PILE DESIGN INTRODUCTION

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Nos. of piles needed will depend upon the total vertical load from column / pile capacity 
Pile group of three,four ,five ,six or more can be adopted based on nos of piles required. 
Any moment acting from column is also accounted (as it will effect the exterior piles most) 
by addtional +ve reaction on one side and -ve reaction on other side piles due to moment 

Minimum c/c spacing between piles shall be:   
2*D - - - for piles resting on rock 
2.5*D - - - for piles deriving their strength predominantly from end bearing( predominantly sandy strata) 
3*D - - - for piles deriving their strength predominantly from skin friction( predominantly clayey strata) 

(d= Pile shaft diameter) 

Pile cap can be designed by bending theory .Draw a line at mid depth of   
pile cap .The column load is taken to be dispersed at 45 degrees into 
pile cap upto its mid depth acting downwards.The reaction from piles 
shall also be dispersed at 45 deg upwards upto mid depth line.The BM and 
shear force can be computed at critical sections.Refer IS2911 Part 
1/sec2 on Bored CIS piles 

Critical section for BM is at column face. 
Critical section for shear is at d/2 from column face 
(d- - - is the effective depth of pile cap) 

Clear overhang of pile cap beyond pile shall be 100mm to 150mm . 

Pile cap shall be thick enough for rigidity which helps in distributing 
imposed load on the piles in a group equitably. 

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