[58 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



at each point, reaching from the upper surface of the blocks 

 to the rock. 



These posts or keys projected 12 inches into each block of 

 le'ton, and were made up of two logs of timber 12 inches square, 

 jointed and bolted together. To make up the dimension of 18 

 inches, one side was smoothed off, and close planking G inches 

 thick well secured with bolts and treenails ; the joints between 

 the timbers and the planking were then well caulked. 



The largest opening that occurred at any vertical joint was 

 5 J inches after all appearance ceased. The keys were in all cases 

 found to answer their intended purpose perfectly. 



The joints on the inner face were, when the basin was 

 pumped out, carefully cleaned out and walled up with masonry 

 to a depth of 1 foot from the face. On the outer face a pad 

 secured to a piece of timber was firmly braced against the wall, 

 until sufficiently tight to prevent the escape of fine mortar or 

 hydraulic cement which was injected through a tube under a 

 head of about 10 feet above the wall. 



TIMBER WHARFING Alexandra Dock Entrance, Hull. The 

 timber wharfing (Fig. 139) forming the sides of the trumpet- 

 shaped entrance to the lock is constructed in bays of 10 feet 



span generally, and 3 feet only at 

 the corners. The front and back 

 piles are 61 feet long, 14 inches 

 square, braced longitudinally and 

 transversely with timbers 13 

 inches square and 14 inches by 

 7 inches, and covered with a 

 5-inch decking. Grooved and 

 tongued half-timber sheet-piles 

 were driven all along the front. 

 This sheeting was driven simul- 

 taneously, all the piles in one bay 

 being pitched together and dri \m 

 about 6 feet at a time, until tho 

 whole bay was driven down. Tins 

 method of driving ensured the 

 tongues being properly engaged 

 in the grooves, and the sheeting being very close and ti^ht. These 

 piles held up the material at the back while the river bed was 

 deepened in front. During construction, the mud accumulated 



L.W.O.S.T. 



SCALE 



FIG. 139. 



