Page 5 - Minutes of Proceedings of Civil Engineers Vol CXCV 1913-14 Part 1

(( f 'r'rrceerlings,l THE wHITn STAR " bOCK AT SoUTHAMPToN. 45 rrr.rrtl, known locally as green sand " on account, of its colour. This '! ,irr.rrrl is less slippery than the clay, but it is equallyunsatisfactory as n, foundation, owing to the fact that it is highly charged with water, tt l,lrtr slightest movement of which oruses the sand to run." There is rrlways a, danger, therefore, that, after a length of wall has been lrrrilt on this sand the excavation for an adjoining length of wall rrny cause the sand and water to t'run " from under the first length, t,lrus undermining it, and perhaps reducing the bearing area of the sruntl to a dangerous extent. The new walls, however, had to be lruilt, on these strata, as trial borings showed that it was impossible l,o obtain a better foundation-such as gravel-by excavating to :ruy reasonable depth. PonrroN A (W-u,r,s Burr,t rN rno Dnv). Dedgn of WalL-The design of the quay-wall for berths Nos. 43 to 47, lying to the north of the enclosing bank, is shown in Fig. 3, Plate 2. It will be noticed that the toe of the wall is made long- projecting 13 feet from the cope-line-so as to reduce the pressure on the clay under it, and that it is reinforced with old rails on its unrler side. The base of the wall has a slope of 1 in 8 downwards from front to back, This slope is regarded as a very important uitl to the stability of the wall, although many engineers discard it, proferring to carry tho front of the wall down to the same level rr,s the back (see Appendir I, p. 66). The steps at the back of the rvtll are made wide, so that the weight of the earth backing shall lronr fully on them. The face of the wall is plumb from cope to low-water line, and is battered I in 10 below. The whole wall is brrilt of 8-to-1 gravel concrete, with a granito cope, and is provided with a trench on top to contain water- and electric-power mains. Sealing the Encloeing Banlt.-In constructing this portion of the rlock, which lay to the north of the old enclosing bank, the first opera- l,ion was to make that bank fit for excluding water. The bank was formed of chalk, which was mostly in lumps and very porous. Its t:ross section is shown in Fig. 4, Plate l, from which it will be seen t,hat it lay on a bed of peat, overlying the gravel. It was tightened lry driving half-timber sheet-piling along its toe and by grouting the joirrts of the stone pitching which covered. its seaward face. More- (,ver, a large quantity of mud and clay had been tipped out on to the irrside face of the bank at its west end, which helped to keep it wttertight. At the east end, lump chalk had been thrown out irrside the bank instead of the mud and clay, so that the ground here ryrw all veryporous. In order to remedythis, a line of grooved.and