2 Brief Outline DEFINITION OF PILE CLASSIFICATION OF PILE PILE CAPACITY SETTLEMENT OF PILES AND PILE GROUPLATERAL LOADED PILES (Seismic Consideration)SUMMARY
3 Piles – What?Piles are columnar elements in a foundation which have the function of transferring load from the superstructure through weak compressible strata or through water, onto stiffer or more compact and less compressible soils or onto rock.
4 Piles – When?When the strata at or just below the ground surface is highly compressible and very weak to support the load transmitted by the structure.When the plan of the structure is irregular relative to its outline and load distribution.for the transmission of structural loads through deep water to a firm stratum.to resist horizontal forces in addition to support the vertical loads.when the soil conditions are such that a wash out, erosion or scour of soil may occur from underneath a shallow foundation.To resist uplift forces - transmission towers, off-shore platformsexpansive soils - swell or shrink as the water content changes.Collapsible soils
5 Some ExamplesMultistoried Building Resting on Piles
8 Classification of Piles Based on MaterialSteel Piles, Concrete Piles, Timber Piles, Composite Piles.Based on Load TransferEnd Bearing Piles, Friction Piles, Combined End bearing and Friction PilesBased on Method of InstallationDriven Piles, Driven Cast-in-situ Piles, Bored and Cast-in-situ Piles, Screw Piles, Jacked Piles.Based on UseLoad Bearing Piles, Compaction Piles, Sheet Piles, Fender Piles, Anchor Piles.Based on Displacement of SoilDisplacement Piles, Non-Displacement Piles.
9 Selection of PilesLength of pile in relation to the load and type of soilCharacter of structureAvailability of materialsType of loadingFactors causing deteriorationEase of maintenanceEstimated costs of types of piles, taking into account the initial cost, life expectancy andCost of maintenanceAvailability of funds
12 Types of Failure of Piles Buckling in very weak surrounding soil
13 Types of Failure of Piles General Shear Failure in Strong Lower Soil
14 Types of Failure of Piles Soil of Uniform Strength
15 Types of Failure of Piles Low Strength Soil in Lower Layer, Skin Friction Predominates
16 Types of Failure of Piles Skin Friction in Tension
17 Carrying Capacity of Piles Using Theory (c,φ)Using SPT valueUsing SCPT ValueUsing Dynamic FormulaPile Load TestStatic FormulaIn-situ Penetration Tests
18 STATIC METHOD Qu = Ultimate failure load Qp or Qb = Point (base or tip) resistanceQs = Shaft resistance developed by friction (or adhesion) between the soil and the pile shaft
19 STATIC METHOD FOR DRIVEN PILES IN SAND End Bearing CapacityFrictional ResistanceUltimate Load
20 STATIC METHOD FOR DRIVEN PILES IN CLAY End Bearing CapacityFrictional ResistanceNet Ultimate LoadNet Bearing Capacity
21 Problem 1A concrete pile of 45 cm diameter was driven into sand of loose to medium density to a depth of 15m. The following properties are known:(a) Average unit weight of soil along the length of the pile, y = 17.5 kN/m3 , average φ = 30°,(b) average Ks = 1.0 and δ=Calculate (a) the ultimate bearing capacity of the pile, and (b) the allowable load with Fs = 2.5. Assume the water table is at great depth.
28 Driven Piles - Advantages Piles of any size, length and shape can be made in advance and used at the site. – rapid progress of workDriven into granular soil - compacts the adjacent soil mass - increase in bearing capacityThe work is neat and cleanSupervision of work at the site can be reduced to a minimum.Storage space required is very much less.In places where it is advisable not to drill holes for fear of meeting ground water under pressure.For works over water such as piles in wharf structures or jetties.
29 Driven Piles - Disadvantages Must be properly reinforced to withstand handling stresses during transportation and driving.Advance planning is required for handling and driving.Requires heavy equipment for handling and driving.Since the exact length required at the site cannot be determined in advance, the method involves cutting off extra lengths or adding more lengths - increased cost of projectDriven piles are not suitable in soils of poor drainage qualities – Soil heaving or liftingWhere the foundations of adjacent structures are likely to be affected due to the vibrations generated by the driving of piles, driven piles should not be used.
30 Bored Piles - Advantages Piles of any size and length may be constructed at the site.Damage due to driving and handling that is common in precast piles is eliminated in this case.Ideally suited in places where vibrations of any type are required to be avoided to preserve the safety of the adjoining structure.suitable in soils of poor drainage qualities
31 Bored Piles - Disadvantages Requires careful supervision and quality control of all the materials used in the construction.It needs sufficient storage space for all the materials used in the construction.The advantage of increased bearing capacity due to compaction in granular soil that could be obtained by a driven pile is not produced by a cast-in-situ pile.where there is heavy current of ground water flow or artesian pressure - very difficult to construct
32 Based on SPT Values Displacement piles Bored Piles For H- piles Where Qu ultimate total load in kNNcor average corrected SPT valuebelow pile tipcorrected average SPT value along the pile shaftAb base area of pile in m2(for H-piles including the soil between the flanges)As shaft surface area in m2
33 Bearing Capacity based on SCPT Vander Veen's methodSchmertmann's method
34 Vander Veen’s Method Ultimate load capacity of pile Pile base resistance,Ultimate skin friction