SOL- no 



1855.] 



LIGHTHOUSE ON THE NEW SOUTH SHOAL, NANTUCKET, U. S. 



121 



Cljc ^HuaHiiu |0unuiL 



TORONTO, JANUARY, 1855. 



Li3:lithou:e oa the New South Shoil, Nantuoket, U. S. 

 THE SCREW PILE— THE I'XEU.MATIC PILE. 



No work of a solid character placed on a submerged sand 

 at so exposed a point a-s New South Shoal, were it possible to 

 found one, could long withstand the power of the ocean. That 

 it would not be overthrown by the direct blow of the waves, 

 the successful resistance of the works just named (Edd3'stone, 

 Bell Rock, Skerryvore Lighthouses), at points where the incli- 

 nation of the bottom and the depth of water are calculated to 

 give greater force to the waves, prove beyond all reasonable 

 doubt ; but that its destruction would nevertheless be inevitable, 

 from the rapid and ceaseless process of the wasting of the 

 sands of the shoal, caused by the recoil of the sea, from the 

 mass, is no less certain. To provide a base of sufficient size 

 and strength to sustain the necessary superstructure, that shall 

 at the same time offer no very sensible obstruction to the free 

 passage of the currents and the waves, is the great desideratum 

 in founding works on submerged soils exposed to the batter of 

 the ocean. This desideratum the last few years has supplied in 

 the screw-pile of Mr. Alexander Mitchell, of BelfiLst, and in the 

 pneumatic pile of the late Dr. LawrenceHolker Potts, of London. 

 The next inquiry in order is, whether either of these modes is 

 applicable to the site of New South Shoal. After much reflec- 

 tion, aided in no small degree b}' the experience acquired in the 

 erection of the light-house on the Brandywine, I am of opinion 

 that the first, being the method of screw-piles, cannot be em- 

 ployed to found a work at that point : and for these reasons : 



1. That the screws could not be made to penetrate the 

 shoal to the required depth, by any means applied from a 

 floating body, moored in the tide and sea-way at the point in 

 question. 



2. That it is not possible to erect a temporary jixed struc- 

 ture during the working season at so exposed a point, at least 

 in time to be available for driving the screw-piles ; and, 



3. That if it were possible to raise such a structure in time, 

 it is doubted whether any power applied from it could insert 

 the piles to a necessary depth, into a sand so hard and compact. 



The screw-pile has been successfully applied in forming 

 foundations of light-houses on the JIaplin Sands, mouth of the 

 Thames; on the North Wharf Sands, mouth of the W3Te ; on 

 the shoal ground of Uolywood, Belfast bay ; and, in this 

 country, on Brandywine .shoal, mouth of Delaware bay. The 

 attempt to erect a light house on the north end of the Kish 

 Bank, in St. George's channel, by means of these piles, failed, 

 from no defect in the principle claimed for these useful appli- 

 ances in forming submarine foundations, but principally, as it 

 is understood, from the coming up of a heavy gale from the 

 south-east before the piles were properly braced and the dia- 

 gonal stays attached. The design to raise a beacon of scrcw- 

 pilcs on the eastern end of the Tongue Bank also proved 

 ."bortivc ; but, as the case of the structure on the Kish Bank, 

 from no inherent defect in the piles themselves. This beacon 



* Ab.strnct of a report to tho Senate of the U. S. commxinicntiTip, 

 in complinnce with a resolution of the Senate, ft Report &c. from Major 

 hartmiin Baohe, in rcfercnco to tho construction of a Lighthouse ij 

 Beacon on tho New South Shoal of Nantucket. 



Vot. lU., No. 0, Ja^tjart, 1865. 



was composed of five six-inch piles, and raised in position by 

 tho Trinity House. Sh jrtly after it was put up, it was dis- 

 covered that an accident had happened to it, and, on examina- 

 tion, it was ascertained that three of the piles were broken off 

 short, and the other two bent. The stump of the broken piles, 

 and the lower parts of the bent piles, were fuund peifectly up- 

 right, and the sand around them undisturbed ; showing the 

 structure failed from no fault of the lo'd they had taken 

 of the ground. Their condition indeed afibrds the best evi- 

 dence of the capacity of the screw pile on this point, as it 

 appears the force that was sufficient to break oflF three and bend 

 two wrought-iron piles of the size stated, was, at the same time 

 unequal to the task either of uprooting them or even chang- 

 ing their position in the bottom. As the force of the waves, 

 acting on such small surfaces as these piles presented, was en- 

 tirely inadequate to produce the effects described, the 

 destruction of the beacon was sought for in other causes. The 

 conclusion arrived at, at the time, and no doubt the correct one, 

 was, that a vessel had passed over it ; a conclusion in a measure 

 confirmed by finding the copper of a vessel attached to the 

 top of one of the bent piles. It may be remarked here, inci- 

 dentally, that accidents from this cause form the only real 

 objection, save the destructible character of the material, 

 either to the screw-pile or the pneumatic-pile, and only then of 

 works founded iu navigable depths. • 



The pneumatic-pile of Dr. Potts is of more recent origin 

 than the screw-pile, or, at least has not been so long known to 

 the public. It has not yet, it is believed, been successfully 

 applied in founding works, such as light-houses, beacons, har- 

 bouvs, (ic, exposed to the sweep of the ocean. That it is 

 practically applicable for the purpose there is every reason to 

 believe. The favourable opinion of those well known in engi- 

 neering and construction in Great Britain, communicated in 

 the report on the ice-harbours of the Delaware, dated the 28th 

 December last, may be received as conclusive, particularly as 

 it is supported by cases of application alieady made in other, 

 and in some respects kindred works, on this point. To this 

 testimony and to these cases the bureau is again referred for all 

 the information in possession of this office upon the subject. Of 

 the latter it is deemed sufficient for the present occasion to 

 recount merely the following instances in which these piles 

 have been used, to show that their size, both length and 

 diameter considered, would seem only limited in their applica- 

 tion to the power under the circumstances to Jiandle them. 

 Besides being employed, among other instances, iu the found- 

 ing of the piere of a viaduct in Anglese}' over an arm of the 

 sea, the bed of which is of running sand and gravel of great 

 depth ; in an experiment on Grain Spit to test the powers of 

 the piles to sustain great weights ; in the sinking of a pile of 

 large dimensions in a quicksand in Cornwall ; in the construc- 

 tion of a bridge over the Thames at Datchet ; and in the 

 foundation of part of a large viaduct on the Holyhead line of 

 railwaj-, a pile of this description, 3 feet in diameter, has been 

 sunk in the Goodwin Sands to the depth of 77 feet, to the chalk 

 formation ; and others of the enormous size of 10 feet diameter 

 as cofferdams, in the construction of the Midland Great 

 Western Railway bridge over the Shannon. To this list may 

 be added tho new bridge over the Thames from Putney to 

 Fulham, in which the piers will bo formed of faur c:ist-iron 

 cylinders 8 feet in diameter, carried to such a depth as not to 

 interfere with the dredging of the river. It is proper to 

 remark here, that other applications of both the scrcw-pjle and 

 pneumatic-pile either in constructions or in experiments, may 

 havo boot} made and noticed in tho publications of tho day, .pat. 



