286 Wisconsin Academy of /Sciences, Arts^ and Letters. 



the weight of the ram in pounds, the product will be the weight 

 the pile can bear with safety. 



Ex(h-^z)v , 



Mithel's screw piles have been used with good success ; they 

 consist of iron piles in sections of desirable length, the bottom 

 section having one turn of a broad iron screw ; these are forced 

 into the ground by turning them around by means of levers 

 moved by man or horse power. The government of Grreat Britain 

 has built a number of bridges in India upon screw pile piers, 

 which have all been successful. 



The screw cylinder I consider a great improvement over the 

 screw pile. The cylinder is made of cast iron of convenient 

 lengths ; the lower section is provided with a screw on the outside, 

 of a foot or more in width, the sections are screwed and bolted to- 

 gether by flanges on the inside ; the earth is removed from the 

 inside by suitable implements as fast as the cylinder progresses. 

 The cylinder is afterwards filled with concrete. 



The Triger system of foundations (so named from its inventor) 

 and largely improved and applied by Mr. Hughes in England, is 

 in reality an enlared hollow pile, and ultimately led to the use of 

 very large cylinders and caissons. I present herewith a plan of 

 an iron centre-pier for a swing bridge, the process of the opera- 

 tion of lowering, excavating, under pinning and filling is shown 

 in the drawings. The centre pier of the iron swing bridge over 

 the Harlem river at New York was constructed in this manner by 

 Mr. McAlpin. There was one central and nine circuhiscribing 

 cylinders of six feet diameter, these were put down from 60 to 80 

 feet until the bottom was considered sufficiently resisting to bear 

 the great weight. When the cylinders came to rest, the base was 

 enlarged four feet in all directions, this increased the resisting area 

 to forty-nine as against nine without this precaution. 



If there is much trouble from leakwater, the Plenum and 

 Vacuum process may be applied by putting an airlock on the top 

 of the cylinder and forcing in air under sufficient pressure to expel 

 the water. When the excavation has proceeded as far as possi- 

 ble, the process is reversed and the air exhausted, the atmospheric 

 pressure will then force the cylinder onward. 



