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Pile Construction and Testing TechniquesGroup MembersTanveer Younas (2015-MS-CES-24)Atta Muhammad (2013-MS-CES-27)ContentsIntroduction to PilesFunction of PilesTypes of PilesConstruction Techniques for PilingComparison of Different PilesProblems in pile construction and remedial measuresTesting Techniques in PilesConclusion

Introduction to PilesDefinitionA pile is a vertical structural element of a deep foundation, driven deep into the ground at the building site.

For Deep Foundations Df/B > 4Pile foundation- need and functionsPile foundation is required when the soil bearing capacity is not sufficient for the structure to withstand.

This is due to the soil condition or the order of bottom layers, type of loads on foundations, conditions at site and operational conditions.

Pile foundation- need and functions (cont.)Purpose of pile foundation is To transmit the buildings loads to the foundations and the ground soil layers whether these loads vertical or inclined.To install loose cohesion less soil through displacement and vibration.To control the settlements.To increase the factor of safety for heavy loads buildings

Types of PilesPiles are classified on the basis ofMaterial of constructionType of soilLoad transmitting characteristicsConstruction methodW.r.t material of construction, piles areTimber PilesSteel PilesConcrete Piles

Types of PilesOnce soil data is obtained from soil exploration boreholes at different depths, selection of pile foundation type depends upon following factors.Soil conditionsNature of loadsNumber of piles to be usedCost of constructionTypes of Piles (cont.)There are three types of piles based upon load transfer mechanism End bearing pilesFriction bearing pilesCombination of end bearing and friction bearing piles.Types of Piles (cont.) Based upon construction techniques, piles may be classified intoDriven pilesCast-in-situ pilesDriven and cast-in-situ piles.Pile installation methodsThe installation process and method of installations are equally important factors as of the design process of pile foundations. pile installation methods areInstallation by pile hammerInstallation by mechanical augerIn order to avoid damages to the piles, during design, installation Methods and installation equipment should be carefully selected.

Pile driving methods Methods of pile driving can be categorized as follow:Dropping weightExplosionVibrationJacking (restricted to micro-piling)JettingDriven piles vs. jetted piles, a comparisonIn case of driven piles, hard soils may offer sufficient resistance to penetration of pile making the action of pile driving difficult.In such situation, jetting may be used.Pile jetting is a technique that is frequently used in conjunction with, or separate from, pile driving equipment for pile placement.Pile jetting utilizes a carefully directed and pressurized flow of water to assist in pile placement

Driven piles vs. jetted piles, a comparison (cont.)Pile jettingLiquefies the soil at the pile tip during pile placementreduces the friction and interlocking between adjactant sub-grade soil particles around the jet.Thus, decreases the bearing capacity of soil underneath the pile tip, pile descends easily under its own weight.

Problems in pile construction and remedial measuresDifferent problems may occur during pile construction.Overbreak Formation of cavities outside nominal diameter of pile is known as over break.It may occur in cohesion less soils below water tableReduced skin friction and end bearing.

Overbreak (cont.)Measure:It may be overcome by using temporary casing or drilling under bentonite drilling fluid.

OverbreakBase of BoreholeTo develop available end bearing, It is essential that bottom of borehole is clean and undisturbed.In clayey soilsIn sandy soilsMeasure: To avoid falling of debris, cover the borehole properly before concreting.

Effect of water table In dry drilling of borehole, ingress of small quantity of water from sides of borehole reducesSkin frictionBearing from bottom of boreholeMeasure:In this condition, concreting should be carried out with tremmie pipe otherwise, segregation of concrete may occur.Design of ReinforcementMajor problem in design of pile reinforcement is its detailing. A minimum spacing of 100mm is required otherwise, concrete will not flow outside the cage and proper cover could not be provided.A few large diameter bars are preferred in place of small diameter bars.The problem is visible during concreting when cage drags downward into the borehole.

Lowering of ReinforcementSteel cage should be lowered after providing proper laps so that there is no slippage of cage while lowering.When weight of cage is more in deep piles, cage should be welded at the laps before lowering.

Lowering of Reinforcement

Steel cage properly welded and lapped before loweringPlacing of ConcreteConcrete is placed in borehole using tremmie in order to avoid segregationConcreting process should be continuous and should be completed without any breakIf slight delay occurs between batches then cement slurry may come over surface causing weakness of pile shaft.If prolonged delay occurs between batches then concrete may approach final setting time.

Extracting temporary casingAfter concreting, extraction of temporary casing may cause problems particularly if delays occur and partial separation of pile shaft may occur.This is due toUse of dirty and dented casingDelay in extractingUse of poor workable mixExtracting temporary casing

Faulty removal of casingProblems in soft groundIn soft ground having undrained shear strength less than 15 KN/m2 causing squeezing of pile section near the head because lateral pressure of soil is more than the lateral pressure of concrete.

