Page 10 - Minutes of Proceedings of Civil Engineers Vol CXCV 1913-14 Part 1

50 wENTwoRTIT-sHErLDs oN TrrE coNsrRucrroN oF [Minutes of below this level the excavation was continued down with 4-inch timber runners. Although a good deal of water flowed into the trench from the gravel bed, no serious difficulty was experienced on the west wall in carrying down the excavation, as the strata consisted for the most part, of sandy clay, which proved fairly impervious, The corresponding trenches on the east wall gnve mole trouble, as the strata below the gravel consisted chiefly of the fine sand, which ran freely into the trench through any opening in the timber, carried in by the water from the gravel bed above. By sinking a sump in advance of the excavation to dry the ground, and by keeping tho lunners always driven down as low ns possible, the foundation-level was reached in all c.'l,ses but one-although not without some risk. The danger which constantly threatened was th:r,t tho water or sand might enter in such quantities as to over- power the pumps, or to cause large holes behind the timbers, so. loosening the struts. One or two such holes discovered in process of sinking were stopped at once by cutting out one or two runners and filling the hole with gravel or other good material. Those who have had charge of this class of work will realize that it involves great courage and skill on the part of the timbermen to battle successfully with such conclitions. Dfficulties at the South EniI of Berth No. 48.-Only in one of these deep trenches was it found impossible to carry the excavation dorvn to foundation-level. This was at the last 100 feet length of the east wall, berth No. 43. Ifere the trench was surrounded with sheet- piling at back and front and at its south end. At its north end it abutted on the new concrete quay-wall, which had already been built to its full height. The sheet-piling along the back and front of the trench was returned, so as to close tight against this concrete rvall, Tho excavation of the tr.ench was carried down without great difficulty to about dock-bottom level, or to within 13 feet of foundation-level. Meanwhile, the work of constructing the northern portion of the dock having been a,lmost completed, a gap was cut in the enclosing bank and the water was allowed to enter. Although the dock was thus flooded, it was hoped that no water would enter the trench, as it was thought that the sheet-piling surrounding it, backed by a bank of earth which had been left untouched, would suffice to keep it out. At first it did so successfully, but after the dock had been floorled for about 3 weeks, and when the excavation t'blo*'s had been crlrlio