Tuesday, October 26, 2010
+The piles are easy to handle.
+Relatively inexpensive where timber is plentiful.
+Sections can be joined together and excess length easily removed.
–The piles will rot above the groundwater level. Have a limited bearing.
–Can easily be damaged during driving by stones and boulders.
–The piles are difﬁcult to splice and are attacked by marine borers in salt water.
Prefabricated concrete piles (reinforced) and prestressed concrete piles affected by the
+Do not corrode or rot.
+Are easy to splice. Relatively inexpensive.
+The quality of the concrete can be checked before driving.
+Stable in squeezing ground, for example, soft clays, silts and peats pile material can be inspected before piling.
+Can be re driven if affected by ground heave. Construction procedure unaffected by groundwater.
+Can be driven in long lengths. Can be carried above ground level, for example, through water for marine structures.
+Can increase the relative density of a granular founding stratum.
–Relatively difﬁcult to cut.
–Displacement, heave, and disturbance of the soil during driving.
–Can be damaged during driving. Replacement piles may be required.
–Sometimes problems with noise and vibration.
–Cannot be driven with very large diameters or in condition of limited headroom.
Driven and cast-in-place concrete piles
Permanently cased (casing left in the ground)
Temporarily cased or uncased (casing retrieved)
+Can be inspected before casting can easily be cut or extended to the desired length.
+Low noise level.
+The piles can be cast before excavation.
+Pile lengths are readily adjustable.
+An enlarged base can be formed which can increase the relative density of a granular founding stratum leading to much higher end bearing capacity.
+Reinforcement is not determined by the effects of handling or driving stresses.
+Can be driven with closed end so excluding the effects of GW.
–Heave of neighboring ground surface, which could lead to re consolidation and the development of negative skin friction forces on piles.
–Displacement of nearby retaining walls. Lifting of previously driven piles, where the penetration at the toe have been sufﬁcient to resist upward movements.
–Tensile damage to unreinforced piles or piles consisting of green concrete, where forces at the toe have been sufﬁcient to resist upward movements.
–Damage piles consisting of uncased or thinly cased green concrete due to the lateral forces set up in the soil, for example, necking or waisting. Concrete cannot be inspected after completion.
Concrete may be weakened if artesian ﬂow pipes up shaft of piles when tube is withdrawn.
–Light steel section or precast concrete shells may be damaged or distorted by hard driving.
–Limitation in length owing to lifting forces required to withdraw casing, nose vibration and ground displacement may be a nuisance or may damage adjacent structures.
–Cannot be driven where headroom is limited.
Bored and cast-in-place (non-displacement piles)
+Length can be readily varied to suit varying ground conditions.
+Soil removed in boring can be inspected and if necessary sampled or in-situ test made.
+Can be installed in very large diameters.
+End enlargement up to two or three diameters is possible in clays.
+Material of piles is not dependent on handling or driving conditions.
+Can be installed in very long lengths.
+Can be installed without appreciable noise or vibrations.
+Can be installed in conditions of very low headroom.
+No risk of ground heave.
–Susceptible to “waisting” or “necking” in squeezing ground.
–Concrete is not placed under ideal conditions and cannot be subsequently inspected.
–Water under artesian pressure may pipe up pile shaft washing out cement.
–Enlarged ends cannot be formed in cohesionless materials without special techniques.
–Cannot be readily extended above ground level especially in river and marine structures.
–Boring methods may loosen sandy or gravely soils requiring base grouting to achieve economical base resistance.
–Sinking piles may cause loss of ground I cohesion-less leading to settlement of adjacent structures.
Steel piles (Rolled steel section)
+The piles are easy to handle and can easily be cut to desired length.
+Can be driven through dense layers. The lateral displacement of the soil during driving is low (steel section H or I section piles) can be relatively easily spliced or bolted.
+Can be driven hard and in very long lengths.
+Can carry heavy loads.
+Can be successfully anchored in sloping rock.
+Small displacement piles particularly useful if ground displacements and disturbance critical.
–The piles will corrode.
–Will deviate relatively easily during driving.
–Are relatively expensive.