Write short Notes on Classification Of Piles

Classification of piles: Piles can be classified on the basis of:-

A.    Material Used

B.     Mode of Transfer

C.     The method of  installation

D.    Uses

A.    On the basis of material used

                                           I.            Steel Piles :- Steel piles are usually of the rolled H sections or thick pipe sections. This Piles are used to withstand large impact stresses and where fewer disturbances from driving is desired. They are usually driven with open ends into the soil. A conical tip is used where the piles have to penetrate boulders and rocks.

                                        II.            Cement concrete Piles:- Cement Concrete piles are either precast or cast in-situ. Precast piles are cast and cured at the casting yard and then transported to the site for installation. These piles are adequately reinforced to withstand handling stresses along with working stress. Precast piles are generally used for short lengths. Cast-in-situ piles are constructed by drilling hole in the ground and then filling that hole with freshly prepared concrete after placing the reinforcement.

                                     III.            Timber Piles :-Timber piles are made from tree trunks and are well seasoned, straight and free from all defects. Usually available length will be 4 to 6m. Timber piles are used where good bearing stratum is available at a relatively shallow depth.

                                     IV.            Composite Piles:- A pile made up of two or more than two different materials like concrete and timber or concrete and steel is called composite pile. Composite piles are mainly used where a part of the pile is permanently under water. The part of the pile which will be under water can be made of untreated timber and the other part can be of concrete.

B.     On the basis of mode of transfer of load

                                                       I.            Bearing Piles:-Piles which transfer structural load to a hard and relatively incompressible stratum such as rock or dense sand are known as bearing piles. These piles derive the required bearing capacity from end bearing at tip of the pile. The bottom end of the pile rests on a layer of especially strong soil or rock. The key principle is that the bottom end rests on the surface which is the intersection of a weak and strong layer. The load therefore bypasses the weak layer and is Safely transferred to the strong layer.

                                                    II.            Frictional Piles:-These are piles which derive carrying capacity from skin friction or adhesion between the pile surface and surrounding soil. In other words, the entire surface of the pile, which is cylindrical in shape, works to transfer the forces to the soil. It is used to deep beds of clay and silt where deep hard stratum is very great. They do not reach to the hard stratum.

                                                 III.            Combined end bearing and friction Piles:-The pile in which end bearing pile at the bottom and friction along the surface of pile shaft combined together acting as a single unit is called combined end bearing and friction piles.

C.     On the basis of method of installation

                                                       I.            Driven Piles :- Driven piles may be of concrete, steel or timber. These piles are driven into the soil strata by the impact of a hammer. Generally boring is not used in these cases.

                                                    II.            Bored Piles :- Bored piles are constructed in pre-bored holes either using a casing or by circulating stabilizing agent like bentonite slurry. The borehole is filled with concrete after placing or lowering reinforcement. The main advantage in bored piles is no damage due to handling and driving which is common in driven piles.

                                                 III.            Driven and cast-in-situ piles:- These piles are formed by driving a tube with a closed bottom end into the soil strata, and then filling the tube with freshly prepared concrete.

                                                 IV.            Screw Piles:- These piles are screwed in to the soil.

                                                    V.            Jacked Piles:-Jacked into the soil by applying downward force with the help of hydraulic jack.

D.    On the basis of Uses

                                                       I.            Compaction Piles:-These piles are used to compact loose granular soil to increase its bearing capacity. Compaction piles do not carry load and hence they can be of weaker material. Sand piles can be used as compaction Piles.

                                                    II.            Tension Piles:-These piles are also called as uplift piles. Generally it can be used to anchor down the structures which are subjected to uplift pressure due to hydrostatic force.

                                                 III.            Anchor Piles:-These piles are generally used to provide anchorage against horizontal pull.

                                                 IV.            Fender Piles:-Fender piles are used to protect water front structure from impact of any floating  object such as ships and vessels.