1840.J 



THE CIVIL ENGINEER AND ARCHITECTS JOURNAL. 



265 



but the deposit of eartli had scarcely begun when an extraordinary 

 motion was communicated to the adjoining soil. In two places it was 

 lifted up b or 10 yards above the surface, the road w'as blocked up, 

 and several houses on the disturbed site were upset. It was found 

 that this operation proceeded from a stratum of clay, mixed with sand, 

 and soaked with last year's rains, so as to become fluid ; that the 

 weight of the embankment 30 yards high, and that of the superincum- 

 bent strata had put this pulpy mass in motion, and that it had disturbed 

 the adjoining soil on the slope of the valley, and had in several places 

 lifted up and broken through the upper strata. The cause was ap- 

 parent that water did the mischief, and though it might not have 

 shown itself immediately if the season had been dry, yet ultimately it 

 would have been productive of serious evil. To remedy this, there 

 were no other means than to stop the flow of water arriving from the 

 upper levels ; to carry which into effect it was necessary to cut the 

 clay stratum and replace by stone work, which would surround the site 

 on which the embankment was to be formed and divert the water. 

 This operation was found exceedingly difficult, having to be carried 

 on at a depth of from to 20 yards in a moving soil, saturated with 

 water ; it was long, very dangerous, and an accident might have wasted 

 much valuable time, the woi-ks of the embankment being suspended in 

 the meanwhile, and the stone-work itself being liable to be swallowed 

 up in a few years, and the work to be done over again. 



Under these circumstances the engineers thought it advisable to 

 have recourse to boring for the purpose of absorbing the water, and 

 applied to the General Well-boring Company at Paris. This mode 

 was also difficult, as the boring tube got plugged up in the soft stratum 

 as fast as it was emptied, but by means of good tools this was at last 

 got over. The first boring reached 20 yards and got into the upper 

 part of the chalk, notoriously full of fissures, and where the water was 

 rapidly absorbed. The second and third borings were carried to 35 

 and 40 yards in order to get at the chalky fissures which communicate 

 ■with the Seine, and feed the neighbouring wells. A series of borings 

 will therefore be carried round the emijaukment at proper distances 

 and drains if necessary made to carry the water into the borings which 

 can easily be kept clear by means of a valve and cord. It is proposed 

 also to apply this method to get rid of the water in sand, but this ne- 

 cessarily de|)ends on the strata, for we believe that in the Kilsby tun- 

 nel it would not have been practicable. 



SPEED ON RAILWAYS. 



Diagram, showing the variations in the speed of a locomotive engine 

 and train over a journey of 2i miles, on a level railway. In the 

 first instance starting from a state of rest and getting up the speed ; 

 then travelling one mile at the rate of thirty miles an hour ; and 

 ultimately being brought again (by the use of the break) to a state 

 of rest. 



From numerous observations, by R. Sheppard. 



Scale of Miles. 



S 



HYDRAULIC WORKS AT ALGIERS. 

 By M. Poirel, Engineer of Bridges and Roads. 



Trnnslatedfrom the Annalei des Pouts et Chaussei's by IV. H. Emory, 

 Jan., U. S. Topi. Ei!gr$.,fur the Franklin Journal. 



The port of Algiers was established as far back as the year 1530, 

 by Cheredin, brother of Barbarossa. Having made himself master of 

 a little island, in front of the city, which Spaniards had fortified, he 

 resolved, in order to secure it, and at the same time to make, at Algiers, 

 a harbour that would afford protection from the winds and from the 

 swell of the sea, to unite it to the town by means of a jetty. This is 

 called the Cheredin jetty, and is two hundred and twenty-three yards 

 long, and one hundred and twentj'-seven yards wide. Its direction is 

 nearly east north-east, or west south-west. 



Besides the Cheredin jetty, another has been built on the prolonga- 

 tion of the island, which protects the harbour from easterly winds, and 

 is called the mole. It is one hundred and seventy-four yards long, and 

 forty-five yards in its greatest width. This mole runs north-east and 

 south-west. These two jetties with the little mole on which the 

 Lazaretto stands form the boundary of the basin. It contains forty 

 thousand seven hundred and twenty-two superficial yards, and can float 

 sixty vessels, of which about thirty, may be vessels of three hundred 

 tons, and some few, eight hundred tons. Vessels of a larger class 

 anchor outside the basin. The greatest depth of water is sixteen and 

 a half feet ; but this may be increased by dredging. The Cheredia 

 jetty and tlie mole were foimd in a state of complete dilapidation when 

 Algiers fell into the hands of the French. These two works constructed 

 of loose stone, (rubble) were levelled to their base. The Deys were 

 in the habit everv year of having the stones replaced which were 

 carried away in the winter by the sea. 



Laugier de Tassv, one of the most faithful historians of the Algerine 

 regency, who resided there in 1727, says : — 



"The great mole (the Cheredin jetty,) being entirely exposed to 

 the north, to prevent it from being carried away by the fiu-ious swells 

 of the sea, which roll up the sand bank, stretching along this mole and. 

 out into the sea, they were obliged to keep the slaves of the beylick 

 employed the whole year carrying hard stones from a place near point 

 Pescade, to put them along the mole. The sea soon carried away the 

 stones thus deposited, but care was always taken that they should be 

 replaced." 



Large magazines of military supplies are placed on the Cheredin' 

 jetty, and it naturally claimed the first attention of government. 



The preservation of these magazines required that the loose stone 

 upon which they rested, at the base of the jetty, should be secured. 



This undertaking was confided to M. Noel, the engineer, in charge 

 of the hydraulic works at Toulon, from which he was temporarily re- 

 lieved. 



He rebuilt the entire body of the jetty to a height of sixteen and % 

 half feet above the water, with a thickness of six and a half feet. The 

 new masonry is of the very best kind, and possesses great solidity ; 

 unfortunately the insufficiency of funds placed at the disposal of the 

 engineer, and his limited time did not permit him to turn his attentiorr 

 to the foundation of the jetty which will soon require considerable re. 

 pair. 



The extremity of the mole, called the chop, in which the sea made 

 a large breach, was repaired in ISBl, but the new masonry being built 

 upon the fragments which the action of the sea had brought down, was 

 entirely destroyed by the first storm in the winter of 1832. All the 

 repairs made to the top of the work were necessarily liable to tire 

 same catastroplie, as the base upon which they rested was insecure. 

 It became necessary, therefore, before proceeding farther, to recon- 

 struct the base permanently and durably. 



The locality did not permit the engineer's resorting to the ordinary- 

 means of establishing a foundation by throwing over loose stones, (rub- 

 ble.) The shore to the west, where the quarries are, has not a single 

 creek or harbour where a vessel could load ; it is open to the ocean 

 and skirted by a reef of rocks which make the landing dangerous even 

 in a calm. The transportation of blocks of stone could only be effected 

 by carriages, a tedious and difficult operation with masses, which , to 

 resist the action of the waves, should measure at least four cubic yards. 

 Besides which it would have been necessary to carry these blocks 

 through the most frequented and populous part of the city, very much 

 to the inconvenience of the inhabitants passing to and fro. Another 

 difficulty presented itself, even if the obstacles to an easy transporta- 

 tion had been overcome. To give sufficient stability to the work at 

 the end of the mole, a long slope of at least one in ten was necessary, 

 which would have entirely obstructed the navigation, as the entrance 

 to the basin was already very narrow, being only one hundred and 



