Pile Installation

8/11/2019 Pile Installation

1/18

1.1 PILE INSTALLATION

1.1.1 INTRODUCTION

There are uncertainties in the design of piles due to the inherent variability of the

ground conditions and the potential effects of the construction process on pileperformance. Test driving may be considered at the start of a driven pilingcontract to assess the expected driving characteristics.

Adequate supervision must be provided to ensure the agreed constructionmethod is followed and enable an assessment of the actual ground conditions tobe carried out during construction. It is necessary to verify that the designassumptions are reasonable.

Foundation construction is usually on the critical path and the costs and timedelay associated with investigating and rectifying defective piles could be

considerable. It is therefore essential that pile construction is closely supervisedby suitably qualified and experienced personnel who fully understand theassumptions on which the design is based.Detailed construction records must be kept as these can be used to identifypotential defects and diagnose problems in the works.

1.1.2 MATERIALS AND EQUIPMENTS

1.1.2.1 Types of Pile Driving Machines

Drop Hammer

Single Acting Hammer

Double Acting Hammer

Hydraulic Drop Hammer

Diesel Hammer

Vibratory Hammer

Hydraulic Injection Pile

TYPES OF PILE DRIVING MACHINES


2/18

1.1.2.1.1 Drop Hammer

Figure 1: Drop Hammer

A hammer with approximately the weight of the pile is raised a suitableheight in a guide and released to strike the pile head.

A simple form of hammer used in conjunction with light frame and testpiling where it may be uneconomical to bring a steam boiler orcompressor on to site to drive very limited number of piles.

There are two types of drop hammer which is single acting steam orcompressed air hammer and double acting pile hammer.

1.1.2.1.2 Single Acting Hammer

Figure 2: Single Acting Hammer


3/18

Activated by steam or air pressure

Hammer fall as the force of gravity

The energy produced is usually 10-2250 kN.m

35-60 operations per minute rate blow.

The advantages of consistent operating shock rate that is higher than thedrop.

1.1.2.1.3 Double Acting Hammer

The striking ram (piston) is driven bycompressed air or steam when rising andfalling.

The air or steam arrives under pressure in avalve box containing a slide valve whichsends it alternately to each side of the piston,while the opposite side is connected to theexhaust ports.

When falling, the striking mass hits a flat anvilfixed to the cylinder resting on top of thesheet pile being driven. Then the pressure

lifts the piston and allows it to be forced downagain on to the anvil.

Overall weight the ram is much less than thatof the drop hammer.

The hammers a designed to operate atmaximum efficiency when used with standardsizes of compressors normally available.

Figure 3: Double-acting

air hammer


4/18

It is not advisable to insert a driving cap between the hammer anvil andthe sheet pile being driven since this leads to an enormous loss ofefficiency.

Can also be equipped to operate under water and for the extraction ofpiles.

1.1.2.1.4 Hydraulic Drop Hammer

Figure 4: Hydraulic Drop Hammer

A hydraulic drop hammer is a modern type of piling hammer used inplace of diesel and air hammers for driving steel pipe, precast concrete,and timber piles.

Hydraulic drop hammers are more environmentally acceptable than theolder, less efficient hammers as they generate less noise and pollutants.

However, in many cases the dominant noise is caused by the impact ofthe hammer on the pile, or the impacts between components of thehammer, so that the resulting noise level can be very similar to dieselhammers.

1.1.2.1.5 Diesel Hammer


5/18

Figure 5: Diesel Hammer

Rapid controlled explosions can be produced by the diesel hammer.

The explosions raise a ram which is used to drive the pile into theground.

Although the ram is smaller than the weight used in the drop hammer,the increased frequency of the blows can make up for this inefficiency.

This type of hammer is most suitable for driving piles through non-cohesive granular soils where the majority of the resistance is from endbearing.

1.1.2.1.6 Vibratory Hammer


6/18

Figure 6: Vibratory Hammer

Vibratory methods can prove to be very effective in driving piles throughnon cohesive granular soils.

The vibration of the pile excites the soil grains adjacent to the pilemaking the soil almost free flowing thus significantly reducing frictionalong the pile shaft.

The vibration can be produced by electrically (or hydraulically) poweredcontra-rotating eccentric masses attached to the pile head usually actingat a frequency of about 20-40 Hz.

If this frequency is increased to around 100 Hz it can set up alongitudinal resonance in the pile and penetration rates can approach up

to 20 m/min in moderately dense granular soils. However the large energy resulting from the vibrations can damage

equipment, noise and vibration propagation can also result in thesettlement of nearby buildings.


7/18

1.1.2.1.7 Hydraulic Jack- In Pile

Figure 7: Hydraulic Jack-In Pile

Noise- and vibration-free, no mud slurry, no excavated material to bedisposed.

