TESTING STABILITY OF GROUND. 403 



at a very high initial pressure. No hard-and-fast rule can 

 however be laid down, therefore the quantity and pressure 

 must depend in a great measure upon the character of the 

 material to be dealt with. 



Testing Stability of Ground. The following course was 

 pursued in testing the stability of the ground prior to deter- 

 mining the dimensions of the foundations for the Paris exhibition 

 buildings. 



A perfectly level surface, in the form of a square 118 

 feet wide, was first prepared. On this area four rectangular 

 cast-iron blocks 1 foot 8 inches square were so disposed 

 as to form the corners of a square, the distance apart from 

 centre to centre being 11 feet 8 inches. The spaces between 

 the blocks were then bridged over by girders constructed of 

 T irons. 



The girders were then uniformly loaded and the weights 

 carefully noted. With a total weight of 7'31 tons per square 

 foot, including the weight of the corner blocks and girders, 

 indications of settlement became visible ; during the night the 

 settlement increased to between 10J to 11 inches with the same 

 load. The loading was then continued until some of the blocks 

 had sunk completely into the ground, leaving the girders sup- 

 ported on the surface. 



The conclusions arrived at were that the ground was 

 capable of sustaining a load of 5 '43 tons per square foot; that a 

 certain amount of settlement might be expected when the load 

 reached 7'31 tons per square foot, and that it was totally 

 incapable of bearing a load amounting to 814 tons per square 

 foot. 



Details of Experiment made to determine the Stability of 

 the Ground. 1 In order to test the stability of the ground prior 

 to abandoning the piles in the foundations of the locks and 

 deep dock at Portsmouth, the following experiment was made 

 on the site of No. 13 Dock, the nature of the ground in that 

 position being the same as that in which the foundations of the 

 locks and deep dock would be placed. 



The geological formation was the lower tertiary, the strata 



consisting of the beds of very compact argillaceous and retentive 



sand subordinate to the London clay. A hole was sunk to 



about the excavation level, and on a stone base a brick pier, 



1 M.P.I.C.E., vol. Ixiv. p. 151. 



