58 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



of 12 feet above the old dock sill level, the cast-iron washers 

 began to sink into the wales and break. To remedy this, pieces 

 of American elm 3 feet long by 12 inches wide by 6 inches 

 thick were placed under the washers. Then the wales ex- 

 hibited signs of giving way where the tie-rods passed through ; 

 as a precaution, additional wales were put on between each 

 of those originally in place with an extra tie-rod driven through 

 each additional wale at the intermediate distances, with a vertical 

 piece of elm overlapping two wales, so as to distribute the 

 bearing surface. The tie-rods were screwed up over these 

 vertical chocks. This treatment proved effectual in keeping 

 the puddle in place. 



When the puddling of the dam was near completion, the 

 structure showed symptoms of going out towards the river, 

 particularly near the crown of the segment. To prevent this, 

 an extra row of piles was driven for a distance of 200 feet run 

 at 30 feet outside the dam, 8 feet apart from centre to centre, 

 upon which a waling 14 inches square was bolted as low down 

 as the lowest tide would permit. From this waling, raking 

 struts 14 inches square were placed, reaching to the under side 

 of the waling on the dam at the level of 8 feet above the old 

 dock sill. It was considered expedient, during the time the 

 dam was in place, not to remove a quantity of contiguous soil 

 intended to be excavated, so as to prevent a " blow." 



All the other portions of the work within the low-water 

 basin being completed, the excavation was proceeded with, the 

 object being to lessen as much as possible the subsequent 

 dredging. 



When the excavation was nearly completed, the water com- 

 menced bubbling up in half a dozen places at about 30 feet 

 behind the dam. Additional struts were therefore placed on 

 the basin side as the structure commenced to warp a little, 

 and the puddle to settle down slightly. The bubbling up of 

 the water however continued, and after a day or two the nuts 

 of the tie-rods began to fly off, and it became evident that 

 the dam would not much longer resist the undermining and 

 the pressure from without; ultimately the dam suddenly 

 gave way. 



The head of water of 33 feet, rushing in to fill the empty 

 space of 14 acres, scoured a channel 30 feet in depth and 50 feet 

 in width within the basin. A large portion of the piles were 



