WATER IN FOUNDATIONS. 95 



The total collapse of the trench was threatened. Strong 

 lacings were inserted, while the centre piles and struttings 

 were partially suspended by long beams thrown across the 

 trench. 



The pumping was then reduced to the amount necessary 

 to get in. a piled foundation for the side walls at the highest 

 possible level. The holes were rilled in with chalk, and the 

 whole area of the trench was also covered with it, in order 

 to intercept as much as possible the silt brought up by the water. 

 Bearing-piles were then driven between the network of 

 temporary timbering, connected at the top by whole-timber 

 caps, on which a double thickness of elm planking was laid, 

 forming the foundation of the inner gate recess wall and the 

 heel-post stone. The timber platform was placed as high as the 

 level of the under side of the heel-post stone to reduce the 

 pumping to a minimum, and thereby obviate further ill effects 

 of the boil. 



Borings made east and west of the lock showed that the bed 

 of clay was over 15 feet thick, whilst at the blow it was only 

 2 feet thick. 



The excavations for the foundation of the outer and middle 

 gate platforms was taken in bands about 20 feet wide, the 

 alternate trenches being timbered, and after the masonry had 

 been built to a sufficient height, the intermediate bands were 

 excavated without timbering. 



The principal difficulty being anticipated at the inner gate 

 platform, it was proposed to excavate the foundations in small 

 areas enclosed by half-timber, grooved-and-tongued sheeting, but 

 after driving a short length of sheet-piling, about 25J feet long, 

 transversely, and two or three gauge-piles in a longitudinal 

 direction, some blows occurred at the surface, which was a little 

 above dock bottom, and considerable quantities of water came 

 up. In a short time several large holes were formed, and some 

 of the sheeting sank down and disappeared. Cast-iron pipes 

 were driven as deep as possible into the two principal springs, 

 and in one of these the water subsequently rose 14 feet above 

 dock bottom, and remained at this level, indicating the upward 

 pressure at this point. Clay puddle was tipped into the large 

 holes and well trodden in, one hole alone absorbing several 

 hundred cubic yards of puddle. The extensive area of the 

 disturbance was manifested by the cracking and settling of the 



