WATER IN FOUNDATIONS. 83 



As soon as the water was sufficiently lowered to admit of a 

 pile-engine being got to work, the row of sheet-piling across the 

 dock was continued to the back of the south wall of the lock ; a 

 row of sheet-piles was also driven along the back of this wall for 

 a distance of 110 feet. It was considered the more necessary at 

 this time to enclose the east end of the lock with sheet-piling, as 

 no fixed conclusion had been arrived at as to the immediate 

 source of the boils. This proved eventually to be far more deep- 

 seated than it was assumed to be at first, and in no way 

 connected with the superficial strata, through which the piling 

 hitherto driven had penetrated. 



After the water had been pumped out of the lock pit, the part 

 excavated for the foundations was found to be filled with mud to 

 the height of the sill level, or to 23 feet above the rails of the 

 lower waggon road. Much of this mud was raised to the level of 

 the top of the river bank by a large chain-pump. To assist in 

 removing this mud, a 6-inch syphon was laid over the coffer-dam, 

 and by the water from this source combining with it, a continuous 

 stream of liquid mud was kept flowing to the chain-pumps. 

 The drier material was removed by swing and horse roads, and 

 by waggon roads in the ordinary way. At the east end of the 

 lock there was laid bare a large bed of sand deposited by the 

 water flowing from the boils, which as yet gave no signs of 

 activity. 



The dam parallel to the railway creek having shown signs of 

 yielding, and as there was no means of strutting from the lock 

 aide, inasmuch as all the lower part of the excavation was still 

 filled with mud to a depth of from 10 to 15 feet, preparations 

 were made to drive a row of sheet-piles along the back of the 

 north wall of the lock, at a distance of 20 feet from the foot of 

 the dam, and also two rows across the lock at distances of 74 

 feet and 144 feet respectively, from the row already driven at the 

 entrance. 



Before much progress had been made with this piling, a boil 

 appeared not far from the centre line of the lock and near the 

 site of the east sill. A circular rim of sand about 5 feet in 

 diameter first rose above the surface of the mud and water, 

 in the centre of which a hole extended to a depth of 26 feet. A 

 pile 25 feet long, driven into the centre of this hole, disappeared 

 below the surface of the water after a few blows. 



Signs of failing in the dam became more evident ; several of 



