Page 18 - Minutes of Proceedings of Civil Engineers Vol CXCV 1913-14 Part 1

58 wENTwoRTH-sIrEILDs oN THE coNsrRUcrIoN or' [Minutes ot iritervals around the piles, extending from dr.erlging-level up to low- wator level, The piles were driven first, nnd then the buttresses were formed by surrounding the site of each buttress with lO-inch creosoted timber sheet-piling. The pocket thus formed was grabbed dorvn to dredging-level, and filled with concrete deposited under water in boxes lvith bottom doors. At intervals along the jetty six smaller blocks or buttresses of concrete, 20 feet by 17 feet, rvere built from low water up to quay-level, resting on the l&rger buttresses below thern, and in these were embedded six large bollards, rvhich can be used for warping vessels in <.rr out of the dock. Pontrow C (Wlr,r, Burr.r tw run llrent or ruE Berx). (Berth No.41.) Deaign of Wall.-This wall differs from both the rvalls previously described, in that the portion below low water consists of concrete piers and arches, with curtain-walls between tbe arches. The design of the wall is illustrated in tr'igs. 11, Plate 2. It was decided to build it in dry trenches, to be sunk right through the bank and through the strata below it. These strata were known to consist for the most part of fine silty sand, with occasional seams of clay, and it was anticipated that the process of sinking the trench would be difficult-as indeed proved to be the case. Accordingly the pier-and-arch design was adopted, not so much with a view to economize material, as with the idea that each pier when built would run no risk of being undermined when sinking for the next pier. The baseof each pier was sloped from front to back, as in the other walls. The piers were made wide in proportion to their height, but the toe projected only 5 feet from the cope-line, and was not, reinforced. In order to retain the ground between the piers, concrete curtain-walls were built, and at about low-water Ievel the piers were connected by substantial concrete arches. Above the arches is a continuous face-wall of concrete, capped by n grl,nito coping, and provided with a trench for water- and power-mains. With this nrrangement the load on the bases of the piers is of course consirlernble, nnd is probably a good deal more than the ground undenretth thom could carry safely. At one time it was intended to increase the srrpporting-power of the ground by driving bearing- piles untler elch pier. This was found to be impracticable, however, antl in rnost owes the piles were omitted. Accordingly, some device had to be adopted to retluce the pressure betlveen the pier and the grountl on which it rested. 'I'his was effected by constructing the