40 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNTAL. 



I Febbuaby, 



screw points, it may be stated that when trying experiments upon 

 the various forms, Messrs. Ransome and May screwed a casting 

 of the form of fig. 9 to a depth of 4. feet into the gravel of the 

 yard of their works, and after fixing into it a pole 38 feet in height, 

 a man climbed to the top, and caused it to vilirate as much as pos- 

 sible, without apparently affecting the stability of the foot. A 

 steelyard was then attached to it, and a 

 power of 4 tons was applied with direct ver- 

 tical tension ; but without being able to 

 draw it out of the ground, and the pole is 

 now standing as firmly as ever. Since then, 

 with a larger sized screw point (fig. 8), a 

 mast 82 feet in height, with a vane at the 

 top 5 feet in length, has been placed, and 

 although only inserted 5 feet into the 

 ground, it is perfectly steady, with three 

 very short gye-ropes. 



Fig. 11 shows the applicability to smaller 

 objects, and a tent-pin has been selected as 

 the most familiar example, as it requires to 

 be removed so frequently, and shows the use 

 that may be made of the screw, for the 

 standards of fencing, and for an infinite 

 number of agricultural and other purposes. f'8- H- 



Remarks after the reading of the above Paper. 

 Mr. Brooks said he had considerable experience in the use and merits 

 of the screw-moorings, and must accord them his entire approval. It 

 was more conclusive to give facts than opinions, and therefore, although 

 he had not come prepared to address the meeting, he would state suc- 

 cinctly what had been done in the Tyne. A heavy ground chain, com- 

 posed of links each 3 feet in length, of round iron 3J inches in diameter, was 

 stretched along the bed of the river in the deep water, and in the direc- 

 tion of the current, instead of according to the old system, placing it as a 

 bridle across the stream (as shown i n the wood-cut, fig. 2.) To this 

 chain, at given distances, marking the centre of each tier, and the mid- 

 distance between, were shackled studded link mooting-chains of 2j-inch 

 iron, which had been previously laid down, with the lower extremity of 

 each attached to a screw-mooring, inserted into the bottom of Ihe river at 

 each spot to depths varying from 10 feet to 20 feet. The chain attached 



Fig. 12. 



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to the sheer-screw was two fathoms longer than that to which the mooring, 

 screws were shackled, so as to allow the strain to come upon Ihe niooring- 

 screws, instead of upon the sheer screws, which latter were only intended 

 to bear the strain arising from the vessels ranging across the stream, when 

 the wind was off either shore. The moorings were placed where the 

 depth varied at low-water spring tides from 15 to 24 feet. The bed of the 

 river consisted of sand for about six feet in depth, and then clay for about 

 four feet; rock was generally met with, but the latter, where it consisted 

 of a stratum of shale, was penetrated by the wrought-iron screw point, 

 for about one foot, or as far as the underside of the table of the screw. 

 The screw-moorings which were used were four feet in diameter, and un- 

 less they were stopped by rock, they were easily inserted to a depth of 15 

 feet into the sand and clay, in about an hour and a half. Some of them 

 had been screwed down to a depth of 21 feet in less than two hours. It 

 must be observed, however, that a very efiicient apparatus was constructed 

 expressly for the operation (figs. 12, 13, and 11) ): it consisted of a hop- 

 per barge, with semicircular leaves on each side, forming, when lowered, 

 a platform of about 40 feet in diameter. The capstan had eight bars, each 

 20 feet in length, requiring four or five men to each bar, according to the 

 quality of the soil into which the screws were to be forced ((ig.6.) Each 

 'jciew was intended by Messrs, Mitchell and Son to bear a strain of four 



heavy ships ; but during the crowded state of Ihe port, for several months 

 of ihe winter of 1847, double that number of vessels generally made fast 

 to them. 



