What is the necessity of use pile foundations?

I agree with the previous answers

Thank you sir

1. When the soil is weak and loads irresistible 

When a clay soil be shrinkage and swelling seasonally -2

 when the building above the water surface, such as sidewalks of ports -3

4. When there were neighboring buildings with foundations to close to new building which prevent the foundations excavations of the other kinds of foundations

5 - When requires balancing tensile forces or side pushing forces , called (anchor piles) when installed with vertical position or( batter piles) when installed with oblique position  

6 - In areas where earthquakes occurs frequently  ,  here it distributes in groups touched with each by strengthen ties 

7 - when the groundwater level is high

 I agree with my brother Yaqoob ,,,, The choice of piles depends on the  location and type of structure, the ground conditions, durabilityof the materials and cost. Driven piles are useful in offshore applications, are stable in soft squeezing soils and can densify loose soil. A foundation is described as piled when its depth is more than three times its breadth ,Generally piles are classified as; end-bearing piles (where most of the friction is developed at the toe of the pile, bearing on a hard layer) or friction piles (where most of the pile-bearing capacity is developed by shear stresses along the sides of the pile, suitable when harder layers are too deep). Most piles use some end-bearing and some friction, in order to resist the action of load   However, bored piles are more popular in urban areas as there is minimal vibration, they can be used where headroom is limited, there is no risk of heave and it is easy to vary their length Pile foundations are principally used to transfer the loads from a superstructure, through weak, compressible strata or water onto stronger, more compact, less compressible and stiffer soil or rock at depth, increasing the effective size of a foundation and resisting horizontal loads ).They are used for large structures, and in situations where the soil under is not suitable to prevent excessive settlement.and Very broadly, foundations can be categorised as shallow foundations or deep foundations  . Shallow foundations are typically used where the loads imposed by a structure are low relative to the bearing capacity of the surface soils. Deep foundations are necessary where the bearing capacity of the surface soils is insufficient to support loads imposed and so they are transferred to deeper layers with higher bearing capacity pile foundations are deep foundations. They are formed by long, slender, columnar elements typically made from steel or reinforced concrete and sometimes timber. 

Soil conditions, that speaks for itself,  but also costs and risk, when a shallow foundation is possible, but costly due to groundwater, pending buildings, regulations 

Agree with brother yaqoob 

Totally agree with Mr. Al Omar on the  7  points of necessities of using pile foundations.

Thank you to all my colleagues, I agree and produce an answer, Mr. Yaqoob

i supported answer of Mr.Yakoup and i want to clear that in the water structure the hydraulic profile is the most important so if the suitable soil for foundation is deeper than the required for hydraulic you may be need to make piles foundation   

Pile foundations used when soil bearing capacity is low and couldn't carry the applied loads from the structure, so we go to the strong soil at deep to carry the applied loads. 

If there are cavities in the soil, we canmake rreplacement or go to deep foundation piles. 

Most of piles system are used in high rise building because of heavy load of building. 

Its use when groundwater level is high

1-When the soil SBC < 24

 and Less than applied Load

 2-  Poor quality of upper soil layers

3- When we have expansive soil in construction site4-  To resist uplift forces5-  To resist lateral loads (horizontal)