• Abstract and Figures
• Public Full-text

42 WILLIAXS ON THE NANCRESTER SHIP-CANAL. [Minutes of (Paper No. 21170.) ‘‘ The Manchester Ship-Canal : Mersey Estuary Embankments and other Works.-Runcorn Division.” By Sir EDWARDLEADER WILLIANS, M. Inst. C.E. THEestuary portion of the Xanchester Ship-Canal extends from its commencement at Eastham toRuncorn, a distance of 122 miles. Jn this length the canal passes along the southern bank of the River Mersey, about one-half being inland, while the otherportion is on the side of the foreshore, or crosses embayments ; embankments were therefore required to maintain the water in the canal at its proper level at low water. The preceding Paper deals with the embankments between Eastham and Ince, but the embankments between Ince and Runcorn were in the division of the canal of which the late Mr. Harold Abernethy, M. Inst. C.E., had charge ; and in order that the Proceedings of the Institution may contain a complete record of the mode of construction of the embankments, the Author proposes to describe the portion of the works superin- tended by Mr. Abernethy, whose early death has been a loss to the profession. The depth of water in the canal at the ordinary water-level is 26 feet, but as the lock gates and sluices at Eastham are opened when the tidereaches the ordinarywater-level in thecanal (whichis 14 feet 2 inches above the Old Dock Sill datum atLiverpool), spring tides give a depth of between 30 feet and 33 feet in thecanal from Eastham to Latchford, a length of 202 miles, At high water of all tides that rise above the ordinary level of the canal, which repre- sents a high neap tide, the lock gates and sluices at Eastham are closed, when the tidal water above ordinary canal-level is passed out into the Mersey through the large sluices at the River Weaver and at Randle’s Creek aboveBuncorn. Until the 7th February, 1897, the tide also flowed out of the canal through three tidal openings at Ellesmere Port, the RiverWeaver and Runcorn; these are now all closed. In designing the embankments, the Author had to consider the pressure against them at spring tides during the construction:of Downloaded by [ University of Sussex] on [12/09/16]. Copyright © ICE Publishing, all rights reserved. Proceedings.] TVILLIAMS ON THE UANCHESTER SHIP-CANAL. 43 the canal, as theembankments had to acttemporarily as dams after the water between the embankments and the shore had been pumped out to enable the excavation of the canal to be proceeded with. The embankments had to be formed on foundations of silt, sand, gravel, clay orsandstone rock, and therefore varying designs were necessary, particularly at Ellesmere Port and at Runcorn. At the latter place, where the estuary is narrow, the Nersey Conser- vancy required a concrete wall to be substituted for an embankment in order to diminish the abstractionof tidal area near the Runcorn Bridge, which has three spansof 300 feet each, one-half of the span on the Runcorn side being taken for the canal and concrete wall. The material for the embankments, obtained from the cuttingson the canal, consisted principally of boulder clay;after this had consolidated, the slopes were faced withheavy dressed-stone pitching. The action of the tides on the clay, combined with the weight of the locomotives and wagons which conveyed the spoil along the top of the embankments, consolidated then1 quickly in a very satisfactory manner ; when the waterwas pumped out from withinthe embankments,to enablethe excavation to becom- menced, they proved to be watertight even at the highest tides ; though, as had been anticipated, there was slight leakage under them in some places, where either gravel or sand formed the base. Wherever an embankment was afterwards opened, it was found that the clay was SO closely compacted as to resemble the original beds from which it had been taken. In the detailed account of each embankment, it will he seen that trouble arose at some places where the foundation was of porous strata, but this was overcome by using sheet piling, and the total amount of pumping during the excavation of the canal inside the embankments was less than had been anticipated. The difference between high spring-tide level and the bottom of the canal was about 30 feet, but the pressure from outside ceased after the exca- vation was completed and the canal had been filled with water. At low tide less pressure has since existed, due to the canal being then kept at the level of a high neap tide. Temporary cross-dams were adopted at various points to reduce the risk of damage in case of the tide breaking in before the canal was filled; no such case, however, occurred. These cross-dams wereuseful in filling the canal, which was done in compartments,first by large iron pipes or timber shoots, and, as the water rose higher, by cutting through the dams. River Gowy Siphons.