392 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



ground settles or expands, and thus grips the pile to such an 

 extent as to materially increase the frictional resistance. 



The ground into which these piles were driven consisted of 

 clay and the argillaceous sandy beds below the London clay. 



The interval between the first and second observations was 

 about fourteen hours. 



Displacement of Ground by Piling. 1 However compressible 

 the ground may be, it will, on commencing driving particularly, 

 naturally give in the direction of the least resistance, which will 

 of course be towards the surface. 



It has been noted that, in ground consisting of the compact 

 sandy beds immediately below the London clay, the mean rise 

 of the surface over an area of 1248 square feet, into which 

 66 round piles had been driven 12 feet deep, was 0*75 foot. 

 The heads of these piles above the normal level averaged 1*33 

 square feet, therefore the total quantity to be removed to again 

 reach the normal level was 870 cubic feet ; from this a deduc- 

 tion of about one-fourth must be made to allow for increase of 

 bulk due to disintegration, leaving 650 cubic feet as the nett 

 quantity of solid material displaced. 



The quantity of timber actually driven was 676'36 cubic feet, 

 therefore the displacement of the ground due to the piles was 

 96 per cent, of the whole quantity of timber driven. 



In ground of a more argillaceous character, but still within 

 the sandy beds lying between the London clay and the lower 

 beds of blue clay, the rise of the surface averaged 0*875 of a 

 foot. This, over an area of 1520 square feet containing 80 

 12J-inch square piles, driven 19 feet into the ground, is equal 

 to 1330 cubic feet; deducting, in this case, one-fifth for increase 

 of bulk due to the disintegration, the quantity actually dis- 

 placed was 1064 cubic feet. The cubic quantity of timber 

 driven as piles was 1649 '30 cubic feet; therefore, the displace- 

 ment of the ground was 64 per cent, of the total quantity of 

 timber driven. 



In stiff clay beds, the upper part of which had been oxidized, 

 rendering the material more plastic and compressible, the average 

 rise was 1*20 feet, over an area of 1596 superficial feet, into which 

 105 piles, 12| inches square, had been driven 25 feet deep. 



The quantity of ground displaced, after allowing for increase 

 of bulk due to disintegration, was 1418*48 cubic feet. The 



1 U.P.LC.R,\oL Ixiv.p. ICG. 