Squeezing of section in soft groundTesting techniques in pilesThe success of piling depends upon the load carrying capacity and integrity of pile. If one can somehow, find the load carrying capacity and integrity of pile then the performance of piling can be understood in a better way.Testing techniques in piles (cont.)These days, with the invent of modern computers different modern methods of pile testing have been devised which give more reliable information regarding the load carrying capacity and integrity of pile.Some methods of pile testing are being enlisted here.

Testing techniques in piles (cont.)Static load methodDynamic load methodSonic integrity method

Testing techniques in piles (cont.)Static Load Method Static load testing is the method by which the load displacement characteristics of a pile can be determined. All piles are suited to testing in this way.DescriptionIn order to apply a known load to the test pile some form of reaction is necessary

Static load MethodThe most commonly used methods are Kent ledge or tension pile reaction, dependent upon ground conditions. Other methodologies can be adopted according to site requirements e.g. in areas of restricted access or headroom.Once adequate reaction has been provided, the testing is carried out using a hydraulic jack and calibrated digital load cell to a previously agreed procedure. Static load Method (cont.)Time, load, temperature and displacement data are usually recorded.Reaction loading frames and Kent ledge assemblies allow tests of up to 4000kN to be carried out. Measurement of pile response to load is measured by digital load cells and electronic linear variable displacement transducers.Static load Method (cont.)

Pile head measurement at Abingdon, OxfordKent ledge test-frame on site at Belvedere, South LondonDynamic load MethodDynamic load testing is suitable for all types of piles, but is mostly employed on pre-cast concreteThis technique determines load bearing characteristics of pile including skin friction and end bearing.Pile integrity, pile stresses, driving and load displacement behavior can also be determined.Dynamic load Method (cont.)DescriptionIn order to dynamically test a pile, pile must be restruck using a pile hammer.Two strain transducers and accelerometers are firmly attached to the face of pile near to head.As pile is restruck, instrument measures the force and acceleration of pile.This information is relayed to pile driving analyser which gives information about pile capacity to an experienced test operator.Dynamic load Method (cont.)As test takes a few minutes per pile so, a number of piles may be tested in one visit.The aim of method is to produce a model that resembles as closely as possible to a model which is truly replica of recorded data.Once this has been achieved the model gives bearing capacity, load settlement behavior together with additional information as required.

Dynamic load Method (cont.)

Pile prepared for testing on sitePile driving analyzer for collection and analysis of test dataSonic integrity testIntegrity testing is primarily used on continuous flight auger (CFA) or RB continuous helical displacement (CHD) and other wet bored piling techniques.The method is fast and reliable, allowing a large number of piles to be tested in a single site visit. The technique is used to determine the reliability, morphology and quality of construction of the piling method.Sonic integrity testDescriptionThe pile to be tested must be sufficiently cured, free of latence and trimmed to sound concrete, preferably to final cut-off level. Using a small hand-held hammer, a series of low strain acoustic shock waves are passed down the pile. As it does so, the wave rebounds where changes in impedance occur. This rebound or echo is then recorded by a small accelerometer, held against the pile head.

Sonic integrity test The response is stored digitally and a graphical representation displayed and plotted, usually against time, for immediate inspection.

Sonic integrity testing equipmentStatic & Dynamic testing of piles A case-studyThis case study was done by S.Abe , G.Likins and C.M. MorganoTraditionally, static methods were used for pile testing, which now-a-days are being replaced by dynamic testing as this case study depicts.As a part of deep foundation institute program in North Carolina, a demonstration of pile driving and pile testing was performed.

Static & Dynamic testing of piles A case-studyA 305mm prestressed pile of length 16.5m was driven into sandy and clayey silts by a conmaco 65E5 hammer to a final penetration resistance of 5blows/inch.Upon restrike, three days later resistance increased to 10 blows/25mm indicating soil setup. On a WEAP bearing graph,restrike blow count indicated that capacity came out to be 1735 KN (390 kips).Static & Dynamic testing of piles A case-studyThen pile was tested dynamically using a pile driving analyzer and results were further analyzed by CAPWAP method.This analysis indicated a capacity of 1870 KN (420 kips).After that a static test was performed using ASTM D-1143, pile was loaded to maximum load of 1840KN and had a davisson offset limit load of 1820 KN.Static & Dynamic testing of piles A case-study

ConclusionFor pile construction, an experienced engineer is required who can tackle the problems at site in the most effective way.A good supervision at the site is required in order to maintain better performance of piling.A suitable test is to be devised as per site conditions, sensitivity of the project and economy available.