30 The Drainage of Fens and Low Lands. 



fixing the depth to which the piles are driven, consideration must 

 be given to the probability of the deepening of the out-fall, either 

 by improvements or natural scour. After the sluice has been 

 built cement grout should be forced under the floor^ by pumping 

 it in through holes bored in the planking, and afterwards 

 plugged. By this means every cavity becomes filled up. 



The illustrations given are examples of a small sluice with 

 8 feet opening built on a silt foundation, and of a larger 

 sluice with three openings of 14 feet each, suitable for the 

 draining of a district of about 20,000 acres.* 



In situations where a solid foundation can be obtained 

 the difficulties of construction are less. The following is the 

 description of the foundations for the Ferraby sluice for the 

 Ancholme drainage as given by Sir J. Rennie.j The sluice 

 consists of three openings, each 18 feet wide, and one lock 

 20 feet wide. The sill is 2 feet 6 inches below L.-W. spring 

 tides in the Humber. The soil is alluvial silt and clay. Beech 

 or elm piles, 24 feet long and 12 inches diameter, were driven 

 3 feet apart, centre to centre, all over the site of the founda- 

 tion. The earth was then excavated 2 feet below the pile- 

 heads, and blocks of chalk were well rammed in and grouted 

 with lime and sand. Fir cap-sills and transoms, 12 inches by 

 12 inches, were fixed on the top of the piles, the space 

 between these being filled with brick-work in Roman cement, 

 and the whole covered with Baltic fir three inches thick, 

 fastened down with 9-inch jagged spikes. The flooring was well 

 bedded with lime, puzzolana, and sand. On this floor inverted 

 arches of stone, 18 inches deep at the crown, were built, and 

 the piers and sills erected. On the Humber side an apron 

 was made with piles 16 feet long, the spaces between being 

 filled in with blocks of chalk to a depth of 3 feet, and covered 

 with 3-inch planking. 



* Plate I, Figs. I, 2, 3, 4, for the small sluice, and Plate 2, Figs, i, 2, 3, 4, for 

 the large sluice. 



Trans. Inst. C. E , vol. iv. 



