18 10. J 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



2G5 



SEA WALLS. 



Account of the Effect of the Storm, of the 6th of December, 1847, on 

 four Sea Walts, or Biihcarks, of different forms, on the coast near 

 Edinburgh; as illnstratint) the principles of the construction of Sea 

 Befen^ses. By William John Macquobn Ranktne, A. Inst. C.E. 

 — (Paper read at the Institution of Civil Enj^ineers.) 



There are few branches of engineering: with respect to which 

 greater uncertainty and difference of opinion exist, than that of 

 the construction of sea walls and breakwaters. The question has 

 been frequently before tlie Institution, and in its archives there is 

 much useful information on the subject. The valuable paper of 

 Lieutenant Colonel H. D. Jones, read in IS+S,' may be particu- 

 referred to, as its conclusions are to a certain extent verified by 

 the facts which have come under the author's observation. Con- 

 ceiving that every addition, however small, to the facts recorded 

 respecting the efficiency of such works, must tend to bring the 

 principles of their construction nearer to cei'tainty, the author 

 felt it to be his duty to lay before the Institution, transverse 

 sections of four sea walls, upon a portion of the coast of the Frith 

 of Forth, near Edinburgh, having an exposure towards the north 

 and north-east, and to give an account of the effect upon them of 

 one of the most violent storms on record in this climate, which 

 took place on the 6th of December, 1847. 



Fig. 1. — Edinburgh and Dalkeith Eailway, Leith Branch. Sec- 

 tion of the Sea \\ all, original design by Messrs. Walker and 

 Surges. — A, Level of High Water Spring Tides. 



Figs. 1, and 2, represent the sea wall of the 

 Leith branch of the Edinburgh and Dalkeith 

 '■^ railway, which was completed in the winter of 



1837. Fig. 1 is the ti'ansverse section, as originally designed by 

 the consulting engineer, Mr. Walker. Fig. 2 is the transveTse 

 section, as the wall was actually built. 



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^o£ 



Scale of Feet, Figs. 1 and ■>. 

 Fig. 2.— Edinburgh and Dalkeith Railivay, Leith Branch. Section of the Sea Wall as 

 executed in 1837.— A, Level of High Watsr Spring Tides ; B, Ballast: C, C, C, Concrete; 

 U, Sand ; E, Dowel. 



» See 'Journal,' lti41'. Vol V., p. 318. 



The author was resident engineer of the railway whilst this wall 

 was e.xecuted, and it is the only one of the four walls the for- 

 mation of which he can describe from actual inspection during 

 the progress of the work; the other three sections are, therefore, 

 to be regarded rather as giving the external foi'm, and the general 

 style of building of the walls they refer to, than as affording 

 minutely accurate information respecting the details of their con- 

 struction. 



The deviations from the original design and specification were 

 chiefly in matters of detail, and will be apparent on an examina- 

 tion of the two sections. The most important were the fol- 

 lowing:— 



The hearting was composed of concrete, instead of rubble. The 

 parapet was omitted, as no bulwark of ordinary height could have 

 kept off the spray, which sometimes rises 20 feet above the wall. 

 A small wall was added at the landward side of the embankment, 

 so as to retain the sand in a sort of trough ; for, until this wan 

 done, it was found that the spray, collecting in pools on the 

 surface of the embankment, after a gale, washed away the material 

 in large quantities; but after the formation of tlie trougli, the 

 water subsided by filtration through the sand, without doing any 

 damage As boulder stones were abundant on a neiglibouring 

 part of the beach, they were used to form a nearly horizontal 

 pitching to secure the foundation against being undei'inined, in- 

 stead of using the sheet piling shown in the section, fig. 1. 



It was found, from the effects of a violent gale which took place 

 during the progress of the work, that the coping stones, which 

 weighed about half-a-ton each, were liable to be lifted by the sea, 

 thus exposing to destruction the courses of smaller stones beneath 

 them. They were therefore connected together by cylindrical 

 cast-iron dowels, l| inches in diameter, and 12 inches long, placed 

 in the line of the centre of gravity of the stones, and penetrating 

 •6 inches deep into holes made to fit them, in each stone. This 

 mode of connection has answered its purpose perfectly, not a 

 single coping stone having been lifted by the most violent storms. 

 With the exception of the alterations and additions just men- 

 tioned, the wall was e.xeeuted almost exactly according to the 

 original design of the consulting engineer. 



The total length of the wall is about 750 yards, and its height is 

 13g feet above the beach at the most exposed part, diminishing to 

 about 6 feet at the ends; this gives only 4 feet above the level of 

 high water of equinoctial spring tides. The least thickness is 

 5 feet, the greatest thickness is 10 feet; the back of the wall is 

 vertical; the face has a batter of about 5 inches in a foot, at the 

 lower part, and towards the upper part it becomes curved, and 

 overhangs slightly at the top. 



The whole of the masonry is of white sandstone from Craigleith, 

 quarry. The foundation course is composed of large flat stones, 

 12 inches tliick, laid horizontally, at an average depth of 4 feet 

 below the surface of the beach. Tlie stratum on which it rests is 

 clean sea sand, with a slight mixture of fine gravel; firm when 

 the tide is low, but when saturated with water, it is so moveable 

 that the author has found stakes, which had been driven 2 feet 

 deep into the beach to mark the line, shifted during a stormy 

 night 3 feet from their former place, without losing their vertical 

 position, or rising out of the sand; yet the foundation of the wall 

 has never shown the slightest symptom of insecurity. Tliis is 

 one amongst many instances of the safety of a foundation on pure 

 sand when it has no outlet to escape laterally. 



The face of the wall was built in courses, from 6 inches to 

 12 inches in thickness, of squared hammer-dressed stones, averag- 

 ing 2 feet in depth; the back was built of coursed rubble, averag- 

 ing about 18 inches in depth, and the interior was filled with con- 

 crete, composed of gravel from the beach, laid in courses 12 inches 

 in thickness, as the masonry was finished. There are two courses 

 of bond stones as shown in the section. The coping stones are 

 14 inches thick, and average 3 feet in length. 



At first, the joints of the face were protected by scraping out 

 the mortar for a depth of 2 inches, and pointing them with 

 cement; but as it was found that the sea sometimes broke off and 

 extracted large pieces of the cement, even after it had set, it was 

 considered advisable to lay the remainder of the face stones in 

 cement, for a depth of 4 inches inwards, whilst building the wall. 



In order to promote the accumulation of sand and gravel at the 

 base of the wall, several timber groynes, formed of planks set on 

 edge between a double row of piles, were placed at right angles 

 to it. 



The whole of the masonry was constructed by workmen in the 

 employment of the company, under the immediate direction tf 

 Mv. Somerville, upon whom the style of execution reflects great 

 credit. 



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