Lecture 25 :
Pile Groups [ Section 25.3 :
Design value of ultimate load ; Settlement of a pile ]
Design value of ultimate load
For piled raft foundation : The minimum of block failure value and the sum of individual pile capacities.
For free standing pile : The minimum of block failure value and 2/3 rd the sum of individual pile capacities.
Minimum of block failure value & 2/3 of sum of individual pile capacity
Bearing capacity of block plus bearing capacity of
1.
Extra width of pile group and times bearing capacity of each pile + bearing capacity of ( area of cap – area of pile, n)
2.
---------(46)
where is the value at cap base, is the cohesion, and , are width and length of cap
Settlement of a pile
At centre of pile,
---------(47)
where p is the perimeter of the pile and a is the radius from centre of the pile
In reality, settlement of a single pile is,
where w is the total settlement, is the settlement due to axial deformation of pile shaft because of pile material, is the settlement of a pile tip or point due to load transmitted along pile shaft, and is the settlement pile tip due to load transmitted at pile tip.
is the 
value at cap base, 
is the cohesion, and 
, 
are width and length of cap 
is the settlement due to axial deformation of pile shaft because of pile material, 
is the settlement of a pile tip or point due to load transmitted along pile shaft, and 
is the settlement pile tip due to load transmitted at pile tip. 