Sound quality compared to bored piles, as piles are pre-cast andinstalled by jacking in.

No hard driving, no uncertainty of in-situ underground concrete casting.

Much faster than construction of bored piles.

Capacity of each pile installed is verified by a jack-in force up to twotimes design loads (DL) or higher.

Obstructions in the dump material as mentioned above are not aconcern.

When a pile is jacked under a force of 2DL or higher, the obstacles willbe pushed aside or dragged all the way down to bearing stratum orbedrock (In the latter case, the decaying of the material might be aconcern.).


8/18

1.1.2.2 Pile Driving Equipment

Figure 8: Driving Pile Equipment

1.1.2.2.1 Leads

Leads are generally a box shaped frame used to align the pile and hammerduring driving and must be long enough to accommodate the length of the pile

segments, the hammer, and other equipment as required for the project.Types of leads include swinging, fixed, or semi-fixed leads depending uponthe connection between the leads and the crane. Swinging leads tend to bethe most popular and are generally suspended from the crane boom by acable and are required by the Standard Specifications to be toed into theground to assist with alignment of the pile during driving.

1.1.2.2.2 Hammers

Hammers are used to advance the piling into the ground to the nominalrequired bearing indicated in the plans.


9/18

Figure 9: Hammer Components Illustration

1.1.2.2.3 Hammer Components

The figure below illustrates the various hammer components that are typicallyused at the top of the pile.

A drive head, also referred to as a helmet or cap, is provided to protect the topof the pile and assist in holding the pile in line with the hammer. The StandardSpecifications require that the drive cap be made from cast or structural steeland that it also serve as a pilot for metal shell piles uniformly distributing the

hammer energy across the metal shell cross section.

Cushions are sometimes used above and below the drive head to protect thehammer and the pile and dampen the intensity of the hammer blow. Cushionsused above the drive head are referred to as hammer cushions while cushionsused below the drive head are referred to as pile cushions.Timber and concrete piles are required by the Standard Specifications to beprotected with a pile cushion.

Hammer cushions may be made from a variety of materials including wirerope, polymer, aluminum, or steel. Pile cushions have traditionally been made

from plywood. Cushions wear and require replacement periodically throughoutthe pile driving process. Pile cushions should be replaced when the reductionin thickness is greater than 40% or they begin to burn. Hammer cushionsshould be replaced after each 50 hours of operation, when there is a reductionin thickness in excess of 25% or the manufacturers limitations.


10/18

1.2 LOAD TESTS ON PILE

1.2.1 INTRODUCTION

Pile load tests carried out on randomly selected actual piles to check the pile

design capacities. Three types of tests have been recommended which are StaticLoad Test or Maintained Load Test (MLT), Constant Rate of Penetration (CRP)and Pile Dynamic Analyzer (PDA)

Pile load test are usually carried out that one or some of the following reasonsare fulfilled:

To obtain back-figured soil data that will enable other piles to bedesigned.

To confirm pile lengths and hence contract costs before the client iscommitted to overall job costs.

To counter-check results from geotechnical and pile driving formulae. To determine the load-settlement behavior of a pile especially in the

region of the anticipated working load that the data can be used inprediction of group settlement.

To verify structural soundness of the pile.

1.2.1.1 Constant Rate of Penetration (CRP)

The equipment used is the same as that used in the maintained load test.

1.2.1.1.1 Function

The pile is made to penetrate the soil at a constant speed. This isachieved by increasing the applied force. The force applied to the headof the pile to maintain this constant rate of penetration varies and ismeasured continuously. As a result of the pile movement, the soil isstressed progressively until it fails in shear. When this occurs, theultimate bearing capacity of the pile is reached.

1.2.1.1.2 Method of Loading

a. Before the test is begun, the hydraulic jack and the load cell are

inserted between the pile head and the reaction system.b. The jack is then operated to cause the pile to penetrate the soil at a

uniform speed.c. Readings of time, penetrate rate and jacking force are made at

convenient intervals. A penetration rate of about 0.75 mm/min. is asuitable choice for friction piles in clay, while a penetration rate ofabout 1.5 mm/min. is a suitable choice for end bearing piles in sand


11/18

or gravel. However, the actual rate may vary depending on thepumping equipment available.

The test usually proceeds very rapidly and requires the services of severalobservers to take simultaneous readings.

For a predominantly end bearing pile, the ultimate bearing capacity inmost cases is taken as the force at which the penetration is equal to 10percent of the base diameter of the pile. However, two factors that shouldbe borne in mind are:

i. for a very long pile, the elastic shortening of the pile during the testmay reach 10 percent of the base diameter: and

ii. for a large pile, there may be difficulty in loading the pile to asettlement as great as 10 percent of its base diameter.