Mr. Walker said, with respect to the screw.piles for foundations for 

 lighthouses upon sand or mudbanks, those upon the Maplin Sand had 

 been very successful; for, although the sand on the surface had shifted 

 considerably, being carried away and brought back again by different 

 states of the sea, the screw-piles stood perfectly ; in fact, tli*?y offered no 

 obstruction to the passage of the waves, and caused no scour. With 

 respect to the Goodwin Sands, it was not generally known, that the Cor- 

 poration of the Trinity House had caused a beacon to be placed on the 

 back of the sand, consisting of a base of cut stones well secured together, 

 with an octagon-sided vessel, or caisson, which was towed to the spot and 

 grounded; the sides were then unshipped, leaving the bottom under the 

 mass of stone, and an iron beacon mast was stepped into it. This beacon 

 was now the only one in existence upon the sands. He believed, that 

 beacons, or other structures, erected upon screw-piles, would stand as 

 well on the Goodwin Sands as on the Maplin and other places. Schemes 

 for lighthouses to be placed upon the Goodwin Sands were constantly 

 pressed upon his notice; but it did not appear to be understood, that any 

 solid edifice, to be erected in that locality, must have its foundation carried 

 Fig. 13. Fig. 14. 



down to the chalk, to insure its durability. The Corporation of Ihe 

 Trinity House wished it to be understood, that it was not their intention 

 to place lights upon the Goodwin Sands ; but rather to place them around 

 that spot, in order that vessels might avoid its dangers. At present, float- 

 ing lights were employed ; but if fixed lights could be placed in Ihe same, 

 or equally useful localities, he had no doubt the project would be enter- 

 tained. He had a good opinion of the screw-piles for this purpose, and 

 when the question came before him in a tangible form he should be ready 

 to give it his attention, for he thought, that a lighthouse could be erected 

 on that principle, in a difficult position, more economically than by any 

 other plan. Tlie Corporation of the Trinity House was now about lu test 

 the stienglh of iron lishthouses, by erecting one upon the Bishop Rock, 

 in Ihe .Scilly Islands, in a situation which was even more exposed than 

 Ihe Eddystone. The plan adopted for fixing the foundations was, to bore 

 holes in the rock, to clamp masses of ircm into them, and then holt down 

 the lighthouse upon these fixed irons. Wliether this system would answer, 

 or whether stone or iron for the structure would be Ihe most durable, re- 

 remained to be proved. At the Point of Ayr, Mr. Walker had adopted 

 another system for the foundation of a lighthouse placed upon piles. 

 Cast-iron cylinders were sunk into the bank, the piles were plated within 

 them, and each was tilled with concrete; tiiis system was practicable in 

 certain situations, where the bank was dry at low water, but was evidently 

 not so generally available as the screw pile, which offered great facilitie.s, 

 by the rapidity vvilli which it could be inserted even at considerable depths 

 under water, with very simple and inexpensive apparatus.* 



* Mr. Brunei has recently caused a very interesting and conclusive experiment to be 

 tried, near tile proposed site of the bridge for carrying the South Wales Kaihvav across 

 the river Wye, at Chepstow. A cast-iron cylinder, ."i feet diameter externally, \\ inch in 

 thickness, cast in lengths 10 feet each, with internal socket and jogi^le joints, secured 

 with pins and run with lead, was armed at the extreme bottom with a sharp wrought-irou 

 hoi>p, and a little above it was a helical flanch projecting 1*2 inches all round from the 

 body of the cylinder, around which it made an entire revolution, rtilh a pitch of 1 inches. 

 Ily means of capst^n-bais worked by manual labour, and by strong winches, this cylinder 

 was screwed into the ground, near the bank of the ri-er, but (ml of the influence of the 

 tide, to a depth of ."iH feet, in 4S hours and 14 minutes, through stitf clay and sand down 

 to the marl rock. In descending to that depth the cylinder made 142 levolutions. and 

 the average rate of sinking per revolution, very nearly accorded with the pitch of the 

 screw. The time quoted Is only that which was actually consumed in forcing the cylinder 

 down, as it was allowed to rest for long periods, whilst the interior core of clay was re- 

 peatedly cleared out, and on account of the breakai^es of the lopes and the capstan-bars, 

 and other casualties incidental to all first experimeuls. It is the intention o Mr. Brunei 

 to try a cylinder d feet diameter, with a larger helical flanch or screw, before deciding 

 upon the dimensions of the cylinders for the foundaiions ol his bridges, to be placed in 

 situations where there is a great depth of mud, stiff clay, and sand. Of this and the 

 subsequent experiments, accounts may probably be given hereafter. 



