Page 9 - Minutes of Proceedings of Civil Engineers Vol CXCV 1913-14 Part 1

I'r'il,nnrliilgs.l TIIE '(WHITE STAB" DOCK AT SOUTEAMPTON. 49 \l'lrtlo the trenches were fairly dry, all runners were drawn, the r loft by each runner being filled as much as possible with gravel ',rrl -When ',r r.$'oopings from the concrete. the wall had been built rrlr t,o thc top of the trench, it was continued upwards in much the ,'ilrr! woy, except that the concrete, instead of being lowered by , lrrls travelling on the trenches, was lifted by Scotch crarres I r',r vr,lling either in front of or behind the wall. As the wall rose it rlrrx lrrr,cked with clayand sand from the excavationof the dock-area. I t i.{lict tl ties i'n Tr ench- Ercauation.-The bulk of the trench-excava- liorr rvns carried out in the manner described, without interruption, I'rrl, rut one or two places difficulties wero encountered which rrrtlssitir,ted special treatment, and which may be shortly described I r,'t'rr. \\'lrcn the bottom of the trench was in clay there was a distinct l for it to rise before the concrete was deposited, and even ',nrlrrr(:y rvlrur thc first 2 or 3 foet had been laid; and vertical diagonal lirrrlxrrs had to be inserted at intervals to prevent the middle piles l'r',,rn lifting. 'When the trench-material was of a sandy nature, rr grxrrl deal of it was washed in at, the backof thetrench,and at one ,,r'l,wo places large subsidences took place, which showed as pot- lr'Lrs about l0 feet in diameter in the slopo above the trenches 'l'lrtrse pot-holes were filled as they occurred. ,\ serious difficulty occurred at the north end of the west wall, lx,r'th No. 46, where at one time a long length of trench threatened l, collapse. A length of 260 feet was being excavated, when il, rvts observed that the tops of the centre piles were gradually l,,rrrring over towards the south, carrying with them the struts which lr.st,txl against them. This movement was partially arrested by irrscrf,ing horizontal diagonal timbers, and a length of 130 feet of l,rrrrrch, where the greatest movement was observed, was pushed f,rrw:rrd to completion with all possible speed, the concrete wall lx,ing built in this length without removing the struts and walings. 'l'lris had the effect of arresting the movement, and no further rlilliculty was erperienced at this point. The occurrence emphasized I lrrr rrecessity of opening the trenches in short lengths, which were rrl'l,olwards limited to about 100 feet. At the south end of each wall, where it approached the en- lkrsing bank, the trenches were sunk from the ground-surface (rr,lruut quay-level), thus attaining a maximum depth of 73 feet. 'l'lrcse trenches \Fere canied out in lengths of 100 feet, which were rr rrnpletely surrounded by whole-timber grooved-and-tongued sheet- ;,ilirrg, driven down to the gravel, and about 35 feet in length. 'l'lro trench was sunk down to the gravel without difficulty, and [rur rnsr, c.E. YoL. cxcY.] E