248 KENNIE'S AVAR DOCKS. PART VI I. 



interruption until the year 1826, when the whole were 

 completed. 



Their execution was attended with many difficulties, 

 and necessarily required a great deal of Mr. Rennie's 

 care and attention. The foundations were a soft run- 

 ning sand, extending to an almost fathomless depth. 

 The strong currents flowing past the place rendered it 

 necessary to adopt an entirely new system of operations, 

 which were carried out to an extent never before 

 attempted in so exposed a situation. That form of sea- 

 wall was devised which should most effectually resist 

 the strong pressure of the current, and the heavy swell 

 beating upon its outer side, without yielding to the 

 lateral pressure or thrust of the water of the basins 

 and the earth by which it was backed. At the same 

 time, the weight necessary to ensure stability must not 

 be such as to sink vertically. Mr. Rennie adopted 

 the means to secure these objects which he had em- 

 ployed with such success at Grimsby Docks in 1797, 

 namely, to take the like quantity of materials as would 

 have been necessary for an ordinary wall, and dispose 

 of them in such a form, that the same weight should 

 be distributed over a greater surface, thus diminish- 

 ing the vertical pressure. In the foundations of the 

 walls he also adopted the method employed by him in 

 similar works, of driving the piles and cutting off 

 their heads at an angle inclining inwards, or towards 

 the land side, laying the courses of stone at the same 

 angle ; by which a greater resistance was offered to 

 the pressure of the earth, and the building was pre- 

 vented from being pushed outwards, as was more or 

 less the case in most of the walls built on the old con- 

 struction. The entrance gates to the great basin were 

 also planned and executed with great skill, Mr. Rennie 

 carrying into effect the same simple but correct prin- 

 ciples laid down by him in his report on the Northfleet 

 docks, making the direction of the entrance suitable to 



