

 occasionally damage it ; though at the distance of 240 yards from the face 

 of the rock. 



There is no analogy between the case of a pile which permits the sea to 

 pass round it freely, and Ihat of a continuous wall which checks its pro- 

 gress and opposes a long front of lesistance. The mere circumstance of 

 the in-shore piles being more injoi-ed than the outer ones, appeals to me 

 not very relevant to the sulject under consideration. 



As to the circumstance of the piles which were braced being more in- 

 jured than those which were unbraced, this only proves that from the 

 manner in which the braces Wf re ajiplied, they offered more resistance to 

 tbe wave than was compensated for by the additional support derived from 

 them. I have sufficiently shown that it is possible to explaiu the various 

 circumstances adduced by Colonel Alderson ou the vit w which I have 

 taken of the percussive nature of all waves with which we have to do in 

 the formation of breakwaters. 



In my own mind I have no doubt that ocean waves are not purely 

 oscillatory, but that all waves liave an onward motion, and possess per- 

 cussive force, and my bumble conviction is, lhat the first attempt on a large 

 scale to check the force of the waves in deep water, by means of a verti- 

 cal wall, will prove a signal failure, and lhat a force will be developed by 

 the collision of the wave with the wall, whose amount will he found to 

 surpass anything which has hitherto beeu experienced on the face of a 

 sloping breakwater. 



I cannot look upon the works at Plymouth, Kingstown, and Cherbourg, 

 eacli of which I have visited, as any longer merely experimental. 8uch 

 works, may, on the whole, he considered as satisfactory as the nature of 

 the circumstances will permit. 



Do you think it impossible to construct a breakwater at Dover in such 

 a maumr, and by sucii methods, as would give it practically a monolithic 

 character, and render it capable of resisting the force of the sea in the 

 same manner as an upright cliff? — I have already expressed my belief 

 that the waves have an onward motion, and that this motion would be cou- 

 linued until checked and thrown back by the action of the wall. The 

 wall therefore must reverse the movement and annihilate the force on its 

 onward course, and seems consequently obnoxious to sustain the final effort 

 of the waves. I cannot see bow in such a case any part of tlie water can 

 he considered as at rest, and thus operating as a non-conductor of the 

 force ; and the facts alluded to in my former answers, wliich I have myself 

 observed, as to the action of waves against cblTs, seem fully to corroborate 

 my views. 



Annlx (F). — Mr. M'lLLIAM ST:v\r.T, Superintendent of the Plymouth 



Breakwaler, o'l the Mode of Construction 

 I have been employed at tbe breakwater from the commencement of the 

 work in 1811 ; but as superintendent only since 1829. 



The slope, as left by tbe sea, from low water upwards, was about 5 feet 

 horizontal to 1 foot perpendicular, ai;d iu some pi ces rather m< re. 



Messrs. Chapman, .lessop, and Rennie (the late ?>rr. John Kennie), engi- 

 neers, were called in to report ; and it was thereupon determined, in April 

 IH-'5. that a breakwater should be formed regularly from the level of low- 

 W'ater spring-tides, vvitii a casing of rough squared blocks of granite ami 

 linicslone, commencing ou the exterior, or south slope, with a slope of H to 

 1, as the sea had left it; and on the inner, or north side, wiih a slope of 

 2 to 1. 



What was the object of increasing the breadth at the top? — To add to 

 the stability of the breakwater. 



Do you attribute the damages you have stated in the years alluded to, 

 to the form and shape of the breakwater, and to the want of tilling up the 

 interstices? — In the first gales I attributed the damages to the fact that 

 we had not length enough of foreshore, or of extension to seaward. 



Not slope eiimigh ? — Not slope enough. 



What was the objection you hail to the more upright slope? — I was con- 

 vinced it could not stand ; and my belief v\as afterwards confirnied by the 

 actual failure of a solid part of the breakwater, which had been built on 

 this plan, and also by the failure of a part of Statten Pier itself, 

 which had never to encounter anything like to severe a test as the break- 

 water. 



