Deep Foundation and classification

 

Deep Foundation: A deep foundation is a type of foundation that transfers building loads to the earth farther down from the surface than a shallow foundation does to a subsurface layer or a range of depths. A pile or piling is a vertical structural element of a deep foundation, driven or drilled deep into the ground at the building site.

The  most common forms of construction pertaining to  deep foundations are:

(a)Pile

(b)Cofferdams

(c)Caissons

   Pile foundation:  Pile foundation is generally used when simple spread foundation at a suitable depth is not possible either because the stratum of required bearing capacity is at a greater depth or steep slopes are encountered.

 Type of Piles: Depending upon their function or use pile may be classified into the following types:

1.      Bearing piles

2.      Friction piles

3.      Sheet piles

4.      Anchor piles

5.      Batter piles

6.      Fender piles

7.      Compaction piles

Classification of piles: Depending upon  the material used in their manufacture, piles  can be broadly classified as:

1.      Timber Piles

2.      Concrete piles

3.      Composite Piles

4.      Steel Piles

Timber Piles: Transmission Of load though timber piles takes by the frictional resistance of the ground and the pile surface.Timber piles prove economical for supporting light structures to be located in compressive soils constantly saturated with water.

Concrete Piles: Concrete piles may be classified as:

1.      Pre-cast piles

2.      Cast in place or cast-in-situ pile

3.      Pre-stressed Concrete pile

 Pre-cast pile: Pre-c cast pile may be define as a reinforced concrete pile which is moulded in circular, square, rectangular or octagonal form. The pile are cast and cured yard and then transported to the site for driving .In case space is available,pile can be cast and cured near the site of works.

Cast–in–situ-pile: Cast in situ pile are those pile which are cast in position inside the ground. Since the pile is not subjected to handling or driving stress, it is not necessary to reinforce the pile in ordinary case or in places where the pile is completely submerged in the soil.

Types of Cast in situ piles:

The biggest disadvantage of pre-cast pile is their large weight. The precast pile is reinforced to take care of the handling and driving stresses rather than to strengthen the pile to act as a column .In some case the handling stresses are anticipated to be so severe that the pile has to  be lifted at a number of points to be able to withstand the handling stresses.

 

Composite Piles:This is a type of construction in which piles of two different materials are driven one over the other,so as to enable then to act together to perform the function of a single pile. In such a combination, advantage is taken of the good qualities of both the materials. Composite pile proven economical as they permit the utilization of the corrosion resistance property of one material with the cheapness or strength of the other.

Steel pile: 

(a) H-piles:The use of rolled steel H- beams to function as bearing piles is a comparatively recent development in piling industry. H-pile can withstrand large impact stresses developed during hard driving.

(b)Pipe-piles:Seamless or welded steel pipes are often driven to function as end bearing or friction piles.The pipe piles may be driven either open ended or close ended.

(c)Screw piles:A screw pile consists of a cast iron or steel shaft of exfernal diameter normally  varying form 15 to 30 cm and terminating into a helix or screw base.

(d)Dise piles. Similar to a screw pile consists of hollow metallic pipe attached with a cast iron dise to its foot so as to enlarge the bearing area of the pile.