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THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



203 



suited in the year 1773 by the Grand Canal Company on the exten- 

 sion of their canal, fell into a grave error in advisinfr "To avoid 

 boffs if possible, but of all this going deeply into them," (Smeaton's 

 Reports, Vol. XL, p. 267.) In our time we are tauglit by e.xperi- 

 ence to inculcate contrary doctrine. 



Bog lands are, in our opinion, particularly favourable to canal 

 extension; the site of the canal is purchaseable at a low rate, it is 

 cheap and facile in execution — -always presuming that the line is 

 judiciously chosen and skilfully worked; it is perfectly retentive; 

 does not gutter the slopes at the water's edge as in clay and gravel 

 banks; and the elasticity of the towing paths is such, that they 

 continue for years without repair if used exclusively as trackways. 

 Moreover, a line of canal passing through bog furnishes the means 

 of reclamation on an extensive scale, as well in the preliminary 

 process of draining as in the conveyance of manure for its cultiva- 

 tion. The increase of fuel, and the employment which its manu- 

 facture would afford to the working classes in its vicinity, are 

 great inducements to give a decided preference to bog lands for 

 the site of a canal, — of course, other requirements being suit- 

 able. 



We are not surprised at Smeaton's advice to avoid bogs if pos- 

 sible, seeing the principle advocated by him of not going deeply 

 into them. The canal from the Forth to the Clyde, 35 miles in 

 length, passing partly through bog, was commenced by this cele- 

 brated engineer in 17()S, and was not finished until 1790, having 

 cost the large sum of 2^0,000/. 



Bogs do not constitute tlie master difficulty of canal making, as 

 is sufficiently attested by the history of tlie great undertakings of 

 that description. The canal of Languedoc required the great 

 genius of Vauban, and the munilicence of Louis tlie Fourteenth, 

 to carry it through its difficulties. Peter the Great was obliged 

 to abandon the projected canal from tlie Don to the Wolga after 

 a very large sum had been expended on it, owing to the unskilful 

 laying out of tlie line. These examples, which might be multi- 

 plied, will suffice for our purpose. 



That portion of the Grand Canal passing near the town of 

 Edenderry, in the King's County, furnishes a two-fold instance of 

 the difficulty of making a canal through bog, where the level of 

 the substratum is below that of the adjacent river, and of the ill 

 effects of not going deeply into the bog. It was supposed that the 

 level chosen, which afforded from 6 to 9 feet deptli of cutting, was 

 such as would enable the undertaking to be completed at the least 

 possible expense, assuming that the depth of cutting (allowance 

 being made for subsidence), would give a finished canal of the re- 

 quired dimensions — namely, 24 feet width of bottom, -t6 feet wide 

 at top, and 8 feet in height from bottom of canal to upper surface 

 of trackway. The excavation and drainage were carried on con- 

 currently, and that which ivas expected to be an unusually cheap 

 reach of canal in shallow cutting, ended, after several years of un- 

 remitting labour and enormous expense, in the formation of a 

 bank on either side, 45 feet high for a distance of 80 perches, so 

 that the canal with the carrying up of its sides and bottom to the 

 required level, containing 6 feet of water, was in the centre of a 

 high artificial embankment, having a base of fully 400 feet. In- 

 . deed the difficulties were so great, that it was more than once 

 contemplated to abandon the line, and to make a new cut; but 

 through the influence of the proprietor of the town of Edenderry, 

 an example has been furnished, for the benefit of the engineering 

 world at least, of an error of the gravest character having been 

 carried to a successful termination. 



Tlie following process was adopted in making this canal. Parallel 

 drains, at 10 perches from the centre line on either side, were 

 made, and at 2 perches distant from these, and from each otlier, a 

 series of parallel drains, to the extent of 34 perclies from the 

 centre line on either side, were then made, embracing a breadth 

 of 68 perches; these were crossed at riglit angles, at 2 perches 

 distant from each other, so that the area of the bog, from the 

 10-perch drain to the 34-perch drain, on either side of the em- 

 bankment, was divided into squares or ramparts of 4 perches area 

 each. Tlie drains of those squares were continually widened and 

 sunk, and the spoil thrown on the ramparts. When the spoil be- 

 came dry it was wheeled, together with an 18-inch lift of the ram- 

 parts, into the embankment in which the material was firmly tram- 

 pled and chopped, and while all the dry ramparts were so disposed 

 of a new set were being similarly prepared by sinking the drains. 

 The formation of the canal thus proceeded until the navigation 

 was opened. Great quantities of clay were then boated for the 

 lining of the bottom and sides, soling the trackways, and covering 

 the whole surface of the banks, as well to give weight and strength, 

 as to secure them against fire and waste in summer. The material 

 being dry and light, the surface was set on fire many times, and 



was liable for the same reason to be carried avvay by the winds; 

 the banks were, however, perfectly retentive. 