Do you think if the breakwater had been constructed in any other form, 

 for instance, if it had been either wholly opiight from the bottom of the 

 sea, or upright from about low-water mark, lhat siiih a breakwater would 

 have had power to resist the force of the sea which overturned that large 

 portion of it which you have nn-niioned ? — I think not. 



Do yon think that olilique planes of breakwaters, built in the sea are 

 better calculated to resist the force of the sea in the direction of motion 

 than any upright work? — I do, decidedly. 



Having said you prefer a sloping breakwater, as best able to resist the 

 force of the sea, 5011 further state, from your own experience, you think 

 the long slope of 5 to 1 is that which is most likely to remain in a state of 

 stability ?— I do. 



I would begin by throvTing in stones and getting the whole up to low- 

 water mark, letting them find their own base in the first instance, wiih 

 rubble stone, large and small together, and theu lhat would become a pro- 

 tection, and the sea would level down and you could then add to it 

 a^ain. 



Was any part of it ever made upright ?— Never. 



So that the upright building was never tried ? — Never. 



Arvsix (G). — Mr. J. M. Rendcl, on the Mode oj Construction, and 



Evidence, 

 To construct a breakvTater in seven fathoms water is, I apprehend, a 

 very formidable undertaking, especially if any of the ingenious contriv- 

 ances of caissons and machines of that kind are to be resorted to. I doubt 

 very much, if a breakwater is to be constructed in seven fathoms water, 

 whether the only safe plan would not be to deposit in the usual way from 

 vessels (if it is a detached breakwater, or f. om a railway, if it is a break- 

 water connected with the shore, and the shore produces suitable male- 

 rials), a mass of stone up to within, say, two or three feet of low water; 

 and aliove that to construct perpendicular walls of the kind referred to in 

 Col, Jones's letter of sugge.-tions. 



Considerable doubt being entertained as lo the slopes, and particularly 

 the seaslope of a breakwater, as least likely to be damaged by the action 

 of the waves, you are lequested to stale, on reading Col. Jones's paper 

 upon this important subject, your opinion upon it? — I think Col. Jones 

 would be very likely to fall into tbe same error in universally applying 

 perpendicularly sided breakwaters as other engineers have been of unF- 

 versally employing sloping ones. I think if the stones were thrown in acJ 

 allowed to form their own slope, that slope being determined by the nature 

 of the materials up to within two or three feet of low water, and then the 

 breakwater raised upon that with perpendicular sides, it would be the 

 most economical plan in most situations. I should be more disposed, if I 

 bad to build one in seven fathoms water, to adopt the plau I before referred 

 to: suppose I had an unlimited command of materials, I should first of all 

 begin to deposit those materials to form a rough mass up to within a mode- 

 rate depth at low water, and then when I had brought my foundations up 

 to that point at which the sea would begin to attack me, 1 should begin to 

 attack the sea by building wiih a cla-s of materials that would be its mas- 

 ter. I thiuk an upright wall in that case might be desirable. 



In your evidence before the Commissioners last year on the difTicully of 

 constructing works in seven fathoms of water, you deprecate the use of 

 caissons, and expressed doubts whether a breakwater could be con- 

 structed in seven fathoms water by such means ; do you retain that 

 opinion ?— I do. 



Vou say you do not know of any instance in which a breakwater, with 

 au upright face of the magnitude now contemplated, has been constructed 

 in the open sea, in seven fathoms water ?— I du not. 



Theu you say in another part, that if you bad an unlimited command '.f 

 materials, you would begin to deposit those materials so as to form a rough 

 mass, with a slope up to about low--.vater mark, and upon that vou 

 would build a superstructure in the shape of an upright wall?— I should 

 do so. 



And you recommended this combination of the slope for the substructure 

 with an upright wall for the superstructure?—! should so build if I had 

 suiialjle uiateri.tls at hand. 



Are you still of that opinion ? — I am. 



You stated that if you bad plenty of materials at your disposal you 



