Page 10 - Minutes of Proceedings of Civil Engineers Vol CXCV 1913-14 Part 3 Correspondence
P. 10
I'rrxreerlings.l THE " WI{ITE ST,\R " DO0K AT SOUTHA}IPToN. 725 tls l,o its qualityrand consequentlyas toits true vah:e:r,s il structurrl ilr.colson. lrlxdicnt. Tho conditions to be met and the object to be attained rvcre, of course, the chief factors deterurining a decision. Mr. II. P. ReMsay Coprr,ero observed that apparently no grcat trrr. Copctrncl. trrlilnce was placed upon the information delived frour trial bolings rts to the sub-strtrta, and presumably the Author nnd the contlu:tors lrreferrcd to rely upon exporience of similerr the vicinity or of other dock-works with which the names of the contractors were :r.ssocilted. Before commencing work in connection with the rkrcks, tttention was naturally directetl towards rendeling wrrter- t,iglrt tho enclosing bank, which h:r,d been built some time previously, rrrrd appiurcrtly with not too"much care, lrnving regard to the use to lvhich it rv;u intended to be put. It would be seen that in spite of the preventive mensures adopted, a million gallons of wnter, found its way into the workings and hrd to be pumped out daily. The cross section of the ground on which this bank wls built showed that the sull-strata were peat, gravel, and sand, and it rvas noL ditlicult to rrnderstand that the driving of sheet piling through these stra,ta musb disturbed whatever equilibrium rvns in them. Further, as it rvl,s practically impossible to drive piling accurately and without rleviation from the vertical, it was not sur.prising that these means rvele found ineffective. IIe doubted whether, if this bank hrrd been considered as a defective resorvoir errrbankment, many hydraulic cngineers woultl have advised similnr treatment. In the case of inrushes of water', dock-engineers relied upon sheet piling and powerful pumps; but there were several indications in the Paper that those means 'wero not, always reliable. For an outrush of rvirtcr a hydr:rulic engineer relied upon clay puddle, and Mr'. Oopela,nd suggested that if a trench had been dug about 4 feet :r,bove high-wr,ter level and carried down to the sand, which l,pparently contained a certain amount of clay, and, on a footing of 2 feet of gravel concrete, clay puddle hnd been brought up to the surface, the enclosing bank would have been rendered as water- tight as was humanly possible. He suggested that the excavation of 30 feet, of earth over the dock-area was the cause of nearly a.ll the difliculties met with in the trenches, owing to the fact that the equilibrium of the highly sensitive substratum was destroyod by removing this weight from the front, of the trench, and leaving it rr,t the back. This conclusion was borne out by the Author's description of the sinking of 100-foot trenches in the solid from the original ground-surface to a depth of 73 feet without difrculty, because the equilibrium of the underlying strata had not been 'listurbed. This argument was also substantiated by the erperience
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