Figure In the cases of where compression tests are being carried out, thefollowing methods are usually employed to apply the load or downwardforce on the pile:

Figure 10: CRP Test

ADVANTAGES DISADVANTAGES

Suits all pile types Reaction piles/kentledge andframe required.

Manual and automatedsystems available.

Kentledge tests are relativelyexpensive.

Limited to cohesive soils. May over predict ultimate load.


12/18

1.2.1.2 Maintained Increment Load Test (MLT)

Figure 11: MLT Test

The performance of the test pile shall be deemed to have satisfied therequirement of the specification, if the settlement /deflection of the pile head atvarious stage of loading in Maintained Load test complies with the specificationrequirement given below:

1) When residual settlement after removal of test load shall not exceed6.50mm.

2) When total settlement under working load shall not exceed 12.50mm or 10% of the pile diameter, whichever is lower value.

3) When total settlement under twice working load shall not exceed 38.0mm or10% of pile diameter, whichever is lower value.

1.2.1.2.1 Scope

The test is applied by means of a jack,which obtains its reaction from aproperty stacked kentledge comprisingprecast concrete blocks. The totalweight of the kentledge shall be

greater than the required test load and shallbe placed on a platform supported well clearof the test pile.


13/18

1.2.1.2.2 ConstructionProcedure

1.2.1.2.2.1 Pile Preparation after Completion of Driving

After the test pile has been driven to set, it will be left for 5 daysbefore placing of the static load. During this time, the pile headwill be trimmed or the surrounding ground level reduced to allowthe pile head to project. The pile head will be thoroughly cleanedand capped with non-shrink grout to ensure a firm bearingsurface perpendicular to the pile axis.

1.2.1.2.2.2 Installation of Jack, Load Frame and Kentledge

The hydraulic jack is placed onto the pile head with a steelpacker plate between the jack and the pile head. The ram of the

jack should be adjusted until it is projecting. The settlementmonitoring frame is next mounted to the pile head- this frame willbe made of steel channels tied together around the pile headwith two tie rods and bolts as detailed in Sketch SLT 1 below. 4reaction legs (steel tube) are driven into the ground adjacent tothe ends of the channels and a concrete plug placed aroundeach leg for additional stability. These legs will have small steelplates welded horizontally to the top once installed. Thesettlement gauges will be fitted to the ends of the channels andthe gauge measurement arm will rest against the individual leg.Settlement gauges will only be installed after the load frame andkentledge have been placed, as described below.

The load frame can now be installeddirectly over the jack with the jackingbeam set higher than the ram. Theload frame will be supported on theoutside by two lines of concreteblocks as detailed in Sketch SLT 1below. The kentledge blocks are nowloaded individually onto the frameusing a cranethis should be done toensure that the load is evenlydistributed at all-time i.e. the entire

frame is laoded with the first layer ofconcrete blocks before the secondlayer is started, the second layer isfinished before the third layer is

started, etc. This will ensure that the kentledge load is stable atall times and will allow safe access for all personnel. This loadingprocedure will continue until the entire kentledge has beeninstalled.
http://2.bp.blogspot.com/-0f0WeLN1eIA/T75SMyDaUSI/AAAAAAAABEI/Z4WQmlvoJMI/s1600/MLT+1.jpg


14/18

Once completed, the kentledge should be left for a settling periodof 24 hours. The 4 settlement gauges are next installed at eachend of the channels with their measurement arms projectingvertically downwards.

This measuring arm shall rest against a plate of glass resting ontop of the steel leg. Any gap between the jack ram and thebearing plate at the base of the jacking beam should first beclosed with a steel packing plate this will ensure that there isstill sufficient stroke in the ram to load the pile to the full test load.The jack ram is now extended to the point where the load gaugestarts to rise each settlement gauge is zeroed, the readingrecorded and the static load test can be commenced.

Figure 12: Incremental Loading and the Monitoring of Displacement
http://2.bp.blogspot.com/-0OOtrouz7rw/T75M3ZbwgDI/AAAAAAAABDc/ax4w8i3YClk/s1600/DSCN1387.JPGhttp://4.bp.blogspot.com/-pBpZzTNPtSc/T75MtbVUc_I/AAAAAAAABDE/UzPm5Tpl_ZE/s1600/DSCN1378.JPGhttp://2.bp.blogspot.com/-0OOtrouz7rw/T75M3ZbwgDI/AAAAAAAABDc/ax4w8i3YClk/s1600/DSCN1387.JPGhttp://4.bp.blogspot.com/-pBpZzTNPtSc/T75MtbVUc_I/AAAAAAAABDE/UzPm5Tpl_ZE/s1600/DSCN1378.JPG


15/18

The pile is now loaded according to the incremental sustainedload test method as defined by the Designer.

