DEEP FOUNDATION ANALYSIS AND DESIGN

although spread footing are the most common type of foundation, engineer often encounter circumstance where other types are more approviate. example the following :

the upper soils are so weak and or the structural
loads so high that spread footings would be to
large. a good rule of thumb for building is that
spread footings cease to be economical when the
total plan area of the footings exceeds one half of
the building footprint area.
the upper soil are subject to scour or
undermining. this would be especially of concem
with midstream foundations for bridge.
the foundations must penetrete though water
a large uplift capacity is required ( the uplift
capacity of a spread footing is limited to its
dead weoght)

in some of these circumstance, a mat foundation my be appropiate, but the most common alternative to spread footing is some type of deep foundation.
A deep foundation is one that transmits some or all of the applied load soil well below the ground surface, this foundations typically extend to depths on the order of 50 ft ( 15 m) below the ground surface, but they can be much longer, perhaps extending as deep as 150 ft ( 45 m). even greater lenghts have been used in some offshore structures, such as soil drilling platforms. since soils usually improve with depth, and this methode mobilizes a larger volume of soil, deep foundations are often able to carry very large loads.

1.CLASIFICATION OF DEEP FOUNDATIONS

   Engineers and contractors have developed many 
   kinds of deep foundations, each of which is best 
   suited to certain loading and soil conditions. 
   unfortunately, people use many different names 
   to identify these design, different individuals often 
   use the same terms to mean different things and 
   different terms to means the same thing. 
   appear  to be most common in north america.
   other term and alternative difnitions are in 
   appendix

we will divide deeo foundations in to three broad group, as show in figure

TRANSFERRING AXIAL LOADS THE GROUND

3.CONSTUCTION METHODS AND EQUIPMENT

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