WATER IN FOUNDATIONS. 81 



to place the masonry on concrete resting on the bottom clay. 

 This would have given an average thickness of 14 feet of 

 concrete below the masonry. 



In accordance with this plan, after the silt had been 

 removed from the greater part of the site of the dock, a cutting 

 was made throughout its entire length on the level of the 

 upper surface of the bottom clay, which was found to dip 

 gradually from west to east. 



The bed of sand proved much thinner than had been 

 anticipated, varying from 2 to 3 feet, but passing in many 

 places into pot-holes in the clay. At the east end of the lock, 

 where it was expected that the sand bed would be of greater 

 thickness, the pot-holes were more numerous ; but in no case 

 was the sand bed continuously of the thickness indicated by the 

 borings. 



When the excavations had so far advanced that a part 

 of the surface of the bottom clay had been laid bare at the 

 east end of the lock, further progress was prevented by the 

 appearance of two springs or "boils " near the line of the sheet- 

 piling which had been driven from the return wall about half- 

 way across the lock entrance. The water from these boils, 

 which was brackish and charged with yellow sand, soon 

 mastered the hand-pumps which were fixed to clear the 

 foundation of water, and necessitated the abandonment of 

 the east end of the lock. A stank was made across the gullet 

 on the site of the east sill to confine the water to that end 

 of the lock. This stank was barely finished before an accident 

 to the river bank at another part of the works, gave the waters 

 of the Humber free access to the lock pit, and delayed the works 

 for three months. 



Soon after the boils started, and prior to the breach in the 

 river bank, a crack appeared in the shore piece of the north 

 basin wall, against which the coffer-dam abutted on the north 

 side of the lock entrance. Fear was entertained lest the water 

 from the basin should have found a passage beneath this wall, 

 the foundation of which nearest the basin was built on bearing- 

 piles, and the remainder, near the lock, on concrete resting on 

 the lower bed of clay. That this might be the case appeared 

 likely from the fact that the crack divided the wall vertically 

 near the point where the change in the plan of the foundation 

 occurred. It was thought possible at one time that the crack 



G 