A datum should be established on a permanent object or otherwell founded structure which shall not be disturbed by the test

loading or other operation on the site.

The entire test area must be sheltered from direct sunlight, wind,rain and be sufficiently lighted during the night to facilitate takingreadings.

The monitoring of the displacement will be done by applying thejack load up to the specified load, immediately recording thesettlement reading, re-recording the settlement (whereappropriate) at specified time interval after reaching load andalso immediately prior to any change in load. The same

procedure would be followed for the next load state.

Once the test has been completed, the jack ram will bewithdrawn and the load frame with kentledge will be removed.

Maintained load test results shall be recorded for further analysisby consultant.

Figure 13: Assessment of Settlement Figures

Before the removal of the kentledge and load frame, thesettlements will be analyzed according to design requirement.Should the measured settlement figures be within the limits, thepile will be considered as having passed the maintained loadtest.
http://4.bp.blogspot.com/-Jlw1yWBZ0n0/T75Mp9G8chI/AAAAAAAABC8/kx-iJF05VbU/s1600/DSCN1376.JPG


16/18

1.2.1.3 Pile Dynamic Analyzer (PDA) or Dynamic Load Test (DLT)

1.2.1.3.1 Purpose

A quick method to evaluate the bearing capacity of piles for

loads similar to the design load. It can be used for pre-fabricated piles, cast-in-place concrete

piles, steel piles and wooden piles.

PDA is considerably faster than static test and at a fraction of thecost.

1.2.1.3.2 Conducting a PDA/DLT

Adequate time should be allowed for soil stabilization before testing. Toprepare for a PDA, sensors are connected to the pile near the pilehead. These sensors have combined function; to measure strain and

acceleration.

On concrete piles, the sensors are connected to the pile with anchorbolts. On steel piles, the sensors are bolted to the pile using threadedholes or welded mounting blocks. Special sensors for underwater useare also available. All sensors are may be recovered after testing. Oncethe sensors have been connected to the PDA monitoring system, thissystem can be to use to direct the test controls.

To apply a load, an impact ram or a heavy block (drop hammer) isdropped onto specially prepared pile head. The generated compression

wave travels down the pile and reflects from the pile toe upward. Thisreflected wave contains information about the shaft friction, toeresistances and pile defects. The measured signals are processed andautomatically stored by the PDA monitoring system. The data can beretrieved easily for further review, graphical presentation or reporting.

PDA is most suitable for driven piles. For cast-in-place piles, it may beimpossible to generate the required loads, or the stresses can becometoo high; thus damaging the pile. In such cases, Statnamic LoadTesting is more appropriate.


17/18

1.2.1.3.3 PDA/DLT Equipment

The PDA/ DLT is operates under a Windows environment and consistof a monitoring system with a hard disk, signal conditioning, combinedsensors for strain and acceleration and cables. The PDA/DLT software

for monitoring and reporting includes many features to further facilitatesignal processing and interpretation. The PDA/DLT monitoring systemhas been designed for the harsh construction site environment.

Figure 14: PDA Monitoring System Sensor

1.2.1.3.4 Information Obtained From PDA/DLT

To assess the static performance of a foundation pile with DLT,dynamic pile resistance and the relationship between static anddynamic performance must be determined. If adequate load testing hasbeen conducted on similar piles, it is possible to obtain satisfactoryresult without a comparative static test. In this case, the followingprocedure is normally used.

During each impact loading, the following information is collected:compression and tension stress in the pile, transferred energy, drivingresistance, bending moment, maximum acceleration, pile structuralintegrity and the extent and location of any damage.


18/18

The signals and other information can be presented immediately on thescreen. A selection of the available graphs, all presented as a functionof time scaled in engineering units, include:

Measured signal

Transferred energy

Acceleration, force, velocity, and displacement at the sensorlocation

Force and velocity x impedance

Download travelling waves

Upward travelling waves

Driving resistance

Estimate of static resistance

1.2.1.3.5 Advantages of PDA/DLT System

Transducers

PDA/DLTSystem

Signal Conditioning

PDA/DLT

Software

EnvironmentPDA/DLT

Compact, reliable,water resistant,combinedstrain/accelerationtransducers,cables (on reel)and connectors

Designed and built formaximum reliabilityand durability underharsh site condition.

Programmedunder Windowsenvironment anddesigned for useby geo-technicalengineer

Mounting jig toincrease

transducer life toand for protection

Full digital signalprocessing

Easy installationof software

Junction box foreasy mountingand storage oftransducercables.

Number of files withdigitized signals onlylimited by hard diskcapacity

Higher samplerate allowinghigher qualitysignal processing

Lightweight and andsmall for easy handling

Reportingsoftwareavailable

Battery and AC

poweredAutomatic SignalConditioning

Test box to test systemfunctions

Documents

Pile Installation