94 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



by a sufficiently large quantity of concrete in bulk. As the 

 compartments were rilled with concrete, the boards were with- 

 drawn so as to allow the concrete to unite and thus avoid 

 vertical joints. 



Alexandra Dock, Hull. 1 In the foundations for the lock at 

 the Alexandra Dock, boils which occurred in the bottom 

 of the trenches were dealt with by the engineers in the 

 following manner. In the western trench, the clay was found 

 at 51 feet below high-water springs, or 2 feet G inches 

 lower than was anticipated. At one point in this trench a 

 boil occurred which was dealt with by placing an iron 

 pipe in the hole and surrounding it with chalk rubble to 

 the surface level of the clay. This was then covered with 

 Portland cement in bags, and upon this the foundation con- 

 crete was laid. The water at first brought up a great deal of 

 sand and fine silt ; but eventually, when the concrete had set, 

 it flowed away quite clean and clear through the pipe, and, as 

 the masonry was built up, it was led away by a horizontal 

 pipe to a sump. 



The first length of the foundation at the north end of the 

 west trench was excavated in remarkably dry material; the 

 clay being reached at a somewhat low level, and running 

 irregularly across the trench. The bottom suddenly began 

 to heave, and soon the water burst up in two or three places 

 and rapidly filled up the trench, mastering the pumps. Though 

 additional pumping power was provided, the impossibility of 

 pumping out the water to the required level was apparent, 

 not only on account of the great volume of water to be dealt 

 with, but because of the large amount of extremely fine silt 

 brought up with it from below the bed of clay, which was thus 

 gradually undermined, so that the sides of the timbered trench 

 settled very much, and large holes appeared in the adjacent 

 ground, forming fresh exits for the water from below, whilst 

 the material was brought up into the trench through the main 

 blow-hole. These holes were stanched by tipping in clay 

 puddle mixed with stable litter, straw, and bags loosely filled 

 with Portland-cement concrete. 



Soundings showed that the bottom of the trench was 

 covered with a layer of silt 5 feet 9 inches thick; while ;i 

 rod could be put more than 40 feet down the blow-hole. 

 1 M.r.l.C.K., vol xcii. p. 150. 