Previously to the opening, when the water had been let in tem- 

 porarily, a breach occurred, the reconstruction of which (we had 

 the direction of it) cost 10,000/. in securing the embankment. 

 Tliis was done by wheeling dry bog material into the broach, 

 firmly ramming it into its place, and incorporating it thoroughly 

 with the broken sides. Forty years ha\e elapsed since this was 

 made good, and no similar disaster has since occurred. 



Piling has sometimes been had recourse to in making up such 

 breaches; but it is a great mistake to drive piles in a bog embank- 

 ment, as they disunite the particles, and open a way for the water 

 to escape, thus increasing the evil they were intended to remedy. 

 Vallancey in his work on canals bears testimony to this fact, and 

 his views were derived from high, authorities, such as Castellus, 

 Belidor, and others. 



It is necessary to observe that the Edenderry Canal was made 

 through the centre of a deep basin; the lowest tap practicable 

 being 15 feet above the adjacent river, the Boyne. It is therefore 

 obvious that an improper site was chosen. 



We thus see the necessity of ascertaining in the first instance 

 the depths of the bog, the level and nature of the substratum; 

 and it may be laid down as a general rule that shallow cuttings 

 and embankments in deep wet bogs are to be avoided; that the 

 level at which marl is found, or near it, ought not be selected for 

 the bottom of a canal; and that perfect drainage should be carried 

 to such an extent and depth, as to give stability to an area ade- 

 quate to the sustainment of a secure navigation. 



At the desire of the Institute we shall give a brief account of 

 our process of making a canal through deep soft bog, for whicli 

 purpose we shall make choice of the Ballinasloe Canal, the most 

 recently, and we may be permitted to say, skilfully executed, from 

 the experience previously acquired, and the most difficult of any 

 in which we have been engaged, with the exception of that of 

 Edenderry. Before our time, the Grand Canal was carried 

 through three short reaches of bog in the county of Kildare with 

 great difficulty; the water was forced into the canal before a suffi- 

 cient sectional area was obtained; and it was by dredging, at a 

 great expense and loss of time, that an imperfect navigable depth 

 of canal was subsequently had: and so clumsy were the operations 

 then carried on, that when all the locks were built and the gates 

 hung, one of the locks (the 20th) being at tlie commencement of 

 one of those bogs, and an aqueduct at its termination, it was dis- 

 covered, on the opening of the navigation, that a mistake of 4 ft. 

 6 in. had been made in the bog level, which was remedied by build- 

 ing an intermediate lock of the required fall. 



The Ballinasloe canal is 15 miles in length, 12 miles of which 

 are through bog, averaging from 20 to 46 feet in depth, and 

 bounded on two sides by lai'ge rivers — the Shannon and the Suck. 



Kylemore bog having been the wettest, softest, and the most 

 difficult to execute, we shall describe our mode of proceeding in 

 that locality. The length of this bog in the line of the canal is 

 3,100 yards, terminating at either end in ravines between it and 

 the adjacent bogs, leading from the upland to the river Suck, 

 which lies some distance north of the line of canal. The drain- 

 age of this lot was carried through those ravines with considerable 

 difficulty and expense, there being no intermediate lateral tap. 



Operations were commenced by making a drain in the centre line 

 of the canal throughout its entire length, 5 feet wide at top, and 

 1 foot wide at bottom, and 3 feet deep where jiracticable, (Plate 

 XIII., figs. 7 and 8, H.) In situations — and they were numerous 

 — where the fluidity of the bog would nut admit this depth, it was 

 sunk about 2 feet; and in some places not more than from 1 foot 

 to 18 inches. At 30 feet from the centre, on each side, drains of 

 like dimensions were made, which lined out the limits of the top 

 opening of the canal A A, allowing 9 inches to the foot slope, as- 

 suming that the subsidence of the bog surface would increase the 

 slopes to 18 inches to the foot, and give the required breadth at 

 bottom and top of canal when complete. At 4 perches, and at 

 10 perches from the centre on each side, drains B B, C C, parallel 

 to the foregoing, were made, of like dimensions, making seven in 

 all, including the centre drain; these were crossed at right angles 

 from the 10-perch drain north of the centre line, to the 10-percli 

 drain south of it, D D. At 10 perches distance from each other, 

 and in the intervals of these crossings, other crossings E, were 

 made from the 4-perch drain north, to the 4-perch drain soutli, re- 

 ducing the intervals longitudinallj' within these latter crossings to 

 5 perches. All of those drains were worked by slight sinkings, 

 keeping the top openings, as at first, to 5 feet, until the bog ac- 

 quired sufficient consistence to allow deeper incisions into it. The 

 centre drain and the verge drains were most worked, and the 



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