- The raisedwater-level of thecanal required siphons to be carried under it and the embankments, to Downloaded by [ University of Sussex] on [12/09/16]. Copyright © ICE Publishing, all rights reserved. 44 WILLIAMS OX THE DIAX’CEIESTER SIIIP-CANAL. [Minutes of passland-drainage at places where low-lying lands werefor- merlydrained at or near low water, flap-doors keeping back thetide at high water. Thelargest of theseworks was con- structedto carry the River Gowy underthe canal at Stanlow Point. It consists of two siphons placed neartogether, each 12 feetin internal diameter; they are built of cast-iron seg- ments, the joint flanges being turned andrecessed ; they are inside the siphons, theintervening spaces being filled with cement so as to leave a smooth surface. Sixsegments were required to complete the circumference, andthey were so arranged as to break jointwith each other;the plateswere 1 inchthick, fastened by bolts lt inch in diameter. The siphons were laid in a heavily-timbered trench 50 feet below the level of the ground. Including the brickwork-chambers at each end, each siphon was 400 feet in length; they are 4 feet below the level of the bottom of the canal, resting on a bed of concrete 2 feet thick, which is founded on clay; 1 foot of concrete waslaid over theupper surface of the siphons. On the land side a pair of Stoney sluices are fixed to allow of either siphon being examined if necessary, and also to enable the whole ffow of the River Gowy to be concen- tratedthrough one siphonfor scouringout any deposit. The river has up to the present time kept the siphons clear without using the sluices. Ellesmere Port Embankment.-The method of driving the timber- piles throughthe sand-bank at Ellesmere Portis described in detail in the preceding Paper. The me of water under pressure was completely successful, and it is shown that timber-piling can be driventhrough sand even withgreater ease thanthrough ordinary soil. About 13,000 whole timber-piles were driven, the length of the sheeting-piles being 35 feet. At low waterthe embankment is free from leakage. The closing of the gap left in the Ellesmere Port embankment €or the passage of traffic was an interesting work. It wasfirst attemptedduring one period of low water. Many longtrains of wagonswere filled withclay and stoneready for tipping on each side of the gap, the quantity of material accumulated beingamply sufficient to close thegap if it could allhave been tipped before thetide reached high-water level. All went on well for some hours, when a locomotive got off the line and blocked the passage of the wagons, with the result that the tide broke through the dam before it was completed. It was then resolved to erect a high timber staging across the gap, and to tip the stone and clay from the staging in layers, allowing each tide Downloaded by [ University of Sussex] on [12/09/16]. Copyright © ICE Publishing, all rights reserved. Proceedings.] WILLI~MSox THE XANCHESTER SHIP-CANAL. 45 to flow over and consolidate it, the water being retained in the canal. This plan filled the canal gradually, and ina few tides the work was satisfactorily completed. The experience of the Author on the works of the Severn navi- gation,where it was necessary todivert the river into new channels and to raise the water-level untilit flowed over the weirs built in them, convinces him that a gradual lifting of the river- bed by materials that can resist the scour of the water over it, thusacting temporarily as aweir, is amuch safer planthan concentrating the whole scour of the river into a gap by tipping from each side. In one case on the Severn the force of the water when the river was thus narrowed carried away blocks of stone 10 tons in weight a distance of 100 feet. Weston Point Em.bankment.-The embankment from theRiver Weaver sluices to No Man’s Land, at Runcorn, is 14,100 feet long. Figs. 7, Plate 4, shows it commencing on gravel, afterwards passing through clay, but the greater portion is founded upon sandstone rock. This embankment was formed by tipping rubble-stone along the line of the foot of each side of the bank. From the tops of these stone footiags, grabs worked by steam-cranes removed the sand and mud down to the rock, when clay was tipped in to form the hearting of theembankment, which was protected duringthe period of consolidation by being faced on the estuary side with large blocks of stone roughly placed on the slope. After allow- ing time for the bank to consolidate, these blocks were dressed to form heavy coursed pitching for the faces of the embank- ment,the smaller stones being used on thecanal side of the bank.

Load more

  8

Copy